There appears a level of consternation swirling about of late that is rooted in varying interpretations by Authorities Having Jurisdiction (AHJ) such as building inspectors, electrical inspectors and so on regarding international building codes now that they have been adopted over national codes in many US jurisdictions. The intention of this paper is to identify the international codes covering hydrogen evolution in stationary battery strings and compare them with national codes, IEEE practices, Telephone company best practices and practical experience. Conclusions to be drawn will identify perhaps a need for soundly reasoned input to the next international code cycle and a reiteration of best practices for stationary battery installations.
First and foremost, the telecommunications and data center industries have an excellent reputation for safety and that includes its handling of hydrogen evolved from battery cells. In more than a century of operation of greater than a hundred thousand battery installations nationally, one could count on his or her fingers the number of hydrogen related explosions that caused damage to a facility and none of those resulted in injury. Even battery jar explosions are quite rare.
In part, many of the issues at hand are related to the wide deployment of Valve Regulated lead Acid batteries (VRLA) because these cells typically outgas only about 5% of hydrogen volumes as their vented (AKA flooded) counterparts. As written, however, the codes specify that ventilation must limit hydrogen accumulations that might result during worst case conditions, typically an overcharge condition or thermal runaway state when little or no gas recombination is occurring. This requirement causes grief in some instances because in the case of continuous ventilation it flies in the face of energy conservation. To provide ventilation for the worst case battery condition is effective only in unconditioned spaces. However, if the area being ventilated is conditioned space, potentially large volumes of expensively cooled air are being pushed outdoors, thus raising the cooling cost and the carbon footprint for the facility.
An exaggerated model of the problem is seen in the shops and stores in Disney World where customer sales floors are heavily air conditioned but the doors are either wide open or there are no doors at all. The scheme works well for tourist impulse buying but from an energy viewpoint it's wasteful. Another approach is the use of an exhaust fan or purge ventilation, under the control of hydrogen sensors; but experience has shown that most such installations are problematic due to wide variance in sensor product quality, miscalibration or delayed calibration and prolific installation errors. Nothing in the fire codes, nor IEEE 450 and IEEE 1187, the industry standard for Vented (also called 'flooded') cells and Valve Regulated Lead Acid, (VRLA) cells require hydrogen detectors, however many AHJs insist upon them. As a practical matter, natural 'pockets' often form in crowded ceiling spaces and hydrogen will rise towards and accumulate in those pockets. The stratification principle is the same whether the space is in a telecommunications facility accumulating hydrogen or a coal mine accumulating pockets of methane. About the only difference is that in a coal mine, a serious explosion generally is a result of two or more sequential explosions. Usually the first explosion is a pocket of methane and a collateral effect of that event is to push a blast wave through the mine shafts blowing up billowing clouds of coal dust which in turn becomes a secondary, usually more powerful explosion or series of them. In either case, whether the side is coming off a cabinet, the roof is coming off a battery room or a mine shaft is blowing apart, the triggering event was an ignition source finding a pocket of gas that had reached its lower explosive limit. Accordingly, the overall site design must address sufficient airflow to prevent the formation of stratification pockets of hydrogen.
Until recently, three model building codes were adopted across the US as is shown on Map 1. The Uniform Building Code (UBC) was adopted over most of the western US, the National Building Code (NBC) covered the northeast and the Standard Building Code (SBC) covered the southeast. In some jurisdictions, a mix and match of codes were adopted by local AHJs within the state.