Quote:
Originally Posted by DampRobot
I've heard my electronics friends joke many times that despite all the fuss FIRST makes about battery spills, they essentially never happen.
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Never is perhaps a poor choice of words. Rare yes, Never no!
I've been involved with FIRST teams, competitions and workshops 15 years.
*** SAFETY FIRST ***
1. Most frequent problem is SHORTED Battery terminals or cables bypassing 120A circuit breaker via robot frame or mechanism pinch cut thru taped terminals or heavy wire insulation, causing local &internal overheating =smoke
ref: Team 362 at ATL CMP a few years ago.
2. Battery pierced by sharp conductive on-board or another robots mechanism (aluminum/steel) bypassing batteries over-current protection plus acid leak
Battery sides are very thin, pierced easily, shorted cell bypasses cell to cell fusible link creating instant local heating up to ~1000 amps, enough to melt plastic case and metal that pierced it -- aluminium, copper & Pb.
Like solder,
if molten metal spews on human skin, it sticks.
unfortunately
It won't shake off!!! it is pretty much an instant bond.
Biggest molten threat is working in pit, competition queue line & robot shop:
screwdriver or other metal tool falls across battery terminals:
keep both Batt term mtg's fully covered even double insulated, always wear safety glasses. Eyes are especially vulnerable & irreplaceable
Caution:
Wiping only smears molten metal over a larger skin area. Permanent scarring is unavoidable. Molten metal will penetrate most common clothing instantly.
Possible additions to emergency kit:
Thicker non synthetics hold up best like welding gloves & aprons
Heavy sturdy cloth to wrap battery especially if it's hot, even if it's not
Heavy duty Fireplace log scissors to handle hot battery at safer distance
Burn ointment (heat & neutralize acid), impact activated coolant packs
#1 occurs when robots get vertical (ref: this years ramp), or tumble and battery bounces around inside due to ineffective battery straps. Velcro should NEVER be used as sole heavy battery support. Velcro is better used to hold a rigid 3 point Z-shaped material (top part overlaps battery edge, one could be the rectangular block in this years kit, but needs supplemented with hard overlapping case stops to prevent impacts from popping battery up off block breaking 1/2"W Velcro loose from full weight + leverage.
Best strap and one I recommend is snap action web belt such as used on grocery carts for child restraint, back packs, etc. 2 straps =best (safe 2nd)
Smoking, Pierced, Leaking SLA Battery Summary:
Fear here is good. No one wants or should approach a smoking Batt situation.
Heated acid contents even bound in AGM, Absorbed Glass Mat still represent great danger. (AGM uses less liquid acid & less free than flooded liquid types)
Knowing a pressure valve should vent &/or fusible Pb cell interconnects should melt open around 800-1000A (if short lasts long enough) should not lead to a false sense of confidence that such a Batt is SAFE or adequately "protected".
An internally shorted fully charged battery could remain hot a long time.
Immersion in tub or flush with water &treating diluted solution may be safest
i.e. treat cause of heating most quickly (acid dilution and cooling)