BTB (Back To Basics)- Disconnecting a Car Battery

[waterboy1]

When you remove the negative cable first you will get NO sparks while removing it.(wrong) If you remove the positive cable first you WILL get sparks just from removing it as it is still in a closed circut. Also there is some mis-information in a few of the above threads....Regardless if the negative cable is removed or not, IF you touch any metal part with your wrench while removing the positive cable, you will get sparks. You are creating a dead short between the positive and ground.(Wrong again)

First, if there is any draw on the battery, both the + and - will spark.
Second, if the - cable is removed then there is nothing to complete the circut.
Nice try though.

[firefighter105]

Airbags are more likely to be triggered if you disconnect the positive first. Neat show, but not fun.

At least that was what i was told in my lessons on vehicle extrication.

[mark440]

I've always been taught and practiced and taught to disconnect the ground cable first.
Now as to the question of cutting or disconnecting, I have tried to make it a habit to always disconnect, not cut the ground cable. The reasoning: One day a nice lady (who happened to be a dispatcher of ours) was pulling through the local bank ATM when she did not see the bright yellow 4' high barricade that would prevent her from running into the side of the building. Brand new Ford F-350 powerstroke crew cab. Took the pillar right on the blue oval. Major fluid leak. No injuries, minor crash. Fixable by many opinions. The engine crew (young crew, no experianced officer supervision, volunteer crew) CUT 2" out of the cables while they mitigated the fluid leak.
Nicely disabled, good job fellas! But the truck just needed a new hood, new grill and a couple of whapps of the hammer and bammo! Brand new truck again! Except for the $400 the autobody shop charged the insurance company for new cables and labor.
Needless to say the insurance company reviewed our SOP's and wished reimbursment from the VFD for the amount of approximately $400.

Someone has already said TRY BEFORE YOU PRY. Use some common sense and think before you do some of the things we do commonly.

As for cutting, there are just certain times you NEED TO CUT! Extrication (not extended) is a cuttable instance. Life before property.

Batteries are spread out all over. My wifes 2005 Chevy Tailblazer has a battery under the back seat. Wouldn't have known that if not for an astute observation by her extremely curious husband!

*Mark

[RESERVEFORNOW]

Let's go a step further. Do you disconnect the battery cables or cut them?

Are you assuming no life threatening injuries with this question?

[Frmboybuck]

My point was that just because the negative is "unhooked", that dosent assure you that NO sparks will fly. I was not assuming there was draw on the battery either but in that case then yes you will get sparks from either cable because you have current flowing and you are breaking the chain

[SIGNAL99COM]

It looks as if everyone here is smart enough to know when to cut and when to disconnect. The point I wanted to get across was if I am inside the car working on the patient, I want the battery disconnected as soon as possible. I do not want to see a minutes pass because the crew is screwing around with wrenches, trying to find the correct size so that they can disconnect the battery from the terminals. Get the damn cutters and have them cut within seconds. Some airbag systems take a while for them to deenergeize. I do not need the damn airbag going off in my face while I am applying a collar, KED, etc.

As for price of new battery cables, for most vehicles, they are not expensive. For example, the cables for my '05 Impala are $12 a piece. Most cost between $10 and $20 a per cable.

[nmfire]

When you remove the negative cable first you will get NO sparks while removing it. If you remove the positive cable first you WILL get sparks just from removing it as it is still in a closed circut. Also there is some mis-information in a few of the above threads....Regardless if the negative cable is removed or not, IF you touch any metal part with your wrench while removing the positive cable, you will get sparks. You are creating a dead short between the positive and ground.

Not sure where you came up with this information but it is all incorrect and you clearly don't know how electricity works.

You will get sparks from either cable when you pull the clamp off. The more things in the car that are turned on, the bigger the sparks will be. I've found that cutting it slowly tends to make little or no spark. Unclamping it always makes sparks if there is a load on it.

If the battery negative/ground is disconnected, touching the tool from the positive terminal to the body or anything else will do absolutely NOTHING. You can lick the battery post and touch the metal body with a bleeding hand and nothing will happen. There is no circuit to complete and the body has no electrical connection to anything.

What others have said about why we take the negative/ground first is absolutely correct. It won't make a difference to the airbag system which you diconnect first. Neither make it any more or less likely to fire.

What about Hybrids???

A hybrid vehicle is exactly the same as a conventional vehicle as far as the 12 volt system and airbags. Disconnect just like you would any other vehicle.

The differences are in how you de-energize the high voltage system. Some high voltage systems disconnct when the 12 volt system is disconnected. Some require you to find a disconnect switch in the trunk. Some have a delay. The high voltage wires will be big bright orange, red, or blue wires. The wise fireman would make an effort to not touch them. In fact, the ERG for most hybrid vehicles state that rescuers should remove all jewlery before entering the vehicle to avoid dangling things from touching the wires. Most of the HV systems have a safety that will disconnect it automaticly if it senses a fault. However, keep in mind that the electric motor is a significant load, probably more than your hand so it may not see a person as a fault.

[Frmboybuck]

Not sure where you came up with this information but it is all incorrect and you clearly don't know how electricity works.

You will get sparks from either cable when you pull the clamp off. The more things in the car that are turned on, the bigger the sparks will be. I've found that cutting it slowly tends to make little or no spark. Unclamping it always makes sparks if there is a load on it.

If the battery negative/ground is disconnected, touching the tool from the positive terminal to the body or anything else will do absolutely NOTHING. You can lick the battery post and touch the metal body with a bleeding hand and nothing will happen. There is no circuit to complete and the body has no electrical connection to anything.

What others have said about why we take the negative/ground first is absolutely correct. It won't make a difference to the airbag system which you diconnect first. Neither make it any more or less likely to fire.




A hybrid vehicle is exactly the same as a conventional vehicle as far as the 12 volt system and airbags. Disconnect just like you would any other vehicle.

The differences are in how you de-energize the high voltage system. Some high voltage systems disconnct when the 12 volt system is disconnected. Some require you to find a disconnect switch in the trunk. Some have a delay. The high voltage wires will be big bright orange, red, or blue wires. The wise fireman would make an effort to not touch them. In fact, the ERG for most hybrid vehicles state that rescuers should remove all jewlery before entering the vehicle to avoid dangling things from touching the wires. Most of the HV systems have a safety that will disconnect it automaticly if it senses a fault. However, keep in mind that the electric motor is a significant load, probably more than your hand so it may not see a person as a fault.

I clarified my statement in my post above.....Atleast to some I did

[Ron3427]

Why are we cutting them in the first place? Has anyone been to an extrication competition and done this? Can you tell me what hazards are being overcome by doing this? And I don't wanna here back air bags unless your ready to explain how they work and why it would be advantagious. I can only think of a very few rare instances where you would need to disconect the juice and none of them apply to our everyday pin jobs.

[nyckftbl]

Why are we cutting them in the first place? Has anyone been to an extrication competition and done this? Can you tell me what hazards are being overcome by doing this? And I don't wanna here back air bags unless your ready to explain how they work and why it would be advantagious. I can only think of a very few rare instances where you would need to disconect the juice and none of them apply to our everyday pin jobs.

Wait, you're basing your assumptions on extrication competitions?

[Bones42]

Why are we cutting them in the first place?

Very simple...to de-energize the vehicle. Why would you not?

[KenNFD1219]

Just to make it more confusing, remember that electricity flows from negative to positive. Electrons have a negative charge and accumulate on the negative plate of the battery. They flow through the conductors and load to the area of electron deficit at the positive side of the cell.

Two atoms are walking down a street. One says "I think I lost an electron" The other says "are you sure", the first replies, "Yes, I'm positive".

Think of it this way, the negative wire connects to the car body and frame and fills it with electrons. The positive side (red wire by convention) provides a drain for the electrons to travel back to the other side of the battery, in essence, to balance the chemical reaction occuring in the battery. In the old days, with metal dashboards, you could install a stereo and only hook up the positive wire to the fuse block. The negative supply came through the mounting hardware to the chasis of the radio.

The negative lead coming from the battery, if it comes in contact with the body, can re-energize the vehicle.

Cutting any conductor under a load will produce an arc as the electrons try to contiune flowing. The size of the arc is a function of the current drawn, not if the lead is positive or negative. Placing an ammeter on either the positive or negative side of a load will indicate the same current draw.

If you were to cut the negative cable and then connect a voltmeter to the two ends, the cable going to the ground (frame or body) would now be postive while the wire from the battery would remain negative.

[NYSmokey]

Why are we cutting them in the first place? Has anyone been to an extrication competition and done this? Can you tell me what hazards are being overcome by doing this? And I don't wanna here back air bags unless your ready to explain how they work and why it would be advantagious. I can only think of a very few rare instances where you would need to disconect the juice and none of them apply to our everyday pin jobs.

Uh...to lessen the chance of fire

[nmfire]

Why are we cutting them in the first place? Has anyone been to an extrication competition and done this? Can you tell me what hazards are being overcome by doing this? And I don't wanna here back air bags unless your ready to explain how they work and why it would be advantagious. I can only think of a very few rare instances where you would need to disconect the juice and none of them apply to our everyday pin jobs.

Are you serious? First of all, this has nothing to do with extrication. It should be taking place at any minutely serious MVA. The hazzards are the same regardless of the doors being pinned shut or not. And the fact that you are more or less comparing this to a game shows you simply are not qualified to be making these statements.

First and foremost is it beings to disarm the airbag system... and that is all the airbags, not just rear airbags. I don't even know where you came up with that. Once the battery is disconnected, the airbag computer's capacitors will start to drain. Within 5-12 minutes or so, the airbags will be disarmed and unable to deploy. If you are actually too blind to understand why we do this, I will explain it. It is so they don't go off while we are working on the car and hurt us or hurt a patient. The car is damaged and things are not intact the way they used to be. Relying on the integrity of the sensors, computer, and wiring to not deploy the airbags is simply not reliable. Plus, we are cutting, bending, pushing, and breaking things all over the car. This increases the likeliness of us triggering the system to fire. All of the above has happened before, will happen again, and causes serious injury each time. Cars are being rolled out with airbags coming out of everywhere, even the cheap cars. There are now dual-stage bags that can fire more than once. Some are using 4000psi compressed gas cylinders. Some are using pyro charges. Dealing with airbags and other safety systems is a fact of life for any MVA today and pretending it isn't a problem is simply ignorant.

Second of all, it reduced the risk of a fire. Once again, the car is all mangled up which means the wiring is all mangled up. What happens when you mangle wires and they short circuit to the body? They can easily melt and catch fire as we are cutting, bending, pushing etc. It also ensures that no loose wiring is going to create sparks and ignite leaking fuel.

It also ensures the engine is not going to start. It also ensures that no short circuit of the primary wires leading off the battery will make the battery explode in our faces and/or start a fire. It also ensures the fuel pump won't be running or start running. Electric seats pedals won't start moving on us when we don't want them to.

So, should I keep going, or are these reasons enough?

[FTMPTB15]

Why are we cutting them in the first place? Has anyone been to an extrication competition and done this? Can you tell me what hazards are being overcome by doing this? And I don't wanna here back air bags unless your ready to explain how they work and why it would be advantagious. I can only think of a very few rare instances where you would need to disconect the juice and none of them apply to our everyday pin jobs.

SEE nmfire's post above.. he went into more detail than me!

Thanks.. nmfire!

[Rescue101]

99,Not to "pick"on you but I doubt you are buying a positive cable for your GM thru GM for $12.Negative maybe.And your particular GM is HARDLY representative of some of the late models,particularly imports and their relative parts.Either that,or give me the name of your supplier,we could probably do business.Anyway:when possible I prefer to unfasten the cable and tape it back as some others have indicated.To do this I like to carry a small pair of Visegrip pliers.They work on 99% of the vehicles out there.Plus as a tow operator l find that most modern vehicles have shift interlock to keep you from shifting out of park without the brake applied.Now MOST disengage when battery power is removed but some don't.Any of you who have taken a winching course probably remember what happens to the resistance when the wheels don't roll.And when you take that 2" chunk out of the cable........Weeeeell,you get the drift. One more thought to ponder(these last thoughts are for thought and NOT directed specifically at 99)The more difficult you make it for the tower,the longer it will take to clear the scene.Particularly if you do NOT have a highly skilled operator.Everybody has to work together and it's a VERY GOOD idea to train together. I'm with the majority here,secure the electric as soon as possible.But there are better ways to do it and they vary by vehicle.Learn as much as you can,maybe make a "field trip" training to a local salvage yard. T.C.

[cityfire7]

Take a look at the link that I have here. You will find some really good info on battery locations/discharge times for specific vehicles as well as some good videos.
http://www.sceneoftheaccident.org/
One of the videos is a prime example of why we secure the power. Check out the Dayton Incident (fifth video down). Two Brothers proved how important securing the power can be. (Caution: Large video file)

[NYSmokey]

nmfire,

Great post. Some people just don't get it which makes it dangerous for the rest of us. I carry a $10 of wire cutters in my gear and they are very effective. I cut the cable so that it would be physically impossible for it to reconnect.

Rescue101,

I hear your point and on a very minor mva without injuries I might consider it. Whatever ensures the fastest, safest option for my crew and the patient is what we are going to do.

As for airbags, the auto industry is making it harder for us to do our job. Some of the new capacitors will stay energized for 2-3 times as long as the old ones. Airbags are all over the car. Watch out for knee airbags in the KIA's.

I wish that the auto industry would come up with a low tech/low cost universal key/device for the fire service to completely shut down the airbag system every time. When the cops bust a chop shop with air bag charges present, they call in the bomb squad. Where does that leave us?

[voyager9]

Once the battery is disconnected, the airbag computer's capacitors will start to drain. Within 5-12 minutes or so, the airbags will be disarmed and unable to deploy.

Is this still true? Someone the other day mentioned that while this was true for first-generation air bag systems, most modern systems discharge within 10-15 seconds. I haven't have a chance to look more into it, just something that came up in conversation.

Also, in addition to battery location another complication is battery orientation. Sometimes the battery terminals are burried UNDER the battery, on the side, rear, front. A lot of times there is so much other junk covering the thing that it's impossible to get at with either a wrench or cutters. I wouldn't be surprised if some ingenious auto engineer thought it'd be a good idea to put the terminals inside the battery!

[NYSmokey]

Take a look at the link that I have here. You will find some really good info on battery locations/discharge times for specific vehicles as well as some good videos.
http://www.sceneoftheaccident.org/
One of the videos is a prime example of why we secure the power. Check out the Dayton Incident (fifth video down). Two Brothers proved how important securing the power can be. (Caution: Large video file)

Great video. Recommended for ANYONE who responds to these types of incidents...cops, firefighters, EMS, and tow truck operators.