Everyone knows the function of a battery, to store electricity in the form of chemical energy and to convert to electrical energy when required. Vented lead acid batteries or flooded batteries as they are also commonly known, consist of plates that are flooded in an acid electrolyte. When charging, the electrolyte emits hydrogen through the vents in the battery. Under normal operations, the release of hydrogen is relatively small, but this is elevated during heavy recharge periods.
Hydrogen when mixed with oxygen, is a highly explosive substance that is odourless, colourless and lighter than air. The lightweight element accumulates above the oxygen, and where effective ventilation is not in place, a build-up can occur. In extreme circumstances there have been cases of battery room explosions as a result of ineffective battery room ventilation. A small smoulder can create a huge explosion when hydrogen is in the presence of oxygen, and besides this, hydrogen is hazardous to health, causing skin burns and eye issues.
Dismissing a critical safety issue is clearly not responsible, system integrators in commercial, industrial and dockyard applications need to identify the risks and design a system to protect in a fail-safe way. This also includes protecting personal with protective workwear. The likelihood of an explosion occurring depends on the number of batteries, the charge rate, the size of the room and the ventilation available. Legislation advises the number of air changes per hour, for example IS:1332 Battery Rooms advises 12 air changes per hour, or suggest that hydrogen concentration levels are kept below 1% to avoid the risk of explosion.
The National Fire Protection Association lists the explosive concentration level, or Lower Explosive Level (LEL) of hydrogen as 4%, so the legislation stipulating a maximum level below 1% encourages the safe implementation of ventilation systems to avoid explosions far below the stipulated 4% explosive level.
If the level of hydrogen in a battery room exceed 1% after one hour of charging, mechanical ventilation using exhaust fans is recommended. This should also be a compulsory requirement even if the concentration is not expected to reach 1%, due to uncertainties in building geographies, high points or inadequate and blocked openings for natural ventilation.
Ventilation should ideally be placed at both high points (for the exhaust of hydrogen that accumulates above the oxygen), and low points within the battery room to encourage forced ventilation out of the room. There should be no air recirculation under any circumstances as this encourages the mix of the two gases, and where possible, on a separate ventilation system than the rest of the building. Corrosion resistant fans with ATEX non sparking components, ideally roof mounted to exhaust upward and out are the ideal solution, but if not possible, ATEX wall mounted axial fans with back draught dampers, to avoid the return of hazardous substances, can be used.
For more information, or to discuss the use of industrial fans for battery room ventilation, or any other air movement application, contact Axair Fans on: 01782 349 430