111.15-10—Ventilation.
(a) General.
Each room, locker, and box for storage batteries must be arranged or ventilated to prevent accumulation of flammable gas.
(4)
The power ventilation system must be interlocked with the battery charger so that the battery cannot be charged without ventilation.
(c) Large battery installations.
Each battery room for large battery installations must have a power exhaust ventilation system and have openings for intake air near the floor that allow the passage of the quantity of air that must be expelled. The quantity of the air expelled must be at least:
q=3.89(i)(n).
where: q=quantity of expelled air in cubic feet per hour.
i=Maximum charging current during gas formation, or one-fourth of the maximum obtainable charging current of the charging facility, whichever is greater.
n=Number of cells.
(d) Moderate and small battery installations.
Each battery room or battery locker for moderate or small battery installations must have louvers near the bottom of the room or locker for air, and must be ventilated by:
(ii)
That extends from the top of the room or locker to at least 3 ft. (1 m) above the top of the room or locker;
(iv)
That has no appliances, such as flame arresters, that impede free passage of air or gas mixtures; or
(e) Deck boxes.
Except for a deck box for a small battery installation, each deck box must have a duct from the top of the box to at least 4 ft. (1.2 m) above the box ending in a gooseneck or mushroom head that prevents entrance of water. Holes for air must be on at least two parallel sides of each box.
(g) Boxes for small battery installations.
Each box for a small battery installation must have openings near the top to allow escape of gas. If the installation is in a non-environmentally-controlled location, the installation must prevent the ingress of water.