MGS Tech Articles

The Reciprocating Saw: A “Fresh Look” at a Familiar Tool

Last modified on 2014-02-10 23:51:00 GMT. 10 comments. Top.

The Reciprocating Saw

A “Fresh Look” At A Familiar Tool

by Paul Bindon and Matt Stroud


Over the years we have attended and instructed at many auto extrication events around the country. When using the reciprocating saw, we have noticed varying skill levels being demonstrated by students and instructors alike. Most of the time, the saw is used at full speed, while the operator tries to hold on, as the tool throws them back and forth at 3000 strokes per minute (SPM),  until there is smoke and sparks and the blade goes dull since the teeth melted off.  A quick blade change is performed, and you are back to cutting, until the blade goes dull again, then repeat…  Often there can be a large pile of dull blades by the end of the training evolution. Many more are used by the end of the weekend. Almost all of them are missing a one inch section of teeth. We have witnessed the common trend that is referred to as, wide-open-throttle-itis!  It seems that when we (yes, we’re guilty too) get any power tool in our hands, our natural reaction is to pull the throttle until the tool has reached maximum RPM before we use it.  This “wide open” or “full throttle” power tool use has been engrained in you since you first picked up a chain saw in the fire academy.  If you train with your saw at high speed, you tend to use it at high speed in the field.  When responding to an MVA where extrication is necessary, injured patients require our best use of time.  It is a natural instinct to believe faster is always better.  Since gas engines require rotational momentum to reach the peak of their power band, it makes perfect sense to run a chainsaw or rotary saw at full throttle to keep it from stalling or binding during a cut.  Electric power tools, such as a reciprocating saw, can supply the needed torque for cutting at almost any RPM.

It seems that there has been little thought put into the proper application of the saw, the design of the blade, and the types of metal being cut during auto extrication.  A reciprocating saw is a very valuable and inexpensive tool being used around the world for many applications.  What is the best way to utilize them?

We have taken it upon ourselves to go outside the box, back to the beginning to teach ourselves how the tool operates in today’s environment with the challenges of cutting different metals. After decades of personally using these tools, the results of our extensive testing really surprised us.  In this article, we will be exploring metallurgy, tool use, blade types and design, and application, along with some little tricks we learned along the way.


Brief history of the tool commonly known as a “Recip Saw”

Milwaukee Electric Tool Corp. was the first to market a reciprocating saw named the “Sawzall” in 1951.   The reciprocating saw has a cutting action that pushes and pulls the saw blade back and forth with a counterweight that helps stabilize it.  This saw design has evolved with the introduction of features such as variable speed, adjustable shoe, quick change blades, and battery power for the electric motor. Battery power for the saw enables the operator to work just about anywhere without the need for a 120V power supply.


The anatomy of the saw and how it works

The shoe provides a bracing point for the saw and helps keep it from jumping around too much.  The shoes can be fixed or adjustable. The adjustable shoe allows the operator to adjust how deep the blade penetrates into the material being cut.


An example of a fixed shoe:

Blade Test (27)


An example of an adjustable shoe:

Blade Test (28)

As seen above, a quick change blade mechanism makes blade changes possible without tools or long delays in operation.  This makes it easy to change blades when they overheat and dull due to high speed operation.  What if you don’t have 15 blades in your pocket that may be needed to complete the cut you are doing at maximum blade speed?


 Orbiting or straight cut actions  

Some saw models have the added option of an orbital action. This action allows the blade to trace an oval pattern, lifting the teeth over the material and drawing them back during the cutting stroke for faster cutting of materials. In our testing we found no benefit in using this more expensive version of the saw.


Variable speed option

The variable speed feature enables the operator to change blade speed from 0 to 4000 SPM, with an average maximum speed of 3000 SPM.  The variable speed design that worked best in our testing was the dial type rather than trigger type, as the trigger control can add fatigue to the operator’s hand and can be difficult to use with bulky gloves.

 Two similar saws; the DeWalt saw has trigger controlled variable speed, the Milwaukee does not

 Blade Test (26)

This Milwaukee saw has a more controllable variable speed with dial type switch

Blade Test (29)


The number of teeth per inch or TPI can range from 3 to 24.  This allows the blade to be designed specifically for the type of material being cut.    The numbers on the blade indicate the number of TPI.  Lower tooth count blades are for softer materials such as wood or plastic.  Higher tooth count blades are used for harder materials such as metals.  Low tooth count blades are for rough and fast cutting.  High tooth count blades are for fine or slow cutting.  A 5-TPI blade will not cut through hard metal.  A balance must be found when selecting a blade for extrication.  It must be capable of cutting all the materials you encounter.

Blade thickness is also very important.  We found a big difference between blades commonly available at your home improvement store and the much higher quality blades used in rescue or industrial applications. Thicknesses are available from .020 inches to .068 inches. A thicker blade has better durability and heat dissipation.

Examples of blade types and brands that we tested



The example shown below is a demolition blade with 5-TPI.  It is designed to rough-cut quickly through wood with occasional nails.

5-TPI blade

 Blade Test (6)

This is an example of a metal-only blade with 24-TPI.  It has the small tooth size required for metal use, but will not quickly or effectively cut other materials.

24-TPI blade

Blade Test (20)


Here is an example of a 10-14-TPI blade designed for metal cutting.  Note the asymmetrical tooth pattern for use on a wide variety of metal thickness and hardness.

10-14-TPI blade

 Blade Test (8)

A common problem encountered when using the saw in the field is the blade falling out.  The blade’s spring loaded retaining pin in the saw failed to hold on to the blade or broke off.  What could have caused this?

All reciprocating saw blades are painted during manufacturing.  As you can see below, on some blades, the paint will accumulate in the retaining hole and prevent secure mounting in the saw.  All blades are manufactured with a standard size mounting hole for the retaining pin in the saw. Have you noticed the small tail on the mounting end of the blade?  There are many ideas about what this tail is for.  These range from “I don’t know” to “indexing the blade in the saw” to “manufacturing process”.

paint in blade hole

Here is an example of what that little tail is really for.  It is designed as a tool by all manufacturers to clean out the extra paint from the mounting pin hole in the blade.  This will allow secure engagement of the retaining pin.

Blade Test (19)

Simply twist the blade to clear out the extra paint.  Now the blade is ready for use.  (This seemed pretty obvious once we found this out.)

 Blade Test (24)

Below are some examples of blades showing different tips.  A pointed tip is designed to allow a plunge cut through materials such as drywall or sheet metal.  The blade shown on the left would not be suitable for plunge cutting. It is designed for material that has an exposed edge such as  pipe or board.

Blade Test (25)

Metallurgy 101

When cutting metal, you have to consider the hardness of different materials being cut.  This can vary from soft metals such as aluminum or brass, to hard metals such as tungsten or titanium.  If you have ever cut aluminum with a cut-off saw, you will have seen the blade gum up with molten aluminum.  Have you ever drilled into a piece of steel and watched the drill bit go up in smoke?  Why did this happen?  The answer is heat.  In both examples, metal overheated and prevented the cutting of the material.  The aluminum is softer than the cut-off saw blade.  Enough heat was generated by the saw blade to melt the aluminum and cause the blade to be clogged. The steel is at the opposite end of the spectrum.  It is much harder metal, so the heat generated caused the drill bit to melt away the cutting edge of the bit.

In each of these examples, preventing heat build-up will improve cutting performance.  There are two ways to manage heat when cutting metal; slower speed and/or use of cooling lubricant.  Industrial metal cutting machines manage heat by spraying a water-based lubricating coolant on the cutting tool. A band saw manages heat by using a slower cutting speed which enables the blade to cool as it cycles back around to cut again. The tool steel must maintain hardness in order to continue cutting the material at hand. Overheating a reciprocating saw blade causes it to lose its tempering (hardness), and the ability to cut. A reciprocating saw has a short cutting stroke (approximately 1 ½”) and is unable to cool between strokes. It will overheat quickly, the blade will lose its tempering, and the teeth will melt away. It is vital to keep the reciprocating saw blade cool.


We compared the cutting action of the same blade using different methods on a hardened steel pipe.  The first cut was performed with the saw at wide open throttle (WOT) (3000rpm) without lubricant.  The blade lasted only a few seconds before it overheated and lost its tempering. At this point the teeth melt away quickly, turning the blade into a butter knife. The blade below was used at WOT without lubricant. Note the temperature as measured with an infrared thermometer.

 Blade Test (33)

Blade Test (41)

Next, we tried the same blade type at WOT while spraying it with a dish soap and water mix.  The temperature of the blade itself was drastically reduced, but the teeth still overheated.  The blade lasted a few seconds longer, but the teeth were still melted off in a short period of time as shown below.

Blade Test (34)

Blade Test (40)

We then tried the same blade type at half speed (1500 rpm) with no cooling spray.  The blade completed our test cut.  The slower cutting speed allowed better heat dissipation away from the cutting teeth.  While the blade still reached 220 degrees and melted the paint, the heat build-up in the tooth area was not enough to damage the teeth of the blade as shown below.

Blade Test (35)

Blade Test (39)

Our last cut was also at half speed with the addition of soapy water to cool the blade.  This test cut was completed much faster than the non- lubricated blade at half speed, with the added benefit of a blade that showed almost no wear on the teeth or sides as shown below.  Note the lower temperature and tooth condition.

 Blade Test (36)

The alternating, offset tooth pattern depicted in the photo below is known as the “kerf” of the blade. This allows the blade to make a cut wider than the actual thickness of the blade, preventing binding.

Blade Test (38)

The picture below shows the difference between the cutting ability of the same blade type, using different cutting methods.

The upper blade, used at WOT, didn’t cut very far before the teeth burned up. Slowing the saw speed down and cooling the blade allowed us to complete this cut quickly with no problems.

Blade Test (46)



The reciprocating saw is a valuable tool due to its simplicity, low cost and versatility when used properly.

Saw Types and Brands

We utilized numerous types and brands of saws during our testing.  Some saws are green, some are red, some are yellow, some are battery powered, some are corded, some are $100, some are $200. Regardless, they all have a blade that moves back and forth. They all work well. The key is to find what works for you.


A slower cutting speed that does not stall the saw, combined with proper shoe use to prevent “bouncing the saw”, provides a faster cut.  Slowing down allows you to cut faster by controlling the heat produced.  Blades last longer and are able to finish the job without replacement.


We found a spray bottle filled with a 10:1 water and soap mixture to be a very simple and effective tool in controlling heat. This mixture also  lubricates  the blade cutting teeth and blade  sides to prevent binding in the cut zone. Adding a sticky soap mixture to the cutting area also cools and encapsulates the metal chip debris that could get on a patient or embedded in clothing.

Blade Selection

We tested every blade we could get our hands on and found a wide range of results.  Our favorites for extrication purposes are:

Starrett (

  • King Cut / Fire Rescue and Demolition-  Available in 6, 8,9 and 12” lengths, .063” thickness, 10-14 TPI



M. K. Morse (

  • Fire and rescue Blade -available in 6, 9 and 12” lengths .062” thickness, 10 or 14 TPI


These blades may cost more than the ones you pick up in bulk at the local home improvement store, but they will exceed your expectations of performance and durability.  You want the best tool available to perform an extrication as fast as possible.  Good blades are worth the investment.

Final Thoughts

We don’t usually do articles about tool use in the fire service., but we  thought this was important enough to spend a year researching and proving our findings.  The benefit of our testing became clear.  Slower blade speed is the biggest factor when using a reciprocating saw.  Slower is definitely faster.  A little self control and 10 minutes of practice with this valuable tool can drastically increase your proficiency in cutting during an extrication, no matter what material you encounter. Remember these three things; clean the mounting hole on the blade, control your cutting speed and lubricate the blade.

Cell Phone/Auxiliary Power Device Feedback:An Exploration of a Commonly Held Myth

Last modified on 2012-03-05 20:53:52 GMT. 7 comments. Top.

by Paul Bindon & Matt Stroud

 You have arrived at the scene of an MVA and are at the stage of powering down the vehicle to ensure all systems are off before starting your extrication procedure.  You notice that there is a cell phone plugged into the cig/power outlet in the vehicle.  Should you disconnect it?  Search for other devices in the vehicle as well?  How much time will that take at 2am in the rain?  Are you really going to accomplish anything by doing so? 

In our New Vehicle Technology for First Responder courses over the years, we have been asked numerous times about the dangers of cell phones keeping a vehicle electrical system alive after the 12 volt battery has been disconnected.  The common myth we encounter is that the Supplemental Restraint System (SRS) computer will remain energized by the cell phone battery that is connected to the vehicle through the power outlet, and may cause unwanted deployment of airbags during extrication procedures.

Let’s examine some basic facts.  When a cell phone or other battery powered device is plugged into a vehicle and the ignition is on, power flows from the vehicles electrical system, through the charger and to the device charging the battery.  What happens when you turn your vehicle off?  The cell phone or device does not power the vehicle.  If it did, your vehicle would not shut off, and the battery in the device would become discharged in a very short period of time. It is not designed to handle that large of an electrical load.  Cell phones and other battery powered devices are users of power not suppliers of power and will only allow the flow of electricity into the device battery through the charger. Not the other way around.  All electronic devices and computers use diodes (electronic one-way valves) to regulate the direction of current flow.  If power were to flow backward into a  computer it would be damaged.

Non-factory electronic devices such as sound systems or two way radios are also users of power.  No matter how they are installed, they cannot back feed power into the circuits required to keep the SRS systems functional.

All vehicle computer systems are voltage and polarity sensitive.  Just like the common laptop computer, they cannot function below a minimum voltage.  Through our research, the minimum voltage requirement for vehicle computer operation is greater than 10 volts.  Most cell phone batteries operate at 3.7 volts, with new iPhone and iPad models now reaching the 5.2 volt range.  These voltages are well below the minimum required to operate any vehicle computer including SRS.

What if a laptop computer battery (up to 14 volts) is wired directly into the vehicles electrical system (bypassing the diodes)?  The SRS computer requires multiple, separately wired power source inputs in order to operate; 12 volt battery power and at least one switched 12 volt power source from the vehicle’s ignition circuit.  Most SRS computers require more than the basic two power circuits to operate.  If a vehicle’s 12 volt power system is somehow back-fed by an outside power source, the system would have to be deliberately wired into all the required 12 volt power sources to keep the SRS computer  operational after vehicle power down (ignition off/battery disconnected).  What if that somehow happens? The airbags still cannot deploy. The SRS computer has very strict event criteria that must be met to send the command to fire an airbag. A minimum of three event criteria are required for deployment.  If even one of the event criteria is missing, the command to fire an airbag will not be sent.  Let’s talk about the three basic event criteria specifically.

1- Speed.  Can speed be measured on a vehicle not in motion?  No.  If a vehicle speed signal is not present, the command to fire will not be sent.  Side impact events use input signals of a different type.  Change in velocity (yaw rate) measured in the SRS computer is required to send the command to fire for side impact.

2- Deceleration.  Can you decelerate a vehicle that is not in motion?  No.  Sudden deceleration of the vehicle must be recognized by the SRS computer to send the command to fire.

3- Impact.  Can you make an impact on a sensor during extrication?  Yes.    It is possible to trigger a sensor during an extrication; however, if the vehicle’s SRS computer does not also see speed and deceleration, the command to fire will not be sent.

In the above pictured vehicle, we can assume that speed and deceleration (2 of the 3 deployment criteria listed above) were present by the damage to the vehicle but the airbags did not deploy. Why? The impact sensors are mounted near the headlights on the frame rail, and did not, in this case, send the required signal to the SRS computer that would have resulted in a command to fire the airbag(s) because the impact was in the center of the vehicle.  There are many other MVA scenarios where one of the three required inputs is missing.  They will also result in the SRS system not deploying an airbag.

Now you can understand why an impact signal that may be accidently triggered during an extrication procedure on a stationary vehicle will not provide all the other needed criteria for a command to fire an airbag. Neither speed nor deceleration will be present.

In addition to the required deployment criteria, SRS systems are engineered to help prevent accidental airbag deployment.  Each airbag has its own electrical circuit which consists of  two yellow wires.  These are separate power and ground wires that are run from the SRS computer to each airbag and back.  This circuit design is used to prevent accidental short circuit induced deployment.  The body of the vehicle is not used as a ground circuit like all other vehicle electrical circuits do.

So let’s talk about capacitors in the SRS computer.  A capacitor is a device for storing electricity for a short period of time.    In SRS computers, they are used as a backup power source to deploy SRS components if the 12 volt battery in the vehicle is destroyed during the MVA.  The capacitors in the SRS computer can stay energized for as little as one second and up to 10 minutes after the 12 volt battery has been disconnected and the ignition has been turned off (depending on the vehicle).  Capacitors are used as a backup 12 volt power source for system operation during a crash event if the 12 volt battery is damaged and the vehicle is still moving.  They are not used to keep the SRS system ready if the vehicle is stationary and has been powered down.

Above:  An SRS computer with internal capacitors

There is a well documented event where fire fighters deployed airbags during an extrication (Dayton, Ohio airbag incident).  Many theories have been discussed over the years as to why the airbags deployed including cell phones and capacitors.  If you review the video after reading this article, you will find that the 12 volt battery was never disconnected, and they repeatedly crushed the SRS computer during the extrication, shorting the computer.  This combination of events caused the airbags to deploy.  Cell phones and capacitors were not involved. The airbags would have not deployed if the 12 volt battery had been disconnected and/or the SRS computer had been unplugged.

Detailed SRS electronic operations and event criteria during MVA’s are very complicated topics to combine into a single article.  In this article, we have tried to explain in the most simplistic manner possible how the potential feedback of a cell phone or other battery powered device plugged into a vehicle’s power outlet is not possible.  A cell phone does contain enough battery power to fire an airbag if you wire it directly from the phone to the airbag.  This does not take into account the complex computer systems and safety mechanisms that are in a vehicle that has been manufacturered with SRS airbags.  With the information we have provided you, the myth of cell phones causing air bag deployment or keeping the SRS alive during an extrication should be busted.  Future articles by MGS Tech will discuss SRS event criteria and other SRS related topics.

Please forward any comments or questions to or visit our website to read other articles related to new vehicle technology and the fire service.

Chevrolet Volt Battery Fire; A Common Sense Response from MGS Tech

Last modified on 2012-01-09 21:21:59 GMT. 2 comments. Top.

In response to questions that have arisen from the recent publicity regarding the Chevrolet Volt battery fire at the NHTSA, we at MGS Tech have been asked to shed some light on things that are being reported, and how accurate they may or may not be.

All vehicles have the potential of fire regardless of the type of propulsion they use.  Fire fighters have been dealing with gasoline and diesel fuels as a vehicle fire hazard for over 100 years.  Electric power stored in a battery is not that different than a tank of gasoline. In both cases, large amounts of energy are stored for later use in the propulsion of the vehicle.  When a gas tank is compromised and leaking, an ignition source is all that is needed to ignite a fire.  If a high voltage battery is damaged in a collision, the potential of a direct short within the battery can cause heat build-up, potentially leading to a fire.  However, high voltage (HV) batteries are designed with safety systems that should prevent a thermal event from becoming a run-away battery fire.  In contrast to this single Chevrolet Volt battery incident, 12 volt Lead-Acid cell batteries, found in every car and truck on the road today, are a common cause of vehicle fires, and are a caustic acid spill hazard whether or not the vehicle has been damaged.

The anatomy of a HV battery can shed some light on how their design has been developed for the safety of the general public and potential first responders.  All batteries are composed of multiple cells of a lower voltage that are combined together to create a higher voltage.  This is true weather the battery is Lead-Acid, Nickel Metal Hydride (NiMH) or Lithium-Ion (Li-Ion).  The potential voltage output of a battery depends on the number of cells combined together.  A Prius NiMH battery has thirty 7.2VDC battery cells that are connected in series circuit to produce a total potential output of 210VDC.  A Chevrolet Volt Li-Ion battery has two hundred eighty eight  1.25VDC cells that are connected in a series circuit to produce a total output of 360VDC.  The Tesla Roadster EV has a 990lb main HV battery which contains thousands of tiny batteries connected together.  It should be noted that Li-Ion batteries only contain trace amounts of Lithium, and are not considered a class D fire hazard.  To put that into perspective, the Chevrolet Volt battery is reported to contain only 4 grams of Lithium in its several hundred pound battery.  Years of research and development have been devoted to making hybrid and EV batteries exceed safety standards to protect the driving public and first responders that may eventually be called on scene.  Hybrid and EV vehicles are statistically safer than their conventional counterparts due to stringent safety standards. 

A recent article forwarded to us suggested that a potential procedure is under development that would require a specialized team to respond to the damaged vehicles’ location.  This team would be trained to drill holes in the battery cells to “drain” them and make them “inert”.  However, NiMH and Li-Ion batteries do not have a liquid electrolyte.  It is actually a gel that is absorbed into the battery material.  Since the gel is not a spill hazard, it is not possible to drain them.  In our research, we at MGS Tech have taken many of these battery cells apart and verified that this is true.  In addition, due to the high cost of these batteries, destroying them in this manner when a vehicle is damaged would contribute to a much higher number of vehicles being written off as a total loss.  The concept of a major response of this type to every damaged vehicle is extreme and not necessary.

In reality, vehicles with battery damage should be inspected on a case by case basis.  Insurance adjusters and body repair estimators should be familiar with any potential issues that may arise.  It is still important to remember that all cars that have been involved in collisions have a risk of fire.  HID headlights, gasoline and diesel fuels are a much more likely cause for a car fire after an accident than a high voltage battery.  Electric and hybrid vehicles are at no increased risk.  We have confidence that the manufacturers of these excellently engineered vehicles will come up with an executable and reasonable response plan to deal with any battery issues.  Chicken Little can rest easy tonight knowing that the sky is not falling.

Matt Stroud – President

Paul Bindon – Vice President

MGS Tech



The team at MGS Tech specializes in providing  their comprehensive Hybrid/New Vehicle Technology Safety Course to First Responders nation-wide. For more information please visit the website at and go to the MEDIA tab to review previous articles.    

Supplemental Restraint Systems: Installment 1 – Airbags

Last modified on 2012-03-05 20:55:55 GMT. 1 comment. Top.

By Paul Bindon & Matt Stroud

 You have responded to an MVA and found one of the vehicles with severe frontal damage.  The front airbags have been deployed.  There is, however, something missing.  The injured driver you might expect to see is not in the vehicle requiring medical attention.  He or she is on the side of the road with no injuries, pacing back and forth talking on their cell phone trying to re-arrange their meetings for the day. 

 In the not so distant past, this scenario would not have been the case.  Advancements in Supplemental Restraint Systems (SRS) and body structure have greatly increased your chances of survival during a collision.  Just how is this accomplished?  Multiple airbags, pre-tensioner seat belts, active head rests and vehicle stability control are just a few of the specific ways modern vehicles are safer than models produced just a few years ago.  In this first of three articles, we will be taking a look at the airbag portion of the SRS system, and how it operates.

History of Airbags

Airbags have been widely available in automobiles since the early 1990’s. They are responsible for saving thousands of lives every year. Most everyone reading this article will have a vehicle equipped with a multitude of airbags. Many of us may have only a vague idea of how they actually function. This could pose a problem for first responders, who have heard that this system can be hazardous to their health, but may not completely understand why.  Many myths and fears are the result of an overall lack of understanding about the airbags and how they work. In this article, we will take a deeper look into airbags and how they function. Let’s find out what is true and what is a myth. Understanding airbags will help you act with confidence when responding to MVA’s.

Frontal airbags 

Curtain and Side-Seat Airbags 

How They Work

Simply stated, during a collision, modern vehicles will deploy various airbags in order to protect the occupants. If we take a look at the airbag itself we will find that it is made of fabric constructed from a tightly woven nylon thread that has been coated with silicone. They are extremely strong and possess incredible energy absorbing characteristics.

 If we look inside an inflated airbag right after deployment, we would find a few different gases, but there will mostly be an inert gas such as nitrogen.  The gas has to be produced very quickly in order for the system to be effective.  The gas that is used to inflate an airbag is generated in one of two ways:

#1  Pyrotechnic Inflator

Found in the drivers and front passenger locations, these airbags were the first airbags to be used on a large scale.  They contain a Sodium Azide compound that is burned to produce a rapidly expanding mixture of gases and small particulates that appear to be white powder or smoke.  This powder is white, gritty and gets everywhere when an airbag is deployed.  Talcum powder has been a nice, seemingly harmless way to characterize this substance.  This powder is, contrary to popular belief, much different than Talc.  The authors of this article have disassembled many un-deployed airbags and have never found talcum powder inside the propellant canister or on the fabric of the bag itself.  Since we are inquisitive types here at MGS Tech, we decided to find out just what this substance was.  The analysis we at MGS Tech commissioned, revealed that the white substance is not talcum powder at all.  It is mostly composed of Nitrogen gas, silica glass fibers and asbestos depleted sodium gas that you would not want on your breakfast cereal.  If you come into contact with this substance, wash your hands before wiping your eyes or eating anything.  Pyrotechnic airbags have two disadvantages:

  1. a.     White chemical smoke residue that can cause respitory and eye irritation.
  2. b.    Hot deployment gas that can cause burns to the driver and/or passenger.

Reverse view of Drivers Side Airbag 


Drivers side Sodium Azide inflator cutaway

(Note the Sodium Azide pellets and flame arresting screen material) 

Passenger side Sodium Azide inflator cutaway

(Note larger Sodium Azide discs to supply a larger amount of gas)


Burns on forearms from heated deployment gases


#2 Compressed Gas Cylinders

This type of airbag inflator has become more widely used because of its safer design.  The inert gas is stored in a small pressure vessel at up to 12,000 psi.  A small pyrotechnic device is used to puncture the pressure vessel and quickly heat the released gas that deploys the airbag.  The expanding inert gas and the super strong airbag material create a great energy absorbing device when the airbag is deployed.  The only drawback this type of system may have is the fact that un-deployed (pressurized) components remain in the vehicle as a potential hazard for fire or extrication personnel.  Clues to their placement within the vehicle can be found on interior panels as pictured below.  The existence of labeling does not in any way negate the need for “peel and peak” procedures before performing any hydraulic cutting during an  extrication, as the pressurized cylinders can be located in many different places.

Interior SRS labels 



Compressed gas cylinder for curtain shield airbag

Compressed gas cylinder for curtain shield airbag

Why They Work

It may seem obvious why airbags were created, and how it could save your life but what about the science behind it? Often the part of an impact that proves fatal has nothing to do with the vehicle at all. If we think back to physics class in high school we may (or may not) recall some of Newton’s laws. Newton’s first law states that a body in motion tends to remain in motion, unless acted upon by an outside force. Considering this law you might realize that even though our seat belt has successfully prevented us from exiting the vehicle, our internal organs have remained in motion during the collision. As they collide with the seat belt, this intensely rapid deceleration exerts unhealthy force upon them. This secondary impact often causes ruptures and internal bleeding that can sometimes be fatal. Airbags can help prevent us from receiving steering wheel or seat belt shaped bruises, and act to slow the deceleration of our bodies in an effort to ease the strain on our internal organs. In order for an airbag to perform this job effectively it needs to be fully inflated before our body reaches its’ outermost edge. For this to be possible, an airbag must deploy at a rate of 200mph or more! It deploys and becomes fully inflated in about 20 milliseconds. That is less than the time it takes for a hummingbird to beat its’ wings one time.

Example of Inertia 

 Airbags are only one part of a supplemental restraint system.  Advances in technology have allowed many active and passive safety systems to be brought to the transportation market. Having a greater understanding of SRS components can help dispel misconceptions and myths that may delay vehicle rescue actions in the field.  Future articles will explore other SRS components such as pyrotechnic seat belt pre-tensioners, active head rests, deployment sensors, deployment criteria and how they are important to first responders.

Hybrid Bus and Heavy Truck Systems

Last modified on 2012-03-05 20:56:47 GMT. 0 comments. Top.

By Paul Bindon & Matt Stroud

As we gain an understanding of hybrid systems in the vehicles around us, it is necessary to note that hybrid vehicles come in all shapes and sizes.  Hybrid systems are not just found in passenger vehicles and light duty trucks.  Large, industrial vehicles also benefit from the efficiency of hybrid operating systems.  Hybrid buses and trucks are being adopted by city and county government agencies and trucking companies, due to their ability to save fuel and reduce emissions and maintenance costs.  The financial advantages alone are causing the number of these hybrids to be constantly increasing.

Now, a logical assumption could be made that if a passenger sized vehicle has high voltage systems, the large size buses and trucks must be really high voltage (dangerous) right?  As a first responder, it is important to understand these vehicles so you will be prepared to respond without hesitation in the event of an MVA.

Why go hybrid?

Significant savings are achieved by hybrid systems in two ways; utilizing less fuel and a reduction in maintenance costs. Hybrid systems save fuel by generating electricity when they are slowing down.  This function is called regenerative braking.  The electricity generated is stored in high voltage batteries and then used to propel the vehicle the next time it accelerates.  The fuel usage of a hybrid bus or truck can be cut significantly by hybrid systems because of the way they are driven.  Continuously speeding up and then slowing down is a normal mode of operation for most of these vehicles.  For example, UPS expects to save 193,173 gallons of fuel this year with their hybrid fleet. Because of the savings potential, both Fed EX and UPS have reported that they will replace all of their delivery trucks with hybrid or electric models.

Regenerative braking also reduces wear and tear on the braking system.  The force required to generate electricity replaces friction operated brakes for much of the vehicles operation.  Since the conventional brakes are not used nearly as much with this system, fewer brake repairs are necessary.  In addition, electric drive motors are much less complicated than conventional transmissions.  They have fewer moving parts to wear out and also contribute to a reduction in maintenance costs.

Emissions reductions

The greatest amount of pollution is created during acceleration from a stop and during extended idle periods.  A 40% reduction in greenhouse gas emissions can be achieved through the use of hybrid systems.  Hybrid systems utilize the high torque of electric motors to aid in acceleration.  When the diesel engine takes over propulsion duties, it is at its most efficient range of operation.  Hybrid systems also shut down the internal combustion engine automatically when the vehicle is stationary, thus helping with “no idle” regulations compliance.  Since many cities now have “no idle” policies, hybrid systems are a very attractive way to comply with the new rules of operation.  Reduced or zero idle time regulations apply to taxi, municipal, police and emergency vehicles as well.  Ninety seconds of idle time is the norm, at which time the engine must be turned off.  How can the climate control, lights and radio remain in operation without draining the battery?  Emergency vehicles that incorporate hybrid systems to comply with new emission regulations are now undergoing field testing.  When arriving on scene, the main diesel will shut down automatically after 90 seconds if the Power Take Off (PTO) systems are not being used.  The SPS system, currently available from Spartan, automatically shuts down the main diesel and starts an auxiliary power unit that is smaller, more efficient, cleaner, and quieter to conform with these new regulations.  The next generation of fire apparatus will be a full hybrid system, utilizing electric pumps for water distribution and electric powered hydraulic systems for ladder operations.  The large diesel engine will then be used for propulsion only.

Transit and School Bus Systems

Hybrid transit bus systems resemble the passenger vehicle systems with the exception of size.  The high voltage batteries are usually NiMH (Nickel Metal Hydride) and are placed on the roof of the bus.  They therefore are away from the passenger area.  System voltages are in the 800 volt range.  The high voltage orange cables in transit buses run down the rear corner of the bus to the propulsion control system.  Note the location of the battery housing on the roof in the picture below.

Emergency shut down procedures for bus systems involve disconnecting the low voltage electrical system.  This will disconnect the high voltage system as well.  Once disconnected, the high voltage will be contained inside the battery area.  The battery disconnect is a knife type switch for low voltage batteries (24V).  This disconnect switch is mounted behind a door that is labeled “Battery Disconnect” and is easily found in either the right rear corner, or the left front corner depending on bus manufacturer.  Below is an example of the disconnect switch found on a New Flyer bus. (right rear)

The switch is usually labeled “ON” and “OFF”.  Note that this switch from a New Flyer Hybrid Bus (below) is mounted upside down.  In this case, the switch is labeled “NO” and something that might be a foreign language.

Below is an example of an Allison electric drive motor found in a New Flyer Hybrid Bus.  This type of hybrid system motor drives the wheels directly without the use of a conventional transmission, or mechanical input from the diesel engine.

Since the diesel engine does not directly drive the wheels in this system, it is linked to the generator as outlined in the diagram below from a Gillig Hybrid Bus.  This indirect link allows the diesel engine fuel system to be shut down to reduce emissions while the bus is still driving.  This is used in the city of Seattle to allow buses to operate in the underground transit tunnel without producing unsafe levels of pollution.

School bus systems differ from transit bus systems in design.  On the Enoya school bus, the 330 volt Li-ION (Lithium-Ion) batteries are located under the floor and between the frame rails.  The system shut down switch is located on the drivers control panel.  Shut off the hybrid system and the ignition switch as well when performing a power down.  Shift the transmission to neutral and set the park brakes to help stabilize the bus.

Commercial Truck Systems

Truck systems differ from buses in several ways.  The high voltage batteries are normally Lithium-ion instead of NiMH, and operate in the 400 volt range.  They are located on the frame rail where a fuel tank would normally be mounted. The high voltage portion of the hybrid truck systems is not only used for propulsion.  It can be used for several different tasks, depending on what the vehicle is designed for.  It can be used for an electric PTO only as in the case of a utility truck.  It can be used for refrigeration in a delivery truck, or as a power supply to be used during the typical 6 hour truck stop rest periods for long haul, class 8 trucks.

Shut down procedures for hybrid trucks also differ from bus systems, and involve the battery disconnect switch mounted on the battery itself.  It is a button or slap type switch that will shut down the high voltage system until the ignition key is used to restart.  The low voltage system must still be disconnected as in any conventional vehicle.

Simply depress the red button (as seen below) to shut down the vehicle’s high voltage system.

It is important to remember that stabilization is important whenever vehicles are involved in an MVA.  Buses and trucks differ from conventional vehicles in that they do not normally have a “park” position for the transmission.  The air brakes must be engaged to help stabilize the vehicle.  Look for the yellow switch you see below.

Military Truck Systems 

The military is embracing the use of hybrid and electric vehicles due to the many benefits described above plus the advantage of quiet operation.  The HEMTT (heavy expanded mobility tactical truck) is available as a hybrid, and can be configured as a mobile power generator that has the capability of producing all the electricity needed to run a field hospital.  It uses an ultra capacitor system instead of batteries to store the energy required for propulsion.  This system not only makes the HEMTT as quiet as a normal sedan, it also increases its fuel economy from 3 to 4mpg (a 20% increase).


The truck and bus hybrid systems differ from conventional vehicles mainly in size.  Stabilization of these vehicles can be more challenging due to their size, but the basic procedures are mostly the same.  Immobilize the vehicle.  Power the vehicle down.  Proceed with extrication of patients as necessary.

New Vehicle Technology Awareness for Public Safety Divers

Last modified on 2012-03-05 20:57:29 GMT. 0 comments. Top.

By Paul Bindon & Matt Stroud

We at MGS Tech have been asked the “what if” question many times by agencies; “What if a hybrid or electric vehicle is submerged? What potential extra hazards do we now have with high voltage, SRS and complex body electronic systems?”

Vehicle extrication already has its challenges without adding the element of submersion. As time has passed, vehicle technology has become more complex. The presence of hybrid and electric vehicles on our roads has become more commonplace. Hearsay and misinformation about high voltage vehicles has added another challenge to the hazardous operation of underwater rescue and vehicle recovery.

In this article, we will discuss new vehicle technology (hybrid and electric vehicles) in a submersion scenario, with the goal of a technical understanding that will prevent hesitation when responding to an incident. We dedicate this article to Public Safety Divers and Fire Rescue dive teams who risk their lives to do a job for the benefit of others.

The scenario
You are lounging in your back yard and a vehicle crashes through your fence and into the pool, causing you to spill your beverage of choice all over your speedo. You are close enough to assist the occupants immediately and are equipped by your department with rapid response dive equipment. You have to respond. What if you happen to know that the vehicle is a hybrid? Would you still just jump in? What concerns do you have regarding the technology contained in the vehicle? High voltage (HV) batteries contained in hybrid and electric vehicles (EV’s) are a concern, right? What happens to all that electricity when it is submerged? How long will the battery retain its charge underwater? What will happen to you if you enter the water and attempt to extricate the occupants immediately after it is submerged?

Note that the tail lights still function

Public safety divers encounter more new technology vehicles in the course of duties than ever before. The type of vehicle is not always apparent until after it is recovered. The training we at MGS Tech have provided to first responders has focused on treating all vehicles the same. From this point forward assume that every vehicle you respond to is a hybrid or electric vehicle so there are no surprises.

High voltage (HV) hybrid systems in vehicles today store electricity in the high voltage battery. The HV battery is used to power the propulsion systems and is not connected to the rest of the vehicle when it is turned off. To turn the vehicle on, 12V computer control is required to energize the relays within the battery that connects it to the rest of the high voltage system. If the vehicle is off, no electricity is present on the high voltage “orange wires” outside of the battery itself.

Voltage storage underwater
All batteries are part of direct current (DC) circuits. This is true whether it’s a small watch battery or a high voltage hybrid car or bus battery containing 100 to 800 volts. DC circuits have current flow that complete a loop circuit from one battery terminal to the other terminal. It follows the path of least resistance to complete the circuit back to itself. That means if the battery becomes submerged the current will not flow from the “+” terminal, out into the water, through you, back out into the water and back to the “–” terminal. It will not, for the same reason, cause the body of the vehicle to become electrically charged. The battery will short internally. SRS deployment by the high voltage system underwater is also not possible for the same reason. The current would have to travel from the high voltage battery terminal, through the water, into one SRS airbag wire, through the airbag, back out the other SRS wire, through the water and back to the battery. The current will instead take the shortest path possible from the “+” terminal within the battery to the “–” terminal within the battery. Airbags require a voltage from the SRS computer to deploy. They will not deploy if electricity is applied to the body of the vehicle as a result of a crash and/or damage. Their wires are not integrated into the vehicle body circuit (ground). Each airbag has its own “+” and “–” wire that are not close enough to the high voltage battery to become energized through the water if the vehicle is submerged.

High voltage DC circuits in hybrid vehicles are also self-contained, and insulated from the rest of the vehicle. They also have their own “+” and “–” wires that do not interface with the body of the vehicle as part of the circuit (ground). All production vehicles are also mandated to have computer monitored safety systems that will isolate the voltage to the battery if damage to the vehicle somehow causes a high voltage system short to the body. Using the body of the vehicle as part of the circuit is, however commonly done with 12V vehicle circuits to simplify the wiring.

For more information, please review the “Basic Electrical Theory” article on our website at

When the battery is submerged
The amount of time voltage is present inside a high voltage battery when it is submerged depends greatly upon the water quality. Water will conduct electricity better when it has contaminates in it. Clear fresh water has a very high resistance and will not conduct electricity as well as salt water or water containing a high mineral content. The discharge rate of the battery is also dependant on the voltage. You may have encountered a submerged vehicle that still had the headlights on. The fact is a 12 volt vehicle battery will retain its charge underwater much longer than a high voltage hybrid battery underwater. This is because higher voltage is better able to push through the resistance of the water and complete the circuit to the opposite terminal, thus discharging more quickly than a lower voltage battery.

So, what actually happens when a high voltage battery discharges underwater? Hybrid and electric vehicles use Nickel Metal Hydride or Lithium Ion high voltage batteries. When either of these batteries is submerged, the flow of electricity through water from terminal to terminal inside the battery will actually split the H2O water molecule as it discharges. This will produce Hydrogen and Oxygen in a gas form. This process is commonly known as electrolysis. The amount of gas accumulation depends on the original battery voltage, water quality, how well the vehicle is sealed, and the amount of time underwater. To prevent these gases from becoming a fire or explosion hazard if they accumulate, simply ventilate the vehicle appropriately when it is removed from the water by breaking the glass or opening the door.

Example of a Lithium Ion battery from the Chevrolet Volt

To see firsthand what happens when a high voltage NiMH battery is submerged in salt water, and the amount of electricity actually found in the water during submersion, click on the link to watch our “HV Battery Submersion Test” video.

How electronics react to water
It has been observed that vehicles underwater have functioning headlights and power windows. Visible clues that the 12 volt system is operational may lead us to believe that all systems in the vehicle are still working; however, vehicle computers are not designed to operate in a submerged environment. They will cease to function if they become wet. An example you may have had firsthand experience with is a cell phone falling in the toilet. You might have a small chance to save the phone if you can dry it out properly without turning it on. If you drop that same phone in salt water, it is history! Like the cell phone, when automotive computers get wet, they also cease to function. Early designs of supplemental restraint system (SRS) computers were located in the center console area but real world use by the general public quickly highlighted the need to protect them from spills. Rather than developing submergible computers, auto manufacturers simply provided a shield for the top of the SRS computer to protect it from that “super-size” soda spill. Newer vehicles now locate the SRS computer in a more protected location. They are generally found toward the firewall in the center console area. Similarly, the 12V controlled HV battery computer ceases to function when submerged. The HV system will then cease to function, and voltage will be contained within the battery. There will be no voltage on the orange wires.

The hazards posed by modern hybrid and EV vehicles are not much different than conventional vehicles. While the safety of the diver must still be paramount, the technology contained in the vehicle should not prevent you from performing your duties. You can safely approach these vehicles without fear of electrocution. However, even though newer technology vehicles often contain fewer fluids as compared to conventional vehicles, fluid loss from damaged fuel systems and lubricating oil is still a concern. As with any submersion situation, hazards, including water quality, temperature, entanglement and Hazmat are still present and should be given proper consideration. Adequate protection for the diver must be used in every case possible.

Since it is not always apparent that a vehicle is a hybrid or EV when it is involved in an accident or submersion, it makes sense to treat every vehicle as if it is equipped with a high voltage system, multiple airbags in the SRS system and HID headlights.

For more information regarding HID headlights, please review “HID Lighting: A Bright Idea?” article on our website at

Hybrid Under-ride Solution

Last modified on 2012-03-05 20:58:18 GMT. 1 comment. Top.

By Paul Bindon & Matt Stroud 

The purpose of our previous article was to encourage creative thought about a situation that would normally have a straightforward approach.   As the MVA was evaluated, however, it became more apparent that the technology contained in the vehicle could make reaching the patients in the vehicle more complicated. It was deliberately designed as a tough “what if” scenario, with very specific circumstances involving a hybrid vehicle. There are several ways to approach the situation that we will discuss in this solution.   Many thanks to the very knowledgeable individuals who responded with their intelligent and practical solutions to the Honda Civic Hybrid under-ride MVA scenario article.

Examining the solutions

Many of the submitted solutions assumed that it was possible to disconnect the 12V battery.  While this should be an essential part of vehicle immobilization, the 12V battery is located in the front of the Honda Civic Hybrid and the scenario stated that there was no access to this part of the vehicle.  This means that the SRS, hybrid systems and possibly HID headlights could still be powered up. (For more information regarding HID headlights, follow this link:


Under-ride MVA’s often do not deploy the SRS airbags and you cannot count on an electronic system to automatically disconnect the fuel pump, high voltage and SRS systems.  It should also be noted that not all hybrid vehicles are equipped with an auto disconnect for the high voltage system that is linked with SRS deployment.  In our description of the MVA, it was stated that the vehicle was on and running.  Since the engine is still running, you should expect that an automatic safety disconnect of the vehicle systems has not happened. Ideally, if the driver is able, turning off the ignition would prevent some of these systems from being on and active, but would not totally eliminate them as a potential hazard.

Lifting the trailer using air bags and cribbing is an excellent approach if you have the tools available to do so in a timely manner.  Some departments do not have the amount of cribbing necessary or air bags needed for this type of vehicle removal.  If your department does, you have vehicle removal as an option, but only if response time and patient condition allow you the time necessary to perform the extraction.  If you do not, this would mean that stabilizing the trailer, vehicle, and then proceeding without removing the Honda would be the best approach.

Here is an alternate approach to the described scenario of the Honda Civic under-ride MVA.

Step One

Stabilize the Honda by using ratchet straps attached to the wheels and routed over the rear of the vehicle, to prevent suspension movement when parts are removed from the vehicle.  Stabilize the trailer with available material; cribbing, struts or even high-lift jacks can be used.  Your choice will depend on how level the terrain is and what equipment you have available.

Step Two

Perform a tunnel operation through the trunk by first removing the trunk lid and interior trunk trim. You will now have a view of the back of the high voltage (HV) battery housing as pictured below in Photo #1.  Now, using cutters or a recip saw, cut away the rear package tray as seen from the front, in Photo #2. You will now have a view of the back of the HV battery but still won’t have access to wires, switches and mounting bolts which are located on the HV battery front, facing the passengers.

Photo #1

Photo #2


Step Three

Still from the back, continuing with the saw, cut down on the outside edges of the battery box as pictured in Photo #2, allowing the HV battery to fall towards you into the trunk. You now have a view of the HV battery with the 12V wires, orange wires, switches and bottom mounting bolts visible. Both Photo #2 and Photo #3 show a Honda Civic HV battery viewed from the front, with the cover plate removed.  In Photo #3 note the location of the actual HV battery on the drivers’ side of the battery box.  The passenger side of the box is used to store the DC/DC converter and HV battery control systems.  Note the location of the 12V system wiring on the drivers and passengers side bottom corners.  The high voltage “orange wires” exit the battery box on the passenger side lower corner.

Photo #3


Step Four

As shown in Photo #4, the service disconnect switch is mounted on the front of the battery, and is now accessible.  Remove the small bolt on the cover for the service disconnect and flip the switch from “on” to “off”.  This will eliminate the connection of the high voltage battery to the rest of the vehicle, but will not give you a visual indication that anything has happened.

 Photo #4

The high voltage is now contained within the battery itself.  Cutting the 12V wire harness on the drivers and passenger side will also eliminate any possible computer system connection to the rest of the vehicle, but will also give no visual indication of effectiveness.  Since the “orange wires” will no longer contain voltage, they can now be cut to remove the high voltage battery from the vehicle.  Continue with extrication as you would with a non-hybrid Honda Civic.

Step Five

Remove the rear seat back. Package the two children from the rear seat area and remove on backboards if needed. Depending on vehicle roof condition, a hydraulic ram may be used to maximize the space necessary to continue.  Use power or manual seat adjustments if possible to help access the patients in the front.  If no easy adjustment of the seat is possible, proceed with caution during seat back removal as the vehicle may be equipped with side SRS airbags and seatbelt pre-tensioners that contain pressurized gas cylinders and pyrotechnic charges.  Cut the seat cover material and inspect for hazards before cutting the seat frame material.  Headrest DVD players, power seat motors and seat heaters have power sources that should be eliminated before cutting seat SRS wire harnesses.  These systems would not be a concern on a vehicle that was first powered down by shutting off the vehicle and removing the 12V battery negative cable.  Lower seat removal may be necessary if there are entrapment issues with the patient’s lower extremities. Finally, remove the front seat passengers.


Can a tunnel method be used on any Hybrid vehicle with a vertically mounted HV battery?

Honda Civic Hybrid 03-05
Honda Civic Hybrid 06-current
Honda Accord Hybrid 05-07
Ford Fusion Hybrid
Mercury Milan Hybrid
Lincoln Mark Z Hybrid

Yes it can! Once you understand how the technology works, you can easily and safely use the tunnel method to manage this “what if” scenario.

Yes, there are multiple methods that would allow you to safely remove the patients from this vehicle but depending on your unique circumstances; it’s nice to have another option to choose from.

Scenario MVA

Last modified on 2012-03-05 20:59:15 GMT. 0 comments. Top.

Scenario MVA

By Paul Bindon & Matt Stroud

In previous articles, we have focused on the types of technology found in vehicles around us.  We can now apply what we know in a real life scenario, see what problems may arise and illustrate possible solutions that may be used.

Keeping in mind that hybrid vehicles have 4 tires and a steering wheel just like all the other vehicles on the road today, the major difference is its propulsion system.  Take a conventional vehicle, add a traction motor and high voltage battery, and you basically have a hybrid.  This is over simplified to be sure, but makes the point that extrication procedures will differ little between hybrid and conventional vehicles in most cases.  Consider the diagram below.  Note the position of the high voltage battery, orange high voltage wires and inverter/traction motor.    Can you remove the roof of this vehicle for patient access without encountering the high voltage system?

Yes you can.  The high voltage components are not located near the pillars supporting the vehicle roof.  We can take this a step further and also see that extrication procedures involving door removal, dash displacement and B pillar removal are also not affected by the high voltage components.  Since most MVA’s involve vehicle damage that allows patient access with these methods, procedures will not differ in these cases just because the vehicle is a hybrid.  Most hybrid vehicle manufacturers place the high voltage battery under the rear seat (SUV) or low in the trunk/cargo area.  Some sedans, such as the Honda Civic/Accord Hybrid and the Ford Fusion/Mercury Milan/ Lincoln Mark Z Hybrid, have high voltage components such as the battery behind the seat in a vertical position.  This may save cargo space in the trunk by placing these parts up against the back of the passenger seats, but it can also limit access when performing a tunneling operation through the trunk of the vehicle.

All hybrid vehicles have a high voltage battery disconnect (also known as the “orange plug”) of some kind on the high voltage battery.  The location of this disconnect will vary by vehicle type.  Some are easily accessible like the Ford Escape Hybrid or Toyota Prius which are located in the rear of the vehicle.  Others are not as easily found.  There are several hybrid models including the Honda Civic Hybrid that place the high voltage battery disconnect on the front side of the battery, located behind the rear passenger seat back.  To access the high voltage battery disconnect on these models, the rear seats must be removed.  The original purpose of these disconnects was to isolate the high voltage electricity within the battery assembly for maintenance purposes.  Little thought seems to have been given to first responder access to these disconnects.

Removing the high voltage disconnect will disable the hybrid system (propulsion only).  You may have thought that pulling the orange plug was a complete power down in the past, but this is only part of the necessary procedure. All systems in the vehicle are controlled by the 12V battery including SRS and the HID lighting systems, which will require further action before the vehicle is properly powered down.

SRS systems are controlled by computers that run on 12V.  Capacitors in the SRS computer will keep the system operational for a period of time after the 12V battery has been disconnected.  These capacitors are designed to allow the system to remain operational if the vehicle’s battery is damaged in a collision, and the vehicle has not yet come to a stop.

The wiring for the SRS system is not integrated into the circuits for the rest of the vehicle.  Airbags have their own “+” and “–“ wires that do not use the body of the vehicle as part of the circuit (ground).  The electrical power needed to deploy the airbag is supplied by the SRS computer.  This computer is supplied with a constant 12V power source from the battery and a switched power source from the ignition circuit.  Each of these two power sources must be available for the computer to be operational and be able to deploy an airbag.  Auxiliary power sources, such as cell phones, that are connected to the vehicle are therefore unable to power the SRS system and accidently deploy airbags.

HID System Importance

High Intensity Discharge (HID) lighting systems also run on a 12V circuit.  These systems use a step up transformer to create an electrical arc within the quartz tube of the headlamp bulb.  The operating voltage of this system is approximately 25,000V.  This arc heats up the gas within the tube to create a very bright light source.  This high voltage/low amperage system does not create a lethal amount of voltage, however the arc is hazardous as an ignition source, and as an electrical shock as well.  Vehicles that are damaged in a frontal collision have the potential to arc if you come into close contact with that part of the vehicle.

Now, let’s build a scenario and see how it unfolds.

A Honda Civic Hybrid is travelling on the freeway with 2 adults and 2 kids inside.  The driver fails to notice stopped traffic and collides with the rear of a big rig truck.  The vehicle is buried under the rear of the trailer up to the C pillar.  There is no roof or side door access to the patients inside.  They are in need of medical attention, and the heavy wrecker is already responding to another incident and is therefore unavailable.

After your 360 degree evaluation from a safe distance, you have determined that the Honda is on and running. Neither vehicle is on fire and you have found the truck has a load of fluffy soft down pillows. No flammable fluid leaks were found.  You have the equipment available for proper vehicle stabilization.

After stabilization of the vehicles, the best approach in this situation to the extrication is to tunnel through the trunk to reach the patients and remove them from the vehicle.  After removing the trunk lid and trunk interior trim, you see component #3 in the figure below; the high voltage battery.

Honda Civic Hybrid Trunk View

The battery pack covers the width of the trunk opening between the wheel wells.  There is not enough room to go over, under or around it.  Common sense tells you that you must somehow remove the high voltage battery.  Conventional training has taught us to avoid touching, cutting or moving the orange high voltage wires.  Since this is apparently not possible in this situation, a decision must then be made as to how to deal with the high voltage components of this vehicle.  Are you going to follow your previous training and not be able to reach the patients?  What other options do you have?  Using the knowledge you have, a solution must be found for this situation.

This scenario is set up with enough information to prove a point.  The real life aspect of this scenario coupled with the knowledge previously provided should enable you to realize that previous tactics provided by vehicle manufacturers are not an option.  The legal ramifications and perfect scenario perspectives of “official” guidelines and recommendations do not apply to the real-life situations often encountered by fire/rescue personnel.

The point of this exercise is to show that there is a solution to the problem.  The time for questions is over. What would you do?

In our next article, we will explore possible solutions to the scenario, including those submitted to the link below.

Send your solution and your source of information to

Mid Voltage/Low Voltage Automotive Systems

Last modified on 2012-03-05 20:59:58 GMT. 0 comments. Top.

By Paul Bindon & Matt Stroud

Automotive electrical systems have been evolving quickly, as new technology is integrated in our transportation systems. We have previously discussed high voltage electrical systems in hybrid vehicles. It is also important to understand other electrical systems and how they may be important during extrication. We will be discussing mid voltage “hybrids”, as well as some key 12 Volt systems found in vehicles today.
Mid voltage hybrid vehicles were relatively inexpensive alternatives as compared to the hybrid vehicles from Toyota and Honda. This cost savings was accomplished by using a relatively simple technology that allowed the gasoline engine to shut down when the vehicle was slowing down, and when it was sitting at a stop light. A large electric motor/generator, located between the engine and transmission, was used to restart the engine very quickly when the throttle pedal was applied. When these vehicles are braking or slowing down, the motor/generator is used to recharge the mid voltage battery pack. To be able to power a motor large enough to start the engine quickly, a larger battery capacity was required than a standard 12V system could supply. Mid voltage “hybrids” were equipped with 36-42V battery packs. Early models had three 12V lead-acid batteries that were connected in series to form the required battery voltage. Later models were equipped with newer technology NiMH units. The mid voltage battery was used exclusively for the “hybrid” system, and are not involved in the operation of other vehicle systems such as SRS (airbags).
Mid voltage “hybrid” vehicles use an industry standard color for their wiring. All wires found in mid voltage “hybrids” that contain the 36-42V electricity are colored BLUE. They do not contain a lethal amount of voltage. The blue wire coloring indicates an increased arc hazard. Each mid voltage “hybrid” was also equipped with a conventional 12V battery which powers all other electrical systems in the vehicle.
Below is an example of the mid voltage battery pack and blue wiring which indicates a 36-42 volt system. This battery, from a 2009 Saturn Aura, is located in the trunk of the vehicle.

This is an example of the 12V battery location from the same vehicle. Note the blue wiring in the engine area.

Simple diagrams for battery location can be found under the hood of some mid voltage “hybrids” such as the example below:

The other possible location for the mid voltage battery us under the rear seat (truck), or cargo floor (SUV).
An overview of system components is shown below for the Saturn Aura sedan:

Mid voltage “hybrids” were released from several automotive manufacturers as an attempt to bring to market their own version of eco-friendly vehicles at a time when the public was becoming increasingly aware of their impact on the environment. While they were marketed as “hybrids”, they do not have some of the key characteristics of a true hybrid.
-They Do Not contain a high voltage battery.
-They Do Not contain orange high voltage wires
-They Do Not use a high voltage motor that drives or assists in driving the wheels.

Because of the above listed differences, they are not considered to be true hybrid vehicles by most automotive experts.
The first mid voltage “hybrid” vehicles were the 2004 model year GM Sierra and Chevrolet Silverado full size pickup trucks. Marketed as contractor friendly trucks, they were equipped with an 110V AC power outlet in the truck bed. Advertising featured the truck being used as a power base by a contractor to build a home in a remote location. Unfortunately, the available power from the bed power outlet was limited to the point where high load items such as power saws were unable to be used. Although modest gains in fuel economy and emissions reductions were realized with this technology, production of these trucks was halted after the 2006 model year.

Chevrolet Silverado Mild Hybrid

Later mid voltage “hybrids” offered by GM and its related companies were the 2007 Chevrolet Malibu, Saturn Aura and the Saturn Vue compact sport utility vehicle. These vehicles used the same mid voltage systems to enhance fuel economy and reduce emissions. A cost premium over the conventionally equipped vehicles made them less desirable to the general public and they were discontinued after the 2009 model year.


Cutaway view of a mid voltage hybrid vehicle

As with other hybrid vehicles it is very important to remember that the vehicle is a silent running hazard. Just because the engine is not running, it has the potential to move without warning. It would be embarrassing and potentially dangerous to have to relocate the scene for patient extrication if the vehicle suddenly drives away with one of your team members stabilizing the patient in the vehicle. Normal procedures should be followed for vehicle stabilization before any entry into the vehicle is made.
All computers in vehicles today are run off of the 12 volt system. It is important to remember that disconnecting the 12V battery will prevent the SRS system from operating. This should be a primary goal during vehicle stabilization prior to any extrication procedures being performed.
Mid voltage “hybrid” vehicles have been discontinued from production for a variety of reasons. They are, however, still to be found on the road today in a large enough number to justify being aware of their technology, and how to handle it. Increased arc hazard from the mid voltage system and the ability to move suddenly when the engine was stopped are the main points to remember.

Vehicle Electrical Circuits

Last modified on 2012-03-05 21:01:31 GMT. 0 comments. Top.

By Paul Bindon & Matt Stroud

Modern Hybrid vehicles contain a wide array of technologies.  Trying to understand the hazards associated with these systems is essential for first responders.  What are the major components to consider during your approach and extrication, and where are they located?  This article will be a review of some of the systems you may encounter when responding to a MVA involving a Hybrid vehicle. 

Vehicles are manufactured following strict standards for safety in design.  High voltage components are required to be insulated from the body of the vehicle to a very high degree.  There is however, no absolute guarantee that there is not a hazard to you, as a first responder, when the vehicle has been altered in an MVA.

High Voltage Battery Pack-

All batteries are part of a direct current or DC circuit.  Consisting of many cells with lower voltages, they are connected in series to produce voltages ranging from 100V in Honda systems to 800V on Hybrid commuter buses.  Battery cells contain a gel type electrolyte suspended between metal plates which do not pose a spill hazard.  Most current models are equipped with NiMH (nickel-metal hydride) batteries, the same technology your power tools at home use.  You may have noticed the battery for your drill will run normally and then suddenly die.  Vehicle batteries obviously cannot operate the same way because stranded motorists are not good for sales.  To prevent this, the state of charge of a Hybrid vehicle battery is maintained by a computer that does not allow the battery to either completely charge or completely discharge.  The vehicle uses braking energy or the engine to maintain battery charge levels, allowing prolonged battery life.  One common misconception is that the high voltage battery will have to be replaced after a period of time.  In reality, the batteries are designed to last the life of the vehicle.  Hybrids in commercial use, such as taxi cabs, have been driving for 200,000 to 300,000 miles on the original battery without failure.

Lithium Ion batteries are emerging as the next generation of battery technology.  They allow much longer use before becoming discharged, thereby increasing the fuel economy of Hybrid vehicles.  While the name of the battery uses the word lithium, they actually do not contain lithium metal.  As with all rechargeable NiMH or lithium type batteries, they do not require a class D extinguishing agent in the event of fire.  Large amounts of water would be an acceptable extinguishing agent for any of the Hybrid battery types produced to date.

Examples of a Prius High Voltage Battery

(Note location of battery under floor, behind rear seat)

Prius Battery with Individual Cells Exposed


Inverter/ Converter-

The inverter/converter is the computer control or brain of the Hybrid system. Located in the engine compartment, on top of or near the traction motor, it converts DC battery voltage to higher voltages for use by the traction motor.  Up to 650V can be found inside the inverter/converter. It is also the charging system for the high voltage and 12V batteries.  Because the inverter/converter is located in the engine compartment, cutting or removing during extrication is not necessary.

Example of Toyota Inverter/Converter

Traction Motor-

All true Hybrids contain a traction motor(s) that drive or assist in driving the wheels.  These motors are also used as generators to recapture braking energy and charge the high voltage battery. Traction motors can contain up to 650V AC when in operation.  They are located between the engine and transmission as an assist motor (Honda, Mercedes) or within what would normally be the transmission (Toyota, Lexus and other manufacturers).

 Example of a Lexus RX400h Traction Motor

Air Conditioning Compressor

Since the Hybrid vehicle’s engine does not run at all times, a conventional air conditioning compressor utilizing a drive belt and pulleys cannot be used.  The electric air conditioning compressor is used when air conditioning is needed.  System operation does not affect power available for driving, since it is not run by the gasoline engine.  Electric power drawn from the high voltage battery is used to run the 300 volt motor.


Electric Air Conditioning Compressor


High Voltage Orange Wires-

All wiring used in automotive applications that may contain over 60 volts DC or 30 volts AC is colored orange.  It could be 60V or 800V, the wiring color is the same.  This simply means that it may contain enough voltage to be a lethal hazard to you as a first responder.  These wires run from the high voltage battery, under the vehicle in protective sheathing, forward to the inverter/converter in the engine compartment.  They also run from the inverter/converter to the traction motor and to the air conditioning compressor.  Since they do not run inside the passenger area, they should not be encountered during most extrication procedures.   

Examples of DC Orange Wires from Battery to Inverter

Note AC Orange Wires on Top of Traction Motor


Mid Voltage Systems-

Electric power steering systems became necessary since, in a Hybrid vehicle, the gasoline engine is not always running.  Conventional power steering systems, which are run by belts and pressurized fluids, were no longer an option.  Electronic power steering systems run on 40V to 50V DC (below 60V), therefore they do not require orange wiring. A dull yellow wiring color for this system signifies less than lethal voltages.

Example of a Lexus Electronic Power Steering Rack

Mild Hybrids or mid voltage Hybrids do not contain a traction motor that drives or assists in driving the wheels.  Mid voltage battery packs (36V-42V) are only used to provide enough power to start and stop the engine when coasting, or for a brief period of time at a stop light.  This strategy yields a mild increase in fuel economy.  They were however marketed as Hybrids and have led to some confusion regarding the difference in wire color.  Blue wiring has been used with these systems to signify mid voltages. Although they do not contain enough voltage to be a lethal hazard, increased arc hazards should be noted when dealing with these vehicles.

Low Voltage Systems-

It is important to remember that all Hybrids have a conventional 12V battery that powers all accessory systems such as power windows, radio, SRS etc. The 12V battery is required to power the computer, which closes the relays connecting the high voltage battery to the rest of the system.  If the 12V battery is taken off line (disconnected by cutting the negative battery cable) the high voltage system cannot restart.   Remembering that the 12V battery is the key to disabling vehicle systems will aid in quickly stabilizing vehicles for patient extrication procedures.

Prius 12V Battery – Located in RH Rear Corner of Vehicle

(Note red plastic cover over the “+” battery terminal)

Conventional vehicle braking systems rely on engine vacuum or hydraulic pressure to provide power assistance.  This system was also redesigned for Hybrid vehicles.  Electric/hydraulic brake systems are now used, allowing operation when the engine stops running.  Computer controls regulate the amount of power generated for the battery based on how much braking is required. A separate system is used to simulate the conventional feel of power brakes we have become used to.  These systems contain a 12V backup power supply in case of failure.

This review of the major electrical components of modern vehicles has been intended to help first responders familiarize themselves with the potential hazards involved in patient extrication.  Knowing what these components are, what they do and where they are located can take some of the mystery out of modern vehicle technology.

Basic Electrical Theory

Last modified on 2012-03-05 21:00:46 GMT. 2 comments. Top.

By Paul Bindon & Matt Stroud

 Electronic devices are run by smoke.  When they become damaged or fail, the smoke escapes and they no longer work.

This explanation of how electricity works may seem comical, but it highlights the mystery surrounding electricity as something we cannot see.  The results of electricity at work are obvious to us; the lights turn on, the motor turns and the stereo plays music.  In contrast, the flow of electricity through wiring becomes somehow mysterious or even frightening when high voltages are considered.

The use of high voltage in transportation has caused some uneasy or wary approaches to vehicles involved in collisions.  When considering hybrid vehicles, high voltage orange wires come to mind.  “Don’t touch the orange wires” has been the most common message that has been relayed to first responders during hybrid training.  Why should you not touch the orange wires?  When asked this question, most first responders I have talked to reply with either “because they are high voltage”, or “because they will shock or kill you”.  This basic message of caution is the reason many responders may hesitate or delay the approach to patients when hybrid vehicles are involved in an MVA.  In this article we will cover a basic understanding of electrical theory as it applies to transportation use, with the goal of dispelling some of the mystery of electricity.

DC circuits

All batteries operate DC or direct current circuits.  This is true of small watch batteries all the way up to 800V hybrid bus batteries.  Current in a 12 Volt DC circuit flows from the positive (+) terminal of the battery through the weakest link (fuse), through a load device (bulb), a control circuit (switch) to the chassis or frame then finally the negative (-) terminal of the battery.  This is considered conventional electrical theory.  It is important to note that the vehicles body or frame is used as part of the circuit.  For low voltage applications this is perfectly safe, and simplifies the wiring.

A simple example of a DC circuit is the 12V circuit shown below.

1       The power source in this case is the conventional lead/acid 12 volt battery.

2       The circuit has a weak link (fuse) that protects the rest of the circuit in the event of an overload.

3       The load device (bulb, radio etc.)  This actually puts the power to work, and is the visible indication of what the electricity actually does.

4       On/off switch or some type of circuit control.

5       Body or frame of the vehicle (ground).  This is the return path for the electricity back to the power source.

AC circuits

Wires in an AC or alternating current circuit contain positive and negative voltage on the same wire.  There are typically 3 wires associated in a household 110V circuit.  They are black (hot), white (common) and bare (ground).  AC circuits use terra firma or ground as part of the circuit.  Anyone who has become part of an 110V household circuit can tell you this is true.

Hybrid vehicles do not use terra firma “ground” for their AC circuits like household electrical circuits.  Since the tires insulate the vehicle from the ground, they would require some type of connection to the “ground” in order to operate the same way.  There obviously is no wire running behind the vehicle or hanging down touching the ground as it is being driven along.  The vehicle AC circuit is therefore self-contained and does not use the chassis or frame of the vehicle as part of the circuit.

Household grounding wire

Voltage vs. Amperage


A stun gun is an example of a “high voltage” device.  They operate with between 100,000 to 1.5 million volts.  The reason they are not lethal is that they do not provide enough amperage.  High voltage certainly, but low amperage output (1 to 5milliamps).  Compare this example to a fire apparatus pushing water through a garden hose.  High pressure (600psi) running low GPM because of the restriction of the small hose.

A 12V car battery can produce 500 to 1000 amps.  This example is not lethal because the voltage is too low to overcome the naturally high resistance of our bodies.  If you connect the terminals of a car battery with a piece of steel however, the low resistance across the terminals will result in maximum current flow (lots of sparks).   Compare this to a hydrant feeding a 5 inch line; low pressure providing very high GPM.

Have you ever heard the expression “It’s the amps that kill you”?  This statement is an over-simplification of the hazards associated with electricity.  There has to be a threshold where the voltage and amperage become hazardous.  The SAE industry standard wire color for hazardous voltage is orange.  This means that the voltage contained on an orange wire is over 60V and over 1 amp.  It could be 60V or 800V, the wire color is the same and should be considered potentially lethal.

High voltage circuits in vehicles do not use the body or frame as part of the circuit.  The DC high voltage wiring (orange) include the Positive and Negative cables.  This is done to insulate the body of the vehicle from the high voltage circuit.

DC Orange wires from high voltage battery to inverter

The AC high voltage wiring includes all 3 parts of the circuit.  This is done to insulate the body of the vehicle from the high voltage circuits.

AC Orange wires from inverter to traction motor

Safety systems are included to prevent the body or frame from becoming part of the circuit in the event of possible damage.  Each high voltage wire is wrapped in a layer that is monitored by the vehicles computer.  If the wire becomes damaged, the system is designed to cut the connection from the high voltage battery and isolate the high voltage inside the battery.  Other systems are designed to do the same thing in the event of SRS or airbag deployment.  It is important to know that the high voltage system is controlled by the 12V system in the vehicle.

Understanding the basics of how electricity works can help dispel some of the myths surrounding high voltage in the transportation industry.  Knowing that electricity is more than what we can see will help prevent hesitation when dealing with the emerging technologies of today.

HID Lighting: A Bright Idea?

Last modified on 2016-06-06 22:29:36 GMT. 0 comments. Top.

HID Lighting: A Bright Idea?

by Paul Bindon & Matt Stroud

As you are driving one evening, you round a corner and all of a sudden you are blinded by bluish-white beams, piercing the dark. Face to face with a UFO? 747 landing lights? Entrance to the pearly gates?

You have just witnessed HID lighting at its finest.

High intensity discharge lighting or HID seems to be installed in all sorts of vehicles. It used to be only in high end BMW or Lexus models, now they are in that multi-colored 1985 Honda Civic, truck accessory lighting and even in motorcycles. You might even have them installed on your engines and ladders as floods.

So what are they and how do they work?

The use of HID lighting began in the early 90’s in higher end European models. The US and Japanese manufactures adopted the HID system in the mid 90’s. Lincoln, Acura and Lexus were just a few of the companies using this technology. Since then, almost all manufacturers have offered models with the HID headlight system as standard or optional equipment.

So, how do the HID systems work? To better understand this new technology you must first have a good idea of how conventional headlight systems function. Conventional systems use a bulb containing a filament that produces light when voltage is applied; the same as a standard light bulb you use in your home, these bulbs have a short life span and are fragile. The light produced has a yellowish hue and is rated in watts. Most conventional headlight systems are D.O.T. rated at 55 watts and the voltage they use to produce their light is 12 volts. HID headlight systems work very differently. Rather than using a filament, the HID bulb is comprised of a quartz capsule that contains xenon gas, mercury (2004 & earlier HID bulbs) and metal halide salts with tungsten metal electrodes at each end. An arc is formed in the capsule by a high voltage current that is produced by the HID control unit in each headlight assembly. This control unit draws 12 volts from the vehicle and steps it up to as much as 25,000 volts. Think of it as a controlled lightening strike in a small bottle. The light emitted from this process is rated about 4,000 Kelvin (K). A Kelvin rating is a method used to describe theoretical temperature of color. To put this into a perspective more understandable to us all, a conventional headlight bulb is rated about 2,800 K which produces a yellow or amber colored light. A halogen headlight bulb is rated about 3,200 K. These bulbs produce a much whiter color of light. HID bulbs produce a bluish-white color of light, rated about 5,000 K, which is closest to natural sunlight at midday. Emitting this color of light from the front of a vehicle at night allows the operator the ability to see and react faster and more accurately to obstacles in the road.

So, that’s great, now we all know how the HID system works. That’s fine and dandy but that’s normal operation in a vehicle driving down the road. What happens when the vehicle crashes? As emergency first responders, you know that nearly 99% of vehicles in accidents sustain some sort of damage to the front end. The headlights were probably broken.  What about that nice bluish-white light emitting, 25,000 volt headlight system? Well, here is where it gets interesting.  The HID system does not care that the car has been damaged; the system is still trying to function. The controlled lightening strike we mentioned still needs a place to go. This can create a serious hazard for first responders who could come in contact with this extremely high voltage. To put this in context, if you have ever been shocked by a spark plug wire on a lawnmower or vehicle, you probably remember how that felt. (!%@*!@) The HID system voltage is a constant 25,000 volts and works more like a taser or stun gun. It has a higher refresh rate and therefore a much higher shock danger and can also pose a greater risk of a fire being ignited.

When responding to a MVA, it is common to need access to the engine compartment for fire suppression or to disable the 12 volt battery. When attempting to open the hood, if hands (or other body parts) come into contact with the rogue high voltage arc, involuntary convulsive reactions can cause personal injury and you will likely be thrown from the vehicle. However, if the HID system has been damaged, the vehicle body itself will not be charged with high voltage, your body must come into contact with the arc. Since the HID output is a low amperage system, the risk of death by electrocution from this system is very low. Obviously, now that you know the facts, care must be taken when approaching the front of any vehicle with HID lighting systems. It is important to know that simply turning the ignition off will not turn off the headlights on most vehicles. They will remain operational until they are turned off at the switch or the 12 volt battery has been disconnected. The 12 volt battery must be disconnected to disable the SRS airbags and this will also disable the HID system. It should be noted that the 12 volt battery may not be located under the vehicle hood. Alternate locations for battery placement is becoming more common, especially on Hybrid vehicles.

As you can see, vehicle technology has advanced to the point where first responder jobs have become more complicated and potentially hazardous. Hybrids, alternative fuel vehicles, SRS airbags and complex body structures are just some of the technologies that can pose complications and hazards when performing a rescue or extrication. Up-to-date training has become one of the most critical tools when dealing with all of these technologies.

Be Safe.

Hybrid Models Around Us Today

Last modified on 2012-03-05 21:02:54 GMT. 0 comments. Top.

by Paul Bindon & Matt Stroud

Hybrid vehicles are becoming more and more common on the road today.  Is the commuter bus next to you in traffic a Hybrid?  In some cities, it certainly is.  The car in front of you may look like a normal car, but in some cases it’s the Hybrid version that uses the exact same body style. Identifying Hybrid models is not as straightforward as it may seem.  Hybrid vehicles pose new challenges to first responders who must be prepared to understand vehicle technology when responding to motor vehicle accidents (MVA’s).  In our last article, we outlined “What is a Hybrid”.  Here we will be discussing the different types of Hybrid systems and models on the road today.  Several different types of Hybrid vehicles have been produced by auto manufacturers to date.  Understanding the differences in these vehicles will help to make critical decisions in the field, saving valuable time when injuries are involved.

Hybrid vehicles exist in several different battery voltages and drive types.   They range from “Mild” Hybrids (36 volt systems) up to the heavy truck and bus systems (800 volt systems). The following will outline the similarities and differences in these systems.

Mid-Voltage Hybrid

Mid-voltage Hybrids were introduced by General Motors initially in their Chevrolet Silverado and GMC Sierra pickups in 2004.  These trucks obtained improved fuel economy by using start/stop technology to shut off the engine during deceleration/regenerative braking and when the vehicle was stopped.  Some reduction in emissions is also achieved as compared to their conventional counterparts.  The number of models increased in 2007 with the Chevrolet Malibu and the Saturn Aura.  2008 saw the introduction of a small Saturn SUV called the Vue Greenline.

Mid-voltage Hybrids use 3 batteries connected in series to produce 36 to 42 volts. This voltage allows the use of a powerful starter motor/generator that is built into the transmission.  Mid-voltage Hybrids use blue wires to indicate wiring that contains 36-42 volts.  The voltage contained in these systems present an increased arc hazard, but do not contain a lethal amount of voltage.  They therefore do not pose the same hazards as full Hybrid vehicles.  Mid-voltage Hybrids can be handled as a conventional vehicle when performing power down procedures.  It must be noted that mid-voltage Hybrids, like all Hybrids, contain a separate 12 volt system which powers all conventional systems including SRS, HID headlights, power windows, etc.  Mid-voltage Hybrids do not contain a high voltage battery, orange wires or a high voltage motor that drives the wheels.

Considered by some to be “mild Hybrids”, these vehicles do not offer the fuel economy improvements or emissions reductions that are possible with higher voltage systems.  They also do not offset the added cost of the Hybrid system over its outwardly identical conventional counterpart.

Full Hybrid

Full Hybrid vehicles are able to use electric motors to drive the vehicle wheels directly, or assist in driving the wheels through a conventional transmission.  They differ from mid-voltage Hybrids because they use battery packs that contain from 100 to 800 volts.  Not only do full Hybrid vehicles use start/stop technology, they also allow the vehicle to store energy that would normally be lost during braking, by generating power that is stored in the high voltage battery.  Significant increases in fuel economy and emissions reduction are possible by using these higher voltage systems.  Since the voltage contained in these systems is over 60 volts, the automotive industry standard orange wires are used wherever high voltage may be present.  All full Hybrid vehicles contain a high voltage battery, orange wires and a high voltage motor(s). Currently, there are three different types of technologies used in full Hybrid vehicles; Series Hybrid, Parallel Hybrid & Series/Parallel Hybrid.

Series Hybrid

Series Hybrids, a type of full Hybrid vehicle, do not have a direct connection between the engine and the wheels.  The engine drives a generator which provides electric power for either the battery (power storage) or the electric motor (driving the wheels).  Examples of this type of Hybrid include the Chevy Volt, full size transit buses produced by New Flyer & Gillig, and heavy trucks produced by International, Kenworth and others.  Increases in fuel economy and emission reduction are made possible by using the engine at its most efficient speed, shutting off the engine when decelerating or at a stop and by charging the batteries during regenerative braking.

Parallel Hybrid

Parallel Hybrids, a type of full Hybrid vehicle, use electric motors to assist the engine in driving the wheels through a conventional transmission. The electric motor is located between the engine and the transmission.  Honda pioneered this technology with the “Integrated Motor Assist” system that was first found in the 2000 Honda Insight.  The Mercedes S400 also uses a motor assist system to help drive a conventional type transmission.  These systems use start/stop technology, motor assisted motion as well as regenerative braking to increase efficiency.

Series/Parallel Hybrid

Series/Parallel Hybrids, the most common type of full Hybrid vehicle, can use the electric motor alone or in combination with the engine to drive the wheels. The drive motor also charges the battery during braking. The engine can also power a generator to produce power for motor use or storage in the high voltage battery.  A/C voltage is used in most vehicles to increase the efficiency of the motor(s).  These systems use start/stop strategy, regenerative braking and the most efficient engine operation speed to significantly reduce fuel use and emissions.

As you can see, Hybrid vehicles vary greatly with different drive types and voltages.  Understanding the differences between Mid-Voltage Hybrids and Full Hybrid vehicles will help first responders effectively evaluate the MVA scene and take appropriate action.

Our next article “Hybrids, Electrical Theory & Circuits” will focus on explaining basic electrical theory and how it pertains to the automobile industry.

What is a Hybrid?

Last modified on 2016-06-06 22:34:00 GMT. 0 comments. Top.

by Paul Bindon & Matt Stroud

Have you ever thought about how you would handle yourself or your crew when dealing with a hybrid vehicle that was involved in an incident?  Maybe you have taken a class.  Did you get enough information from that class to make you comfortable dealing with any scenario?  Did you walk away having questions unanswered?  Even worse, did you walk away with more fear than before the class?  Maybe you have never even thought about it.

This is the first in a series of monthly articles about hybrids and other alternative fuel vehicles, as they pertain to first responders.  Future article topics will include:

  • Hybrids Around Us Today
  • Electrical Theory
  • High Voltage vs Low Voltage Circuits
  • High Intensity Discharge Headlights
  • Parts Location
  • Approach Tactics & Power Down Procedures
  • Fire & Submersion Procedures
  • Myths
  • Airbag Technologies
  • Alternative Fuels & Future Technologies

These articles are designed to provide a complete and in depth understanding of these technologies.  Our goal is to eliminate hesitation and fear when responding to vehicle incidents.

MGS TECH. Corporation consists of factory trained Master Diagnostic specialists with 50 years of combined automotive and engineering experience.  We have also participated in extensive extrication and tactical training courses.  These two fields blended together form the symbiotic relationship necessary to teach the broad range of topics discussed during our new vehicle technology classes.

Let’s begin with some history; Automobiles were powered with electric motors as early as the late 1800’s.  They had the advantage of simplicity over their gasoline counterparts of the time.  There were no difficult gears to shift, they did not need to be crank started and they did not belch smoke into the atmosphere.  They were the preferred method of transportation for the elite when travelling within the city.  The development of better road systems between cities, and the discovery of large amounts of crude oil in Texas in the early 1900’s, caused their limited range and high cost to sway public preference toward gasoline powered automobiles. This preference has continued until the recent resurgence of age old concerns about pollution and dependence on foreign oil that make alternatives more appealing.

From the Congressional Record, 1875;
“A new source of power… called gasoline has been produced by a
Boston engineer. Instead of burning the fuel under a boiler, it is
exploded inside the cylinder of an engine…
The dangers are obvious
. Stores of gasoline in the hands of people
interested primarily in profit would constitute a fire and explosive
hazard of the first rank. Horseless carriages propelled by gasoline
might attain speeds of 14, or even 20 miles per hour. The menace to
our people of this type hurtling through our streets and along our
roads and poisoning the atmosphere would call for prompt legislative
action even if the military and economic implications were not so
overwhelming… the cost of producing (gasoline) is far beyond the
financial capacity of private industry… In addition the development of
this new power may displace the use of horses, which would wreck
our agriculture.”

As you can see, current concerns regarding new vehicle technology being offered today differ little from those expressed at the end of the 1800’s.  New types of fuels and emission concerns are still very relevant.

Social and legislative pressures in the late 80’s led to the federal Clean Air Act and the subsequent adoption of the Zero-Emission Vehicle (ZEV) standard by the state of California in 1990. As a result of these regulations, the major auto manufacturers were required to sell ever increasing numbers of zero emission vehicles in California over the following years, with a goal of 2% by 1998 and 10% by 2003.

General Motors produced a zero emission vehicle called the EV 1 from 1996 to 1999.  The EV 1 was a capable electric vehicle with good range and power.  GM offered it as a lease-only vehicle, leasing only 800 units due to high production costs.  GM claimed it was not able to make enough of a profit on it to justify continued production, thus the vehicles we’re recalled and destroyed.  Ford, Chrysler, Toyota and Honda also offered electric vehicles during that time in very limited numbers.  Since the auto manufacturers were unable or unwilling to meet the zero emission standards established in California, subsequent legal battles resulted in compromises that included; blended gasoline with alcohol as an “alternative fuel”, a new rating system for gasoline powered vehicles’ emission standards, and the production of natural gas and hybrid vehicles as Ultra Low Emission Vehicles (ULEV’s) or Partial Zero Emission Vehicles (PZEV) instead of electric or zero emission vehicles (ZEV).  The byproduct of these emission standards is a very efficient vehicle with exceptional fuel economy; the Hybrid.  Hybrid vehicles became widely available to the public in the year 2000 with the introduction of the Honda Insight.  The following year Toyota introduced the Prius.  An in depth look at the Politics involved in this evolution can be seen in the movie “Who Killed the Electric Car”.

A Hybrid vehicle blends internal combustion engine and high voltage electric motor technology together, to reduce greenhouse gas emissions and increase fuel economy.  Energy is stored in a high voltage battery pack and used by high voltage electric motor(s) to either drive the wheels directly, or assist in driving the wheels through a conventional transmission.

System types include:

  • Parallel hybrids use the electric motor(s) or the internal combustion engine together or individually to power the vehicle. (Toyota Prius Synergy drive)
  • Mid Parallel hybrids use a compact electric motor to assist the internal combustion engine in driving the wheels. (Honda Civic Integrated Motor Assist system IMA)
  • Series hybrids use an internal combustion engine to produce electricity that is either stored in a battery, or used by an electric motor to drive the wheels. (soon to be released Chevy Volt)
  • Hydrogen fuel cell vehicles are also a type of series hybrid.  The fuel cell provides electricity for storage in the battery or for use by the electric motor that drives the wheels.  While there are no production fuel cell vehicles available currently, prototypes from most major manufacturers have been produced (Toyota, GM, Hyundai, Honda etc.)

Hybrid vehicles utilize a regenerative braking to capture the vehicles forward motion and convert it to electricity that is stored in the battery.  Computer controls make this possible by converting the electric motors into generators.  The complexity of these systems has only been made possible by advances in modern computer technology.

With millions of these vehicles on the road today, they are an important part of our transportation system.  Learning how they work and how to safely respond to an incident involving them is an important part of a first responders’ career training.

In Summary, we realize that some of the material presented in this article may be dry.  It is however important that you understand the history of these vehicles and where vehicle technology is heading.

Our next article, “Hybrid Models Around Us Today”, will focus on current hybrid models of cars, trucks, buses and mid voltage hybrids.