Here is a link to a topic seldom mentioned, the fire hazard posed by stored batteries. The 9 volt rectangular batteries used in smoke alarms, digital meters, and toys are a risk for starting fires because of having the positive and negative terminals closely adjacent on the same end of the battery. If the terminals come into contact with paper clips, other batteries, or metal items, they can generate enough heat through the short circuit to start a fire, as in the case of the house fires cited in the linked article. Others like 6 volt lantern batteries (with spring terminals close together on top) pose similar fire hazards.

http://ehssafetynews.wordpress.com/2012 ... -the-rise/

PC

I had one in my pocket once and it shorted across my car keys. They do heat up!

a 9V battery and some steel wool is one of several methods they teach in Boy Scouts on starting a fire while camping. Works a lot faster than a bow drill too.

My favorite method to start fires without matches: easy, simple, starts working immediately. Just don't carry the 9 volt next to the steel wool. I know someone who learned that the hard way.

We have to recycle batteries at work. The 9 volt and 6 volt batteries (from the exit lights) get their terminals well taped up before going in the battery recycling bucket.

I learned that the hard way as a rookie signal maintainer trying to clean the contacts on a crossing gate mechanism. Not one of my brighter moments, but I hadn't figured steel wool would be so flammable.

Almost any battery is capable of developing a fire hazard if shorted. I once dropped a CR2032 lithium cell into a can of mixed hardware and didn't notice it until just a few minutes later the cell exploded with quite a bang and threw sparks around for several feet. It had shorted on some brass screws.