Can I Completely Deactivate Airbags?

[rmoore]

A posting by Ron Moore, Moderator

Lt. Fred Hayter of the Corner Brook Fire Department in Newfoundland Canada asked if it possible to "completely" deactivate airbags at crash scenes. Many rescuers have the same wish as the Corner Brook firefighters but I'm afraid there isn't a 100% cure to our loaded airbag dilemma as of yet.

The bottom line is that there is nothing that we are able to do at a crash scene that will "completely" deactivate an airbag system. We can only do things that will reduce the chances of deploying a 'loaded' airbag.

The electrical system of the airbag has one or more storage units called capacitors.
These contain enough reserve power to deploy an airbag for various lengths of time. Capacitors are provided because the car's battery may instantly be destroyed in a crash
and then there would be no way to fire the airbags to protect the occupants.

Capacitors store energy for one second (newer BMWs for example) up to 20 or more minutes. The average stored energy time is about 90 seconds. We refer to the process of the capacitor losing its' energy as 'drain time'.

Once rescuers take away the electrical power at a crash scene, the drain time begins.

Why I say we cannot completely, 100% guarantee that airbags will not activate while we're at the scene is because the units themselves are sensitive to stray or static electric charges. In 1998, Audi recalled airbags because when the driver got in, slid across the seat to get into position, and then touched the steering wheel to drive the car, the static charge fired the driver's bag in their face. 32 times in three months!

Another recall by a different automaker was due to moisture reaching the airbag module and causing the Sodium Azide to react. (Don't do extrication in the rain, I guess!)

So, tell your crew to
1) take away the power as soon as possible, 2) "scan" the vehicle for deployed and
loaded airbags( front, sides, rear and now the roofline)
3) notify all responders close to the vehicle of the deployed or loaded airbag status,
4) be aware of and stay out of the 10"-18"-5" inflation zones of loaded bags,
5) proceed with normal extrication and
medical work realizing the inherent risks involved in our work at the crash scene.

If you can suggest one or two other "bottom line" bullet points to add to these five, please let me know so all may of us may share and learn together.

[Haligan3]

I am reading the book Rescue Technician from the University of Maryland (MFRI) and in the book it states that you can disconnect both the positive and negative battery cables and by touching them together, this will drain all the power from the vehicle.

This is the first time that I ever heard of this. Can you confirm or deny?

Thanks


[Note: This message has been edited by rmoore]

[rmoore]

A posting from Forum Moderator Ron Moore

Haligan3;

I have been told of this 'touching' story many times. It is an Urban Legend and is not true.

For three years back in 1989-1992, one automaker had one model in their line where this technique worked. Since then, vehicles have diodes installed in their electrical systems and the whole idea in now bogus.

The importance of shutting off the electrical power of a vehicle involved in a crash has long been understood by fire, EMS and rescue responders. Headlights and turn signals, radios, heater or air conditioner fans, even
four-way flashers may still be operating when the first due companies arrive at the crash.

Electrical shutdown minimizes the possibility of post-crash fire caused by electrical arcing or sparking and prevents unwanted energizing of any electrical equipment on the vehicle. Most importantly, with loaded
(undeployed) airbags still intact inside a vehicle, once power is shutdown, the airbag system's capacitor(s) begins draining their stored energy. Leaving an electrical system intact while involved extrication work is
underway is how Dayton (OH) rescuers caused the only documented airbag deployment during an extrication in August of 1995.

Modern vehicles have state-of-the-art electronic electrical systems nowadays with semiconductor diodes integrated into the entire system.

Semiconductors are made from material somewhere between the ranges of conductors and nonconductors.Semiconductors, basically, are designed to do one of three things: (1) stop the flow of electrons, (2) start the
flow of electrons, or (3) control the amount of electron flow. A diode is, in effect, a one-way valve. It will conduct current in one direction and remain non conductive in the reverse direction. When current flows
through the diode, it is said to be "forward biased." When current flow is blocked by the diode, it is "reverse biased." Touching battery cables together as the story goes, is the reverse manner. Current will NOT flow. You will NOT drain the airbag capacitors.

So what do I suggest we do with battery cables? Here's my checklist;

• cut negative battery cable(s) first using care not to touch any metal part of the chassis with the cable or your tools, thus minimizing risk of creating a spark

• cut each ground cable a second time to remove a minimum 2 inch section ( if unbolting ground cables at battery terminal, fold cable and clamp onto itself and securely wrap with insulating tape to protect bare cable clamps from establishing a ground)

• check that ALL negative grounding cables have been disconnected from the battery

• assess if there is any evidence that power from the battery is still running any part of the electrical system of the vehicle

• cut positive battery cable(s), also cutting each 'hot' cable a second time to remove a minimum 2 inch section

• check the electrical system again to make sure it is not receiving power.

• if electrical system remains energized after this action, determine location of ADDITIONAL batteries and repeat shutdown tactics for second battery.

Shutting down a vehicle's electrical does not insure that a loaded airbag will not deploy during our extrication. Disconnecting the battery early in our rescue activities is, however, the most effective means of minimizing the potential for loaded airbag deployment. Vehicle rescue is still a gamble against time for both the patient and the rescuer.

By aggressively shutting down the vehicle's electrical system, as professionals, we are simply minimizing the risks.

[Phred]

RON: Re deactivating the vehicle electrical system; your thoughts on:

1) I remember reading an article advocating leaving batt connected until it could be determined if powered windows, door locks or seats should or could be used to effect or enhance the rescue effort. Author suggested NOT cutting cables, but disconnecting them for possible re-connection if required to power up a vehicle system.

2) Once decision is made to deactivate the electrical system, how much labor, equipment, and time to you recommend be put towards reaching and killing the battery? Considerable time & effort are sometimes required to reach a battery if there is heavy front end damage or an overturned situation. Unless there are loaded airbags present, is killing the battery a high priority item? Remember an electrical problem could be causing a slow but dangerous heating condition anywhere in the vehicle.

3) Have you ever re-connected a battery to power something up? It's a situation that I don't think would come up that often, but it would be a real challenge to replace those two 2" chunks of battery cable to move a seat back via power!

4) Now consider question 2 given an airbag equipped vehicle with one or more still loaded bags AND heavy damage requiring force for both victim removal and battery deactivation. Do you delay victim removal in order to ensure killing the battery, or try to do both and hope the bag doesn't fire?

Let's hear some ideas.

------------------
Phred from Ohio
Phred322@aol.com (http://Phred322@aol.com)

[rmoore]

Phred from Ohio asked:

RON: Re deactivating the vehicle electrical system; your thoughts on:

I remember reading an article advocating leaving battery connected until it could be determined if powered windows, door locks or seats should or could be used to effect or enhance the rescue effort. Author suggested NOT cutting cables, but disconnecting them for possible re-connection if required to power up a vehicle system.
============================== ===============
Ron Moore's reply:
I strongly agree that there can be advantages to using a vehicle's electrical power to accomplish certain specific 'interior access' actions at a crash scene. I do feel however that use of an electrical system should be done early in the operation, and should not be done after the battery is shutdown or any involved or heavy-duty extrication work has begun.

Here's my quick mental checklist for electrical system management at a crash scene;

• Stabilize scene hazards; fire, fuel, wires down, hazmat, etc.

• Stabilize vehicle to prevent movement; block and chock

• If determined safe to do so under the circumstances of the crash, and prior to heavy-duty forcible extrication work beginning on the vehicle, utilize vehicle's interior electrical controls for 'interior access' including;
1) unlocking power doors,
2) lower power windows,
3) open rear trunk or hatchback,
4) move power operated seat(s)

• Take away electrical power by disconnecting or cutting negative ground cable near battery. This allows airbag system electrical storage capacitors to begin their "drain" down.

• Secure end of cable with duct or electrical tape to prevent re-establishing contact with any metal components.

• Do not re-establish electrical power to a vehicle once it has been shutdown.

• Remain clear of the inflation zone of all airbags
(Electrical storage capacitors present in an air bag system may allow the system to remain energized with reserve power from 4 seconds to over 20 minutes even though the battery has been disconnected).

• Proceed with normal rescue and EMS activities.

[rmoore]

Phred from Ohio asked another question;

"Once decision is made to deactivate the electrical system, how much labor, equipment, and time do you recommend be put towards reaching and killing the battery? Considerable time & effort are sometimes required to reach a battery if there is heavy front end damage or an overturned situation.

Unless there are loaded airbags present, is killing the battery a high priority item? Remember an electrical problem could be causing a slow but dangerous heating condition anywhere in the vehicle".

Ron Moore's reply:
I believe that shutting down electrical power should remain a high priority at a crash scene even though access to the battery may be restricted. Besides airbags, there are still advantages to shutdown if you are going to do any extrication work. In most situations, there are far more advantages to eliminating power than there is to ripping apart an energized vehicle. All things considered, I'd assign one member or possibly two to the task, telling them don't stop till you accomplish the task.

In your training, you should practice alternative methods of accessing batteries. To train for the rollover situation you mentioned, practice cutting through side fenders or fenderwells for battery access. Also practice reaching a battery from the undercarriage side of a rollover. If you plan ahead, you'll be better prepared for the tough access jobs.

To train for the severe head-on with virtually no access to the battery, practice different styles of entry down through the closed hood, through the fender, or straight through the front grille area as possible alternatives. Be creative. See how many ways you can reach a battery WITHOUT opening the hood.

[rmoore]

Another question was asked by Phred:

"Have you ever re-connected a battery to power something up? It's a situation that I don't think would come up that often, but it would be a real challenge to replace those two 2" chunks of battery cable to move a seat back via power!"

Ron Moore's reply:
If you have shutdown a battery and carried out extrication work on the vehicle (door job, sidewall removal, roof removal, etc), I would not re-establish power to accomplish a task such as moving a seat. In my opinion, we should train and accept the reality that once the power is off, it's OFF! We know we have the ability to accomplish any and all tasks without using electrical power.

Personally, I recommend not moving a seat unless it is unoccupied. Of all the things we can do to a vehicle, an occupied seat is THE part of the vehicle that is directly connected to our patient. I always go into a job with the idea of 'peeling a banana'. The patient is the center of the banana and the damaged vehicle is the skin that I must move or remove to access the core. I'll peel all the skin off the banana and leave the patient alone. I don't like moving seats with injured people on them!

[rmoore]

A question was asked about battery access during tough crash situations. Phred from Ohio asked:

"Now considering the question of how much labor, equipment, and time be put towards reaching and killing the battery, given an airbag equipped vehicle with one or more still loaded bags AND heavy damage requiring force for both victim removal and battery deactivation. Do you delay victim removal in order to ensure killing the battery, or try to do both and hope the bag doesn't fire?"

Ron Moore's reply:
Depending upon circumstances, especially degree of patient entrapment and medical status of the patient, I would NOT delay extrication work nor would I delay moving the patient out of the vehicle just because the airbag is loaded and the electrical system is "hot".

Remember the Dayton Ohio incident. Realizing the risks inherent with what we are doing, as a rescue officer, I would remind all personnel directly involved of the location of loaded airbags and quietly remind them to use extra caution staying out of the airbag inflation zones.



[Note: This message has been edited by rmoore]