FEATURE HAZARDOUS AREA EQUIPMENT
AVOIDING HYDROGEN EXPLOSIONS WITH BATTERY ROOM VENTILATION
E
veryone knows the function of a battery; to store electricity in the
form of chemical energy and to convert it 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. When mixed with oxygen, hydrogen 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 includes protecting personnel with protective
hour of charging, mechanical ventilation using exhaust fans is recommended. This should be a compulsory requirement even if the concentration is not expected to reach one per cent, due to uncertainties in building geographies, high points or inadequate and blocked openings for natural ventilation. Ventilation should ideally be placed at
work wear. 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 and suggests that hydrogen concentration levels are kept below one per cent to avoid the risk of explosion. The National Fire Protection Association lists the explosive concentration level, or lower explosive level (LEL) of hydrogen as four per cent, so the legislation encourages the safe implementation of ventilation systems to avoid explosions far below the stipulated four per cent explosive level. If the level of hydrogen in a battery room exceeds one per cent after one
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 a solution. If this is 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 the telephone number below.
Axair Fans T: 01782 349 430
www.axair-fans.co.uk
DOUBLE UNDER VOLTAGE MONITORING RELAY FOR HAZARDOUS ENVIRONMENTS
Carlo Gavazzi launches the DUB72 double under voltage relay for Class 1 Division 2 applications according to ANSI/ISA12.12.1 for potentially explosive environments. The user can set two independent dials, one for each of the two thresholds, measuring the level of its power supply. One of the thresholds, the one associated with output 1, can be used as a pre-alarm signal; the other is associated with a high- power 20A-rated relay, which can be used to drive the load directly and features a low-profile DIN housing suitable for installation into electric distribution panels, as well as industrial cabinets. Thanks to the high-powered
electromechanical 20A relay, the second threshold / relay can be used to directly disconnect the battery or load. The two relay outputs can be associated to one of
8 APRIL 2018 | ELECTRICAL ENGINEERING A green/red LED provides a visual
indication of the alarm status. The number of RED blinks indicates the triggered alarm type. The PCB tropicalisation increases operational reliability also in humid and dusty environments. As the DUB72 complies with the
the set thresholds and can be used to drive different types of loads: the 3A can be used to send a signal to a PLC, while thanks to its high capacity the 20A could directly drive the load.
hazardous location installation norm, it is suitable for 24V-battery-voltage level monitoring, or any other DC voltage within the operating range of 16vdc to 26vdc, in any environment including Class 1, Division 2 of potentially explosive environments. It is suitable for applications where it is necessary to monitor the battery charge level in oil and gas installations or agricultural industry.
Carlo Gavazzi
www.carlogavazzi.co.uk
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