nickel-cadmium cells used in the battery consist of two basic types–vented and sealed cells. Most naval aircraft nickel-cadmium storage batteries employ rectangular vented-type cells. Sealed cells have limited applications and come in both the rectangular and cylindrical types. BATTERY SAFETY PRECAUTIONS The principal hazard in working with lead-acid batteries is acid burns when you are refilling or handling them. You can prevent getting burned by wearing eyeshields, rubber gloves, rubber aprons, and rubber boots with nonslip soles. Rubber boots and aprons are only needed when you are refilling batteries. You should wear eyeshields whenever you are working around batteries. Eyeshields will prevent acid burns to your eyes. Wood slat floorboards, in good condition, will help prevent slips and falls. Additionally, electric shock from the high-voltage side of charging equipment is reduced. Another hazard of working with batteries is the chance of an explosion. Hydrogen gas, a high explosive, collects while batteries are charging and can cause an explosion during battery charging. This is especially true when using the accelerated charging method. The charging rate should be held to a point that prevents the rapid release of hydrogen gas. Follow the manufacturers' recommendations for the charging rates. Be careful to prevent short circuits while batteries are being charged, tested, or handled. A spark from a shorted circuit could easily ignite the explosive gases. This danger is also true for personnel performing aircraft maintenance near batteries. Open flames or smoking are not permitted in the battery charging room. Use a shop exhaust system to remove the gases. Use extreme caution when you are installing or removing an aircraft battery. Batteries are heavy for their size and awkward to handle. These characteristics require the use of proper safety precautions. Aircraft batteries may overheat because of internal shorting or thermal runaway. In either case, an overheated battery causes a hazardous condition. When an overheated battery is detected, crash crew personnel should open the battery compartment and check for the following conditions: !    Flame—If present, use CO₂ extinguisher. !    No flame—If smoke, fumes, or electrolyte is coming from the battery or vent tubes, spray the battery with low-velocity water fog. This will lower the battery temperature. WARNING CO₂  is a good fire-extinguishing agent once a fire has started. Never spray CO₂ from a portable fire extinguisher into a battery compartment for cooling or to displace explosive gases. The static electricity generated by the discharge of the extinguisher could explode the gases trapped in the battery compartment. Following a visual check, allow crash crew personnel to remove the battery. If additional battery cooling is required, use low-velocity water fog. You may use the above procedures on all types of aircraft batteries installed in all types of aircraft. CAUTION If acid or electrolyte from a lead-acid battery touches your skin or eyes, flush the affected area with  large  quantities  of  fresh  water.  Report immediately for medical examination and treatment. CAUTION If  the  electrolyte  from  a  nickel-cadmium (NICAD) battery touches your skin or eyes, flush the affected area thoroughly with large quantities of fresh water. Neutralize with vinegar or a weak solution (3%) of boric acid. Report immediately for medical examination and treatment. Q7-1. What  are  the  two  primary  sources  of electrical energy for an aircraft? Q7-2. During  normal  aircraft  operation,  what component maintains the battery in a charged state? Q7-3. What are the principal hazards of working with batteries? Q7-4. What can cause aircraft batteries to overheat? Q7-5. What should you do if acid or electrolyte from a lead acid battery comes in contact with your skin? Q7-6. What are the two ways to neutralize electrolyte from a nickel-cadmium (NICAD) battery if it contacts your skin? 7-2