Storage batteries are considered a live source and appropriate precautions should be taken when working around them. Information regarding batteries and battery rooms can be found in OSHA, NESC, NFPA 70E Article 240 and 320, NEC 480.
7.5.1 Surrounding Space
Adequate space should be provided around storage batteries for safe inspection, maintenance, testing, and cell replacement. Space shall7.36 be left above cells to allow for operation of lifting equipment when required, for addition of water, and for taking measurements.
7.5.2 Location
Storage batteries should be located in a protective enclosure or area accessible only to qualified persons. A protective enclosure can be: a battery room; a control building; or a case, cage, or fence that shall7.37 protect the contained equipment and minimize the possibility of inadvertent contact with energized parts.
7.5.3 Ventilation
The battery storage area shall7.38 be ventilated by either a natural or powered ventilation system to prevent accumulation of hydrogen. The ventilation system shall7.38 limit hydrogen accumulation to less than an explosive level.
7.5.4 Conduit
Because the vapors given off by a storage battery are very corrosive, the wiring should withstand the corrosive action, and special precautions are necessary as to the type of insulation used and the protection of all metalwork. It is stated by their respective manufacturers that a conduit made of aluminum or silicon-bronze is well-suited to withstand the corrosive effects of the vapors in battery rooms. In contrast, if steel conduit is used, it is recommended that it be zinc-coated and kept well-painted with asphaltum paint.
7.5.5 Battery Room
There are no special requirements for the type of fixtures or other electrical equipment used in the battery room, with proper ventilation. (See NEC 480 and Fig. 7-5.)
Fig. 7-5. Wiring and equipment installed in battery rooms.
7.5.6 Personal Protective Equipment
Those working on or servicing batteries shall7.39 use PPE capable of protecting employees from acid splashes. The minimum acceptable PPE shall7.40 include acid-resistant gloves, aprons, and chemical-splash goggles. A full-face shield may also be used; however, it should not be worn in place of goggles. When conditions necessitate, PPE should be AR. The use of PPE for wear when servicing batteries shall7.41 comply with OSHA requirements. Safety showers and eyewash stations are also required.
7.5.7 Tools
Tools used for working on batteries shall7.42 be insulated or non-sparking.
7.5.8 Storage Batteries and Battery Banks
The following subsection covers rechargeable batteries used as a source of electrical energy.
This category is not limited to batteries of a particular voltage and energy rating, since the nature of the associated electrical hazards is similar without regard to battery size. The severity of the hazard increases as the battery ratings increase.
7.5.8.1 Types of Hazards
Some of the types of hazards associated with storage batteries and battery banks are as follows:
1. Accidental grounding of one polarity of a battery bank can create a hazardous voltage between the ungrounded polarity and ground.
2. Accidental shorting of the exposed terminals or cables of a battery can result in severe electric arcing (DC arc flash), causing burns and electric shock to nearby personnel.
3. Hydrogen gas generated during battery charging can create fire, explosion, and toxicity hazards.
4. Exposed terminals in a battery bank present electric shock hazards.
5. Batteries, particularly sealed-cell batteries, can explode if they are shorted, or if they are charged at excessively high rates.
6. Electrolytes can be highly corrosive and can produce severe burns to personnel on contact.
7.5.8.2 Design and Construction Criteria
Reliable design and construction criteria for storage areas for batteries are as follows:
1. Battery installations should conform to the requirements in the current edition of the NEC and the NESC.
2. Battery banks should not be grounded, except as required in the NEC. A ground detector should be used to indicate an accidental ground.
3. Batteries should be mounted to allow safe and convenient access for maintenance.
4. Lockable doors should be provided to control access to rooms or enclosures containing battery banks.
5. Approved safety showers and eyewash stations should be provided close to battery banks.
6. Appropriate ventilation for discharges of gas should be provided.
7. In areas where seismic activity is present, the installation should be designed according to local standards.
7.5.8.3 Operating Criteria Operating criteria are as follows:
1. Maintain battery bank connections that are clean and tight to prevent excessive heating because of contact resistance.
2. Do not repair battery connections when current is flowing. An accidental opening of the circuit could result in a hazardous arcing condition.
3. Clearly post electrical and other hazards of battery banks and emergency first aid information near the equipment.
4. Arrange the battery banks so that temperature stratification does not result in over- or under-charging.
Note: The optimum storage temperature for maximum battery life for lead-acid batteries is 77°F
± 2° (25°C ± 1).
7.5.8.4 VRLA Battery (valve-regulated lead–acid battery)
A VLRA battery, more commonly known as a sealed battery is a lead–acid rechargeable battery. Because of their construction, VRLA batteries do not require regular addition of water to the cells, and vent less gas than flooded lead-acid batteries. The reduced venting is an advantage since they can be used in confined or poorly ventilated spaces. But sealing cells and preventing access to the electrolyte also has several considerable disadvantages as discussed below. VRLA batteries are commonly further classified as:
Absorbed glass mat (AGM) battery
Gel battery ("gel cell")
An absorbed glass mat battery has the electrolyte absorbed in a fiber-glass mat separator. A gel cell has the electrolyte mixed with silica dust to form an immobilized gel.
While these batteries are often colloquially called sealed lead–acid batteries, they always include a safety pressure relief valve. As opposed to vented (also called flooded) batteries, a VRLA cannot spill its electrolyte if it is inverted. Because AGM VRLA batteries use much less electrolyte (battery acid) than traditional lead–acid batteries, they are sometimes called an "acid- starved" design.
The name "valve regulated" does not wholly describe the technology. These are really
"recombinant" batteries, which means that the oxygen evolved at the positive plates will largely recombine with the hydrogen ready to evolve on the negative plates, creating water and preventing water loss. The valve is a safety feature in case the rate of hydrogen evolution becomes dangerously high. In flooded cells, the gases escape before they can recombine, making it necessary to add water periodically.
VRLA batteries offer several advantages compared with flooded lead–acid cells. The battery can be mounted in any position, since the valves only operate on overpressure faults. Since the battery system is designed to be recombinant and eliminate the emission of gases on
overcharge, room ventilation requirements are reduced and no acid fume is emitted during normal operation. The volume of free electrolyte that could be released on damage to the case or venting is very small. There is no need (nor possibility) to check the level of electrolyte or to top up water lost due to electrolysis, reducing inspection and maintenance.
Because of calcium added to its plates to reduce water loss, a sealed battery recharges much more slowly than a flooded lead acid battery. Compared to flooded batteries, VRLA batteries are more sensitive to high temperature, and are more vulnerable to thermal run-away during abusive charging. The electrolyte cannot be tested by hydrometer to diagnose improper charging, which can reduce battery life.