Batteries are used in a wide variety of vehicle and stationary applications. Large industrial facilities (e.g., warehouses) have designated battery charging areas, most of which require adequate ventilation to exhaust the hydrogen gas that is released during charging. The facility size and the number of chargers in operation simultaneously determine whether natural-draft ventilation is adequate or if forced-draft ventilation is required. During charging, most batteries will offgas hydrogen, making adequate ventilation and the elimination of ignition sources critical attributes of the charging area. That said, it should be noted that certain types of batteries, including lithium ion and lithium metal polymer, do not require ventilation. Manufacturer's data should be consulted to determine appropriate ventilation requirements for the batteries being used.
The Lessons Learned database contains six safety event records (one near-miss and five actual incidents) that deal with the adequacy of ventilation in battery charging areas. Described below, these events occurred in a variety of settings (government facilities, military bases, and private-sector firms), but the need for adequate ventilation was an important lesson learned for all of them.
Description: Hydrogen concentrations rose in an unmanned room containing backup lead-acid batteries after the exhaust fans failed to start at the 1% hydrogen trigger level (i.e., 25% of the lower flammability limit [LFL]). When the concentration reached 2% (50% of the LFL), it triggered a hydrogen alarm that was monitored by a remote network operations center.
Lessons Learned: Redundant safety systems prevented this near-miss from becoming an incident. Following the event, a pressure switch was added to alarm in the event of a fan failure. This alarm is continuously monitored by the network operations center. In the future, the facility will have two ventilation fans: one running continuously and one that is activated if the hydrogen concentration reaches 1%.
Description: A hydrogen explosion occurred in a battery room at a former computer data center. The company had vacated the building and removed all the computer equipment, but left the back-up battery system behind. Ventilation for the battery room was tied into a hydrogen monitoring system. First responders could not tell if the ventilation system had failed or if it had been turned off when the facility was vacated. It appeared that the batteries had been charging for a long time with no ventilation.
Lessons Learned: When facilities/equipment are decommissioned or abandoned, care should be taken to ensure that everything is left in a safe configuration. The battery system was no longer needed, and it should have been decommissioned when the data center was removed. A good management-of-change procedure would have caught this oversight before it caused an incident.
Description: The exhaust fan for a forklift battery charging facility failed, allowing hydrogen gas to build up. A mechanical failure in the fan caused the automatic on/off sensor to overheat and shut off the fan. The facility hazard assessment did not identify the potential hazard of hydrogen buildup due to an exhaust fan failure.
Lessons Learned: The simplicity of this situation illustrates that careful consideration should be given to all aspects of the workplace when trying to identify potential hazards. Some hazardous situations appear so trivial that they can be easily overlooked and serious consequences not understood. Also, some hazardous situations are not readily recognized by nonprofessionals, so professionals from other organizations should be invited to assist with periodic safety assessments and reviews.
Description: A fire occurred in a battery charging room that did not contain any hydrogen detection equipment at a battery manufacturing facility that was about to cease operations for the night. The sprinkler system in this room had been disconnected 10–15 years before the incident due to repeated non-fire activations of the sprinklers. An estimated 5,000 batteries were being charged at the time of the fire.
Lessons Learned: Although a functional fire protection system would have helped to extinguish the fire, a properly designed ventilation system would have prevented the incident altogether. Hydrogen rises twice as fast as helium, at a speed of 45 mph. Therefore, unless a roof or some other structure contains the rising gas, the laws of physics prevent hydrogen from lingering near its point of production. It is unclear whether the room's ventilation system wasn't functioning properly or if it wasn't designed properly. Regardless, those responsible for safety at battery charging facilities need to consult experienced engineering firms on proper location and design of exhaust systems, and standard operating procedures should mandate periodic functional/operational tests of the ventilation systems.
Description: A hydrogen explosion occurred in an emergency battery container that held five batteries. The hydrogen concentration in the container had increased beyond the LFL because the battery charger had inadvertently been left on and the container was placed in an unventilated airlock.
Lessons Learned: During charging, when a battery is almost fully charged, hydrogen and oxygen offgases are released in a flammable mixture. Emergency battery containers must have adequate ventilation for all operations.
Description: During maintenance of an automatic battery charging system, six nickel cadmium batteries that were being reinstalled exploded. Inadequate ventilation of the area appeared to be the main cause of the incident.
Lessons Learned: In facilities housing battery charging systems, it is important to ensure that the ventilation systems are operational and delivering enough outdoor air to properly ventilate the enclosure. Technicians need to be aware of safe practices and proper battery charging protocols for the batteries and charging systems they maintain.