Flameproof equipment

There is a maximum safe gap measured experimentally which will prevent the transmission of an explosion occurring within a container to a flammable mixture outside the container. Critical and maximum experimental safe gaps for a number of materials in air are listed in Lees (1980, pp. 491-492). These quenching effects are important in the design of flame arresters and flameproof equipment. 

Why were there so many faults Before this inspection, there had been no regular inspections. Many electricians did not understand why flameproof equipment was used and what would happen if it was badly maintained. Spare screws and screwdrivers of the special types used were not in stock, so there was no way of replacing those lost. 

Regular inspections were set up. Electricians were trained in the reasons why flameproof equipment is used, and spares were stocked. In addition, it was found that in many cases flameproof equipment was not really necessary. Division (Zone) 2 equipment—cheaper to buy and easier to maintain—could be used instead. 

As a general rule, the use of organic solvents in chromatographic processes should be minimized, because of the requirement for specialized flameproof equipment which can be extremely costly compared with the equivalent item for a safe area. Where unavoidable, a separate flameproof room for handling solvent-based materials is recommended, with the appropriate specification for mechanical and electrical equipment, controls and room fittings including lights, switches, and telephone systems. 

Flameproof equipment is regarded as safe for use when exposed to the risk of explosive atmosphere for which certification has been given. Electrical apparatus, defined as flameproof, has an enclosure that will withstand an internal explosion of the flammable vapour or gas in question which may enter the enclosure. The joints of the enclosure which are designed with clearance gaps to prevent a build-up of internal pressure also prevent any internal explosion igniting vapour or gas surrounding the equipment. The surface temperature of the enclosure must be below the ignition temperature of the vapour or gas in question, hence the importance of the temperature classification referred to above. Flameproof enclosures are primarily intended for use in Zone 1 or Zone 2 classification but not in Zone 0. 

Other petrochemicals, especially terephthalic acid and PTA, and nylon, as well as polyethylene and polypropylene, require flameproof equipment, and use the vertical decanter, which can be pressurised, and will operate at higher temperatures. These also have polished flights, and chamfered flight tips, without hard surfacing. 

Cable tray routes as per drawing Cable tray suppoits adequate and secure Cable tray assembled and secured correctly Cable ttay earthing as per specification Cable tray earth continuity checks satisfactory Earth cables/bonds securely terminated Cables securely banded/shrouded Correct cable glands fitted Junction boxes and covers securely fitted Flameproof equipment fitted as per specification Lighting fittings correctly erected and secure Distribution boards installed and connected as per drawings... 

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