Setting Aside a Battery Charging Area

Why this matters

A modern shop charges dozens of batteries: drill and saw packs, work lights, a press tool, maybe a walkie stacker or floor scrubber with a big lead-acid battery. Charging happens wherever there is an outlet, often on a wooden bench under a shelf of cardboard boxes, often overnight with nobody in the building. A lithium pack that goes into thermal runaway on that bench starts a fire that is burning well by the time anyone arrives in the morning. A lead-acid battery charging in a closed corner fills the ceiling with hydrogen. One designated spot, built for both, removes most of that risk.

Two batteries, two different hazards

Lithium-ion tool packs. The hazard is thermal runaway: a damaged, defective or abused cell heats itself, vents flammable gas, ignites, and spreads heat to the cells beside it. The heat-producing reaction inside the cell does not need oxygen from the room, which is why a pack fire is hard to put out and can reignite after it looks finished. Packs most likely to fail are the ones that were dropped, crushed, soaked, overheated in a truck, swollen, or charged on a charger not made for them. The cell chemistry and the van and customer-equipment side are covered in Lithium-Ion Batteries in Tools, Vans and Customer Equipment; this card is about the spot in the shop.

Flooded lead-acid equipment batteries. The hazard is gassing and electrolyte. Near the end of a charge, and especially during an equalize charge, a flooded battery releases hydrogen and oxygen. Hydrogen is flammable from about 4 percent in air, and it rises and collects at the ceiling. The electrolyte is sulfuric acid, which burns skin and eyes, and it gets out when a battery is overfilled, tipped, or watered carelessly. Sealed lead-acid batteries gas far less in normal service but still vent if overcharged.

The layout has to handle both: fire containment for the lithium side, ventilation and acid response for the lead-acid side.

What OSHA asks of a lead-acid charging spot

Where the battery powers a forklift, pallet jack, walkie stacker or other powered industrial truck, 29 CFR 1910.178(g) sets the requirements for the employer. In substance:

• A designated area. Charging installations are located in areas set aside for that purpose, not wherever the truck happens to stop.
• Flushing and neutralizing. Facilities for flushing and neutralizing spilled electrolyte, meaning water and a neutralizer such as a baking-soda-based spill product at hand.
• Fire protection at the charging area.
• Protection of the charger from damage by trucks, which in practice is a guard or bollard and a charger mounted on the wall, not on the floor.
• Ventilation adequate to disperse fumes from gassing batteries.
• No smoking in the charging area, and precautions against open flames, sparks and electric arcs.
• Acid into water. When electrolyte is mixed, acid is poured into water, never water into acid.

Separately, 29 CFR 1910.151(c) requires suitable facilities for quick drenching or flushing of the eyes and body within the work area wherever a person's eyes or body may be exposed to corrosive materials. That reaches the person watering a floor scrubber's battery too, even though a scrubber is not a powered industrial truck and 1910.178 does not reach it. A plumbed eyewash is the reliable answer; a self-contained eyewash station is acceptable when it delivers the flushing the standard and ANSI Z358.1 describe, and it is checked weekly.

Anyone watering or handling flooded batteries wears chemical splash goggles with a face shield, acid-resistant gloves and an apron, chosen under the shop's 29 CFR 1910.132 hazard assessment. Batteries are watered after charging, not before, because the electrolyte level rises during charge and an overfilled cell boils acid out of the vent.

What a lithium charging station needs

No OSHA standard is written for tool-pack charging. The controls come from the charger and pack maker's instructions, the fire code's general rules on electrical equipment and combustibles, and common sense about where a fire would go.

• A noncombustible surface. A steel shelf or bench on a concrete floor, with gypsum or masonry behind it. Not a wooden bench, not on top of a cardboard box.
• Clear space. Keep combustibles at least 3 feet from the charging shelf as a shop default: no boxed stock, rags, paper, or the trash can. Nothing stacked on top of the chargers, which need air to cool.
• The maker's charger only. A pack charges on a charger listed for it. A cheap substitute charger is a common cause of overcharge.
• Smoke or heat detection above. A detector over the station, tied to the building's monitored alarm if there is one. In a dusty shop, ask the alarm contractor whether a heat detector suits that spot better than a smoke detector.
• A quarantine bin for damaged packs. A metal container with a lid, holding dry sand or a product made for battery quarantine, away from the charging shelf. A swollen, cracked, crushed or wet pack goes in it and is never charged again. It leaves the shop through a battery recycler.
• Charging timed to occupancy where practical. A charge that finishes while people are in the building is one someone can see go wrong. Where packs must charge overnight, the detection above becomes the control that matters.

The layout

  EXTERIOR WALL                  [EXHAUST FAN, HIGH]
 +-----------------------------------------------------+
 | [SMOKE/HEAT DET]               LEAD-ACID CHARGER    |
 | STEEL SHELF                    wall mounted,        |
 | tool chargers, 1 per outlet    own circuit          |
 | nothing stacked on top         [WALKIE parks here]  |
 |                                [BOLLARD] [BOLLARD]  |
 | 3 FT CLEAR: no boxes or rags   EYEWASH, NEUTRALIZER |
 |                                NO SMOKING sign      |
 | [METAL BIN, LID, SAND]                              |
 | damaged or swollen packs only                       |
 +-----------------------------------------------------+
   aisle side: no exit door, no electrical panel here

The lead-acid charger sits under the high exhaust point because hydrogen rises. The lithium shelf and the quarantine bin are on the same wall but not touching, so a pack fire in the bin is not beside the packs on charge. The exit door is elsewhere, so a fire at the station is between nobody and the way out.

The fire code layer

The fire code as your jurisdiction adopted it reaches the charging area too. In the 2021 IFC, Section 309 covers powered industrial trucks, including their battery chargers, ventilation and no-smoking signs. Large banks of batteries used for energy storage are a separate chapter and a separate permit, not a charging station. Where the station is new or the shop is adding circuits, the fire marshal's preference about detection and location is worth asking before the work rather than after the inspection.

A worked example: one wall, fourteen packs and a walkie

A twelve-person electrical and low-voltage shop charges fourteen tool packs on twelve chargers and has one walkie stacker with a flooded lead-acid battery. Before the change, the chargers sat on a plywood bench by the back door, plugged into two six-outlet power strips plugged into each other on one 20 A circuit. Boxes of fittings were stacked against the bench. The walkie charged in the corner under a low ceiling with no exhaust.

The electrical load. Each charger's nameplate reads 1.8 A input at 120 V (read your own; these vary by model). Twelve chargers: 12 x 1.8 = 21.6 A. Treated as a continuous load, which overnight charging arguably is, a 20 A breaker should carry no more than 80 percent of its rating, 16 A, under NEC 210.20 as adopted by your jurisdiction. Eight chargers would be 8 x 1.8 = 14.4 A and fit; nine would be 16.2 A and not. Twelve need two circuits. The electrician the shop called in split them six and six, 6 x 1.8 = 10.8 A per circuit, with a receptacle for each charger, and the daisy-chained power strips went in the trash. Relocatable power taps are listed for use plugged directly into a receptacle, not into each other.

The surface and clearance. A steel shelf replaced the plywood bench, on the back wall away from the door. The fitting boxes moved to the rack aisle, 9 feet away, well past the 3-foot default.

Detection. The building had a monitored alarm with no device in the back corner. The alarm contractor added a heat detector over the shelf because forklift exhaust and dust had produced nuisance trips on smoke detectors elsewhere in the shop.

The walkie. The lead-acid charger moved to the same wall, mounted on it, on its own circuit sized from its nameplate, under a new exhaust fan high on the exterior wall. A pair of bollards went in front of the charger. A plumbed eyewash went 10 feet away at the utility sink, with neutralizer on a shelf beside it.

Damaged packs. A lidded steel can with sand, labeled DAMAGED PACKS - DO NOT CHARGE. On the first day, two packs went in it: one with a cracked case and one that would not seat in its tool.

What would have changed it. If the walkie had a sealed or lithium battery, the exhaust fan and eyewash would have been driven by the maker's manual rather than by the gassing and acid hazards of a flooded battery, though 1910.178(g)'s designated area still applies to a powered industrial truck. If the shop had no monitored alarm at all, the detection decision would have moved up the list, because a standalone alarm sounding in an empty building at night alerts nobody.

What failure looks like

Packs charging on the seat of a truck because the shelf is full. A pack in the quarantine bin that someone fished out because it "seemed fine." A charger with a cracked cord. The eyewash bottle out of date or the plumbed unit not flushed in months. The exhaust fan switched off because it was loud. The monthly safety walk is where each of these gets seen.

References

• 29 CFR 1910.178(g), changing and charging storage batteries, and 29 CFR 1910.151(c), eye and body flushing, OSHA general industry
• ANSI/ISEA Z358.1, emergency eyewash and shower equipment
• International Fire Code, Section 309 (powered industrial trucks), 2021 edition, and NEC 210.20, as adopted by your jurisdiction
• See related: Lithium-Ion Batteries in Tools, Vans and Customer Equipment