8. BATTERY SAFETY

8.1 EXPLOSIVE HAZARD

All storage batteries give off a highly explosive mixture of hydrogen and oxygen when gassing. TThheerreeffoorree,,  nneevveerr  ppeerrmmiitt  ssppaarrkkss,,  ooppeenn  ffllaammee,,  oorr  lliigghhtteedd cigarettes near a storage battery.cigarettes near a storage battery. Post "No Smoking" signs where they are clearly visible to anyone entering the battery room area. A nonmetallic flashlight is desirable for battery inspection. Use only alcohol thermometers when taking electrolyte temperatures. Keep all battery connections tight to avoid sparking. Never lay any metallic object on top of a battery. A class C 10­ pound fire extinguisher should be mounted just inside the battery room door. Carbon dioxide (CO2) is not recommended because of the potential for thermal shock to the batteries.

8.2 ELECTROLYTE HAZARD

When handling electrolyte, wear face shields (face shields should not have metal reinforcing rims, which could cause a battery short if dropped), rubber aprons, and rubber gloves; avoid splashes. The electrolyte is injurious to skin and clothing and must therefore always be handled carefully. The eyes in particular should be guarded. If acid is splashed into the eyes or anywhere on the skin, flood with water for at least 15 minutes and get medical attention. Do not use bicarbonate of soda on the skin, which may aggravate the burn. For neutralization of acid electrolyte spilled on the floor or rack, a bicarbonate of soda solution—1 pound per gallon of water—is recommended.

For neutralization of ni-cad battery electrolyte (potassium hydroxide), keep a concentrated solution of 20 ounces of boric acid powder per gallon of water available for neutralizing spills on skin or clothing. Use plain water to wash up spills of potassium hydroxide on the cells or racks. Care must be taken to prevent the solution from getting into the cells.

A combination eye-wash, face, and body spray unit must be located within 25 feet of each battery room or battery system. These units can be permanently mounted and connected to the facility's potable water system

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or can be of a portable pressurized type.

8.3 FLAME ARRESTERS PURPOSE AND CLEANING

Article 480-9 of the National Electric Code requires each vented battery cell to be equipped with a flame arrester designed to prevent destruction of the cell attributable to an ignition of gases outside the cell.

The diffuser material of flame arresters can become partially clogged from electrolyte spray if cells are overfilled with water or have been excessively overcharged. Flame arresters should therefore be inspected annually, and all arresters having clogged pores should be replaced or cleaned as follows:

1. Immerse the flame arrester several times in fresh water in a plastic bucket.

2. Eject the water after each immersion by vigorous shaking or an air blast.

3. Dump and refill the bucket with clean water for every 15 flame arresters that are cleaned.

4. Do not use any cleaning or neutralizing agents in the water because any dry residue may clog the pores of the diffuser materials.

8.4 VENTILATION

A determination must be made for each battery area as to whether sufficient ventilation is being provided to ensure adequate diffusion of hydrogen gas during maximum gas generating conditions. Such determination can be made from the following data:

1. When the battery is fully charged, each charging ampere supplied to the cell produces about 0.016 cubic feet of hydrogen per hour from each cell. This rate of production applies at sea level, when the ambient temperature is about 77 EF, and when the electrolyte is "gassing or bubbling."

2. Number of battery cells and maximum charging rate (not float rate) can be obtained from specifications or field inspection.

3. Hydrogen gas lower explosive limit is 4 percent by volume. Good practice dictates a safety factor of 5, which reduces the critical concentration to 0.8 percent by volume. This large safety factor is to allow for hydrogen production variations with changes in temperature, battery room elevation, and barometric pressure and also allows for deterioration in ventilation systems.

4. Examples of calculations for determining adequate battery room ventilation appear below:

Example 11

A fully-charged, 60-cell, lead-acid battery, located in a room having a volume of 60 cubic meters, is being charged at 50 amperes. The ventilation system is designed to provide three air changes each hour. Determine the rate of hydrogen production, the critical volume of the battery room, and the adequacy of the air exchanges required for ventilation.

Hydrogen (H2) production in cubic meters per hour is:

(50 amps)(60 cells)(0.000453 m3 H2/cell/hour) = 1.359 m3 H2/hour

Critical volume, with safety factor based on 0.8 percent by volume is:

(0.008)(60 m3) = 0.48 m3 H2

Hours to produce critical level of 0.8 percent hydrogen (0.48 cubic meters) in the 60-cubic-meter battery room is:

0.48 ÷1.359 = 0.35 hour (21 minutes)

The ventilation system must move 60 cubic meters (the room volume), with the 0.48 cubic meters of hydrogen contained within, before the 0.35 hour (21 minutes) elapses.

Three air changes each hour provide one air change in 20 minutes, which is quicker than the 21 minutes required. Critical hydrogen concentration will not be reached with continuous operation of the ventilation system.

Example 22

Same condition as previously mentioned except that the battery is located in a general control room area of 15 by 7 by 5 meters with one air change per hour:

Hydrogen production rate per hour:

(50 amps)(60 cells)(0.000453) = 1.353 m3 H2/hour

Critical volume based on 0.8 percent:

(0.008)(15 m)(7 m)(5 m) = 4.20 m3 H2

Hours to produce critical level of 4.20 cubic meters of hydrogen:

4.20 ÷ 1.353 = 3.10 hours, or 3 hours and 6 minutes

Because one air change occurs per hour, the critical concentration would not be reached with continuous operation of the ventilation system and with adequate air movement over the battery to ensure diffusion of generated gases.

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Same condition as example 2. Determine fan size for room with no natural

circulation.

Hydrogen production in cubic meters per hour:

(0.000453 m3/hour)(50 amps)(60 cells) = 1.35 m3/hour

Because fans are rated in cubic feet per minute, cubic meters per hour must

be converted to cubic feet per minute:

(1.35 m3/hour)(35.31 ft3/m3) = 47.67 ft3/hour H2 production

Divide by 60 minutes per hour to change 47.67 cubic feet per hour into cubic feet per minute.

47.67 ÷ 60 = 0.794 ft3/min H2 production

A safety factor of 5 (0.8 percent by volume) is required. With 0.794 cubic foot per minute hydrogen production, the hydrogen must never reach 0.8 percent of the total volume of the room. Total volume of the room is (15 m)(7 m)(5 m) = 525 m3.

(525 m3)(35.32 ft3/m3) = 18,538 ft3 total volume of the room

0.8 percent of 18,538 ft3 = 148.3 ft3

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So the fan must clear the room before the hydrogen generation can produce 148.3 cubic feet of hydrogen. This production is 0.794 cubic foot per minute, so:

148.3 ft3 ÷ 0.794 ft3/min = 186.7 min to clear the room before H2 volume is produced

The total room volume is 18,538 ft3, so:

18,538 ÷ 186.7 = 99.29-ft3/min fan capacity

Fans are rated in hundreds of cubic feet per minute, so at least a 100-cubic- foot-per-minute fan is needed.

Another way to calculate this fan size would be that the fan must move 0.8 percent of the total volume of the room each minute. So divide the hydrogen production rate by 0.8 percent to give the total fan capacity.

0.794 ft 3 /min ÷ 0.008 = 99.25 ft 3 /min

8.5 BATTERY ROOMS

Battery rooms in future and remodeled facilities are to be designed, constructed, and maintained in accordance with section 14—Storage Batteries—of the National Electrical Safety Code. Battery systems now located in control buildings or powerplants need not be placed in a separate room. However, when not located in a separate room, barriers or some type of mechanical protection must be provided to prevent inadvertent personnel or equipment contact and resultant damage. Periodic air flow measurements and explosion meter (total combustible gas) readings are recommended in the general battery areas to ensure adequate air movement to diffuse generation of hydrogen gas.

“No Smoking,” “No Sparks,” or “No Open Flame” signs should be posted on the outside of the door.

Seismic protection should be provided in areas with high seismic activity.

Metal battery racks shall be grounded.

Concrete floors shall be painted with acid-resistive paint (alkaline resistive) for ni-cad batteries.

Electrical receptacles and light switches should be located outside of battery areas.

A 10-pound class C fire extinguisher should be located just inside the battery room door. The fire extinguisher should not be a CO2 type to prevent thermal shock to the battery. Egress from the battery room must be kept clear at all times.

8.6 SAFETY MEETINGS

Field maintenance and operation personnel shall be informed of design criteria and operational requirements of ventilation system performance. Such information will be posted on battery room doors or in close proximity to battery systems. Discussions of these rules and regulations shall be the subject of at least one toolbox meeting semi-annually. Operation of the fire extinguisher and how to read the inspection tag must be covered