switchgear line-ups are 125 V or 250 V nominal systems, and feature redundant battery chargers with independent power sources. Separate battery rooms may be provided to protect against loss of the station due to a fire in a battery bank. For stations that are capable of black start, power from the battery system may be required for many purposes including switchgear operations. Very large utility batteries may be used for grid energy storage. Submarines and ocean-going vessels Battery rooms are found on diesel-electric submarines, where they contain the lead-acid batteries used for undersea propulsion of the vessel. Even nuclear submarines contain large battery rooms as backups to provide maneuvering power if the nuclear reactor is shut down. Batteries in surface vessels may also be contained in a battery room. Battery rooms on ocean-going vessels must prevent seawater from contacting battery acid, as this could produce toxic chlorine gas. This is of particular concern on submarines. Design issues Since several types of secondary batteries give off hydrogen if overcharged, ventilation of a battery room is critical to maintain the concentration below the lower explosive limit. The number of air changes per hour required to prevent unsafe accumulation can be calculated from the number of cells and the charging current, given the chemistry of the battery. The life span of secondary batteries is reduced at high temperature and the energy storage capacity is reduced at low temperature, so a battery room must have heating or cooling to maintain the proper temperature. Batteries may contain large quantities of corrosive electrolytes such as sulfuric acid used in lead-acid batteries or caustic potash (aka potassium hydroxide) used in NiCad batteries. Materials of the battery room must resist corrosion and contain any accidental spills. Plant personnel must be protected from spilled electrolyte. In some jurisdictions, large battery systems may contain reportable amounts of sulfuric acid, a concern for fire departments. Battery rooms in industrial and utility installations typically have an eye-wash station or decontamination showers nearby, so that workers who are accidentally splashed with electrolyte can immediately wash it away from the eyes and skin. See also List of battery types Battery storage power station References Further reading Kusko, Alexander (1989). Emergency/Standby Power Systems, pp. 99–117. New York: McGraw-Hill Book Co., . National Fire Protection Association (2005). 'NFPA 111: Standard on Stored Electrical Energy Emergency and Standby Power' Battery (electricity) Electric power Rooms Telecommunications infrastructure