According to a study from the National Highway Traffic Safety Administration (NHTSA), in 1993 an estimated 7,051 persons were treated in hospital emergency rooms for injuries resulting from a motor vehicle battery. The injuries were caused by several things, including battery explosions, battery acid, and electrical shock. That statistic only includes the injuries that occurred from motor vehicle batteries. It does not include the unknown number of injuries resulting from batteries in forklifts, golf carts, power storage battery arrays, and other battery powered equipment. The largest number of injuries occurred as a result of a battery explosion. The total number of battery explosions is unknown. In some cases the injuries were not reported, and other explosions occurred where no injuries resulted.
The example in the picture below shows a battery that exploded while it was being charged. This article discusses the hazards associated with vented lead-acid batteries, and the precautions that should be taken to help prevent injuries.
- Personal Protection
While performing battery maintenance or any other task in close proximity to a battery, protective clothing, eye and face protection, and rubber gloves must be worn to help prevent injury that may be caused by battery acid, electrical shock, or a battery explosion. The goggles must be impact resistant and have fully enclosed side guards. To protect your face, an impact resistant transparent shield that covers your entire face is recommended. Batteries can pose a risk of electrical shock and serious burns caused by electrical arcing. This is especially true of series connected batteries. Rubber gloves must be worn to minimize the risk, and to prevent lead exposure resulting from skin contact with the battery terminals or intercell connectors. Consult and follow the precautions listed on the battery manufacturers’ data safety sheet.
All vented lead-acid batteries produce both hydrogen and oxygen gas. This gas mixture is extremely flammable and will likely explode if ignited. If the flame enters the battery itself, the gases trapped inside will ignite causing the battery to violently explode, propelling shrapnel and acid in every direction. Therefore appropriate precautions must be taken to avoid injury. Always work in a well ventilated area to disperse the gases away from the battery to help prevent the accumulation of an explosive mixture. Lead-acid batteries emit an acid mist which is harmful if inhaled. Precautions must be taken to avoid breathing the fumes. The vent caps must remain tightly sealed while the battery is charging to avoid electrolyte spray, to reduce toxic fumes, and to reduce the risk of an explosion.
- Short Circuit Prevention
Check to make sure that all battery terminals covers are in place, and that no metallic portion of the terminals is exposed. If any covers are damaged or missing, they should be replaced. The terminal covers should only be removed when connecting or disconnecting the battery cables, and should be replaced immediately thereafter. Where multiple batteries are connected together in series, ensure that all intercell connectors are covered with a non-conductive shroud. To prevent injury caused by an electrical short circuit, all metallic items including jewelry, watches, rings, etc. should be removed prior to working on a battery. Use only non-conductive or insulated tools. Never lay metallic tools or any other conductive items on top of a battery.
- Battery Charging
Before recharging a battery, visually check the electrolyte level to ensure that all battery plates are covered with electrolyte. If they are not, add only enough distilled water to cover any exposed plates. The battery should only be completely filled after it has been recharged. The electrolyte level is affected by the state of charge, and the level is highest after the battery is fully charged. Adding water before charging may result in an overfilled battery, or in acid overflowing out of the battery. Make sure the charger is turned off and unplugged before connecting or disconnecting it to the battery to prevent arcing. Read and follow all instructions in the charger manual.After the battery is fully recharged, check the electrolyte level and add water if needed. For most batteries, the correct electrolyte level is approximately ¼ to 1/8 of an inch below the bottom of the vent well. Only use distilled water. Never add sulfuric acid to a battery. During normal operation, a battery loses only water, not sulfuric acid.
The chances of an explosion are much greater while a battery is being charged, since hydrogen gas is produced at a higher rate during the charging process, thus a greater amount of caution must be used. Do not perform maintenance on a battery while it is being charged. Wait until after the charging cycle is complete, and then allow additional time for the gases and fumes to dissipate before going near the battery. If the battery is contained in a covered enclosure, remove the cover while the battery is charging to prevent the accumulation of explosive gases, and do not replace the cover until after the charging cycle is complete.
- Fire & Explosion Prevention
Smoking, open flames, sparks, electrical arcing, brush type electric motors, and all other possible ignition sources must be avoided and kept far away from batteries to prevent the ignition of flammable gases. All electrical loads on the battery must be discontinued prior to performing battery maintenance. Battery connections must be performed in the proper sequence to prevent arcing. Always disconnect the negative (black) terminal connector before connecting or removing the positive (red) terminal connector.To reduce the risk of a battery explosion, all battery vent caps should contain a flame arrestor (also called a spark arrestor), but some are manufactured without one. A flame arrestor stops a flame from entering the battery where it can ignite the internal gases, causing the battery to explode. Per the National Electrical Code, flame arrestors are required for all stationary installations of storage batteries. To comply with this regulation, each battery vent cap must contain a flame arrestor. If yours do not, replacement safety vent caps are available.
For safety instructions on how to jump start a car battery, click here to view the free guide provided by the Texas Department of Insurance.
OSHA regulations: 1917.157, 1926.441 (https://www.osha.gov )
2017 National Electrical Code, Article 480.11 (A)
NHTSA publication #97840 (https://www.nhtsa.gov)