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MVAs and Cutting Battery Cables.
What is your department's protocol on cutting battery cables on an MVA scene. I know that if you're doing cutting and extrication, it's a no brainer.
However, what about the BS call when there's minimal damage to the car and the person is complaining of neck and back pain? In order to remove the person, we have to put personnel inside the vehicle. Should we take the extra step to cut the battery cables even on a fender bender? Is it safe to put personnel inside the vehicle with undeployed airbags? What are your thoughts?
Replies to This Discussion
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Permalink Reply by Spanner 122 on
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We never "cut" the cables, but I am assuming you are referring to removing the contact from the battery. We do it any time the vehicle is inoperable. If it has to be towed, we take the battery connections, unless the tow company for some reason needs power to the vehicle. If they are delayed, we take the connections, not cutting them means you can simply re-connect if necessary.
If you simply remove the contacts, no matter what the call, you can always put them back. Never cut a battery cable unless it's your only option (and in this case, the vehicle is usually a write off anyhow).
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Permalink Reply by John on
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Every situation is different and depending on how bad the fender bender is we may not disconnect the battery, But of course we will try to un hook the battery whether, rarely do we just cut the cables, unless its that bad to where we cannot reach the connection bolt/clamp. The ultimate decision for us is by command, if they determine the cables need disconnected then we un hook them.
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Permalink Reply by lutan1 on
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We NEVER cut cables.
Disconnect only.
I've had a few MVA's where we've reconnected the power under a charged line protection, so as we can move electric seats, etc
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Permalink Reply by Kevin Hatfield on
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I agree ... it is important to disconnect the battery to protect against ignition and SRS (airbags) if I am able to disconnect the cables without cutting them I do, but at the same time if I am unable to get at the posts I will cut them.
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Side post batteries are sometimes difficult to disconnect when the vehicle is involved in a front end collision, most times you can wedge them off with a tool. I know the tow truck driver appreciates being able to hook the battery back up.
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Permalink Reply by FETC on
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Well Adam I can say, I have actually seen them go off without a battery in the engine compartment.
http://www.firefighternation.com/forum/topics/brain-teaser-air-bag?...
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Permalink Reply by michael smid on
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nowadays we just disconnect,not cut,alot of the times you can push on a sidepost and work it loose
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Permalink Reply by M.J. 6821 on
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I have two thoughts on this. First off on most new cars the airbags have a capacitor that holds juice for anywhere from 1 minute up to to 4hrs it just depends on the make of the car.
2nd if the damage is anywhere on the car where there are airbag sensors I think it is a good idea to cut the juice whether it be cutting the cables or removing the post, my reasons being with all the new metals that are out there and bumpers with gas loaded shocks you never know what might happen. I have towed cars that were minor fender benders and have had airbags deploy as Im winching them onto the flatbed.
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Permalink Reply by David Clark on
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I believe battery cables should be disconnected as soon as possible, even on most minor fender-benders. The reason I think so comes from personnel observation and a little bit of thought regarding vehicle wiring systems.
First the observations... I was an auto mechanic for many years. One day we had a mid eighties pickup parked in the shop. Nobody was in it, the doors and windows were closed, the key was shut off, and it had not been running for quite some time. I just happened to be looking in the direction of the truck when something shorted out inside the cab. In less than a couple of minutes the cab was full of flames and it was well involved. We opened the hood to disconnect the battery and put out the interior with fire extinguishers before the fire department arrived. However disconnecting the battery and extinguishing the fire are not my main point here. My point is how quickly it went from nothing to well involved in such a short amount of time. When an electrical fire starts in a vehicle it can accelerate very rapidly as long as the battery is connected, almost like gasoline is being thrown on the fire; and here’s why.
There are many circuits in the average vehicle and some of them maintain a live feed from the battery even when the key is off. If you take a look at a vehicle wiring harness you see that there are many wires for various circuits run within the same tightly packed wiring loom. When the manufactures design the wiring systems they usually run as many circuits as possible within the same harness to minimize installation costs. This means that if a circuit shorts out for whatever reason and the circuit breaker or fuse does not remove power from that circuit, a wire, or wires within a harness can overheat enough to melt the insulation of the affected circuit as well as adjacent wires to other circuits. As other circuits are then shorted out they too can melt and burn additional wiring. As long as the battery is connected the process can multiply with more circuits throughout the vehicle shorting and becoming powered, usually with much more amperage than they were designed for. Have you ever launched a model rocket by hooking a battery across a nichrome wire? The exact same principle is at work here. It’s helpful to remember two things; a) electricity travels at nearly the speed of light, and b) there is enough power in the average battery to weld ¼-inch plate steel.
Wiring harnesses run throughout the entire vehicle and it is possible that even a minor fender bender could crush, or destroy a wiring harness. Chances are however that if it’s a minor fender bender you will most likely be able to get at the battery fairly easily to disconnect the cables with a wrench or pliers. Removing the power from the battery will go a long way in keeping that minor fender bender from escalating into a vehicle fire. But use your head, depending on the location of damage and your ability to assess the extent of damage the risk might be low. Vehicle wiring systems are generally pretty robust and don’t normally present problems. It is when they have been compromised, such as through collision, that they become vulnerable to shorts. Once wires lose their insulation, through crushing, or fire, etc. then fire can develop rapidly and spread as if an accelerant were involved. In this case the accelerant is electrical energy from the battery.
Having laid out the rationale for disconnecting the battery, the old adage used in extrication “try before you pry,” is still relevant here. If you have access to the negative battery cable and have the means to remove it quickly and without causing sparks then go ahead. If you do not have access to quickly remove the cable with a wrench, or some other conventional means that won’t create sparks then cut the negative cable. I carry a pair of cable cutters in my turnout pocket to quickly remove power from all circuits even if access to the battery is restricted. Always remove the ground cable first to avoid making sparks. In most modern vehicles the negative cable is the ground. Vehicles used to have positive ground systems but that changed for the most part during the late fifties.
I’ve also been in the situation where I couldn’t even get to the battery cables with cable cutters. That is when extreme caution is needed. Having someone standing by with a charged line becomes a lot more critical.
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Permalink Reply by John Dobson on
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If it got to be towed we cut it. If it can be drove we don't.
As far as airbags cutting the battery may have no effect on the airbag system. Remember 5-10-18 rule.
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Permalink Reply by Ben Waller on
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If a car is going to burst into flames, it will generally do so before the 911 call is made.
I've responded to thousands of MVAs in my 35-year career, and have seen exactly two vehicles catch fire after the initial units arrived.
Both were extinguished in seconds with minimal effort.
Both already had the battery completely isolated.
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Permalink Reply by Jody Thomas on
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The hybrid battery is turned off when the ignition key is shut down, the computer senses an airbag deployment, or if the main cable is severed it has a ground fault circuit that kills power to the battery. The disconnect switch is mainly for the repair shops doing service on the unit.
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