Wednesday, November 18, 2015
A fire and explosion can end up with devastating consequences, resulting in serious injuries or death of employees and others, as well as considerable damage to property. A person conducting a business or undertaking work must prevent the possibility of fire or explosion from an ignition of flammable substances associated with a hazardous area or a hazardous atmosphere.
A hazardous area is defined as an area which an explosive atmosphere is present, or maybe expected to be present.
The international standards outline three levels of Hazardous Area Classifications: Zone 0, Zone 1 and Zone 2.
- Zone 0: An area in which an explosive atmosphere is present continuously, or is present for long periods.
- Zone 1: An area in which an explosive atmosphere is likely to occur periodically in normal operation.
- Zone 2: An area in which an explosive atmosphere is not likely to occur in normal operation and if it does occur it will only exist for a short period. Types of Protection for Gas / Vapour
Zone 0, 1 and 2
- Ex ia – Intrinsically safe.
- Ex ma – Encapsulation.
Zone 1 and 2
- Ex d – Flameproof
- Ex ib – Intrinsically Safe
- Ex p – Pressurised Enclosure
- Ex pl – Purged Enclosure
- Ex px - Purge / pressurised
- Ex py – Purge/ pressurised
- Ex mb – Encapsulation
- Ex e – Increased Safety
- Ex s – Special
- Ex m - Encapsulation
- Ex o – Oil Immersion
- Ex q – Powder / sand filled
- Ex n – Non Sparking
- Ex pz – Purge / pressurised
- Ex ic – Intrinsic Safety
- Group l – Coal Mining (methane)
- Group ll – Other Industries
- Group llA (e.g. propane , butane)
- Group llB (e.g. ethylene , butadiene)
- Group llC (e.g. acetylene , hydrogen)
The maximum service temperature of the equipment should not exceed the ignition temperature of the gas or vapour based on an ambient 40°C.
- T1 - 450 °C
- T2 - 300°C
- T3 - 200°C
- T4 - 135°C
- T5 – 100°C
- T6 - 85°C
Risk Control Measures
Key control measures for managing these risks include:
- identifying and managing hazardous areas
- controlling emissions of flammable vapours, gases and mists (see below)
- use of ventilation systems to control vapours during both normal and abnormal conditions (e.g. leak or spill)
- eliminating ignition sources from hazardous areas (see below)
- installing systems to detect leaks of flammable gases or vapours and enable response actions to be taken
- using intrinsically safe or flameproof equipment
- substituting flammable materials for ones that are less flammable or combustible
- ensuring incompatible materials (e.g. oxidizers and oils) are separated or segregated
- reducing quantities of flammable and combustible materials, including items that contribute to the fire load but that are not hazardous chemicals themselves (e.g. wooden pallets, oil)
- ensuring equipment used in handling flammable hazardous chemicals is maintained in accordance with manufacturer's instructions
- adopting good housekeeping practices to minimise accumulation of combustible dusts.