# Fire at PNW, Details please

As to electrocution hazards of a 12 volt battery. Under most circumstances, this will not be an issue. Please remember that the GFCI protectors are specifically designed to sense and open under currents that would trigger a cardiac event. Those are tested to open at 4-6 ma currents.
While the body has skin resistance, the skin acts as an insulator to the tissue inside. 12 volts is not likely to pass into the tissue and the lower resistance path so it can be contacted by the fingers and not produce any noticeable effects. However, everyone knows that holding a 9 volt battery to your tongue will produce some nasty reactions if fully charged. Your tongue is wet, very conductive and does not have the insulating properties your fingers do. However, once the voltage reaches a point where the insulation breaks down, you will feel the effects of the current to some degree as it passes into the tissue below. Contacting the 48 volts on analog phone lines will give me a tingle. To compare, the 110 volts AC at the outlet in your pit is actually 280 volts peak to peak. That will easily overcome any skin insulation and pass into the underlying tissue with ease.
As pointed out in this thread, the battery still has a lot of energy stored inside. Do not work around the battery with dangling jewelry or large tools. The available current is capable of welding metals. It will also break bones if dropped on your foot or your finger.
No matter the source, battery or wall, treat all electricity with respect. If you don’t it will slap you when you least expect it.

*Consider a sine wave with a peak-to-peak
amplitude of 1 unit. It has the equation:

y = (1/2)*sin(x)

The integral of the square of y
over one full cycle is given by:

integrate(y^2,x,0,2*pi) = pi/4

The average value of y^2 over the cycle is:

(pi/4)/(2*pi) = 1/8

The RMS value is given by:

y_rms = sqrt(1/8) = 0.35355339059327

Therefore, a sine wave with an rms amplitude
of 110 units has a peak-to-peak amplitude of:

110/y_rms = 311.12698372208

Battery post driven into cell shorting it bypasses fuse link safety of multi cell batt resulting in >1000A current, melting lead which could spurt Once on skin a serious burn results like solder only worse due to mass of molten lead does not wipe off skin/living tissue instead buries itself deeper into tissue… If in eye… sight could be lost as Molten Lead will melt thru plastic lens like butter… consider using better “Glass” safety lens. Inhaled fumes from burning electrolyte mixing with chemicals from extinguisher mixture could be quite hazardous. Explosion is possible before and after extinguisher is used so carefully consider proximity when examining fire especially in battery (FTA and field crew responders)

The sidewalls of our batteries are very thin… a consideration in mount as any piercing produce equal danger as it bypasses all current limiting (limited only by ‘R’ of Low ‘R’ conductors, lead / aluminium, and cautionary reminder: P=I^R so R is worst for heating when non zero!!! say 1000A^2 * .1 ohm even 100A^2*.1 =10kW! for some short period of time)

Apply lesson learned… Post photo of vaporized melted Negative Battery Terminal – Pic is worth thousand words!

The likely explanation here is that CO2 fire extinguishers are vastly more expensive than a standard ABC extinguisher. The average ABC extinguisher will set you back \$20-\$30, but even the cheapest CO2 extinguisher runs over \$150 (and many are closer to the \$300 range).

Obviously this is a drop in the bucket compared to the cost of an FRC robot, but I suspect many teams and/or events either don’t know the difference between extinguishers, see the price and go into sticker shock, or some combination of both.

There is also the question of priorities; If the priority of the field staff is to protect the field/venue/people from damage/injury, then the onus of preventing a robot from being damaged by a fire extinguisher falls on the team, who should have built the robot in such a way as it wouldn’t catch on fire in the first place.

Yep. I should see if I still have the picture of one team’s battery I pulled the whole positive terminal right out of the battery probably because of those lugs getting hung on something.

I have two in my service truck right now from a non first application where the connections got hot and deformed the top of the battery around the epoxy potting.

**Arizona Teams **
Any teams attending AZ north or west can always come by the 498 pit if they want to use the correct crimper, we’re more then happy to help improve your battery connections.

I had this discussion with a friend that engineered backup battery systems.

Another thing to consider with batteries - unlike outlets at the wall (that will have 10’s to 100’s of feet of wiring from the transformer), the amount self inductance in the circuit is usually much much closer to zero. Meaning that the short circuit current available is almost instantaneous, and the peak power that can be dissipated in a short circuit is much much more.

Batteries are scary things.