North American Hazardous Area Protection
Dust-ignition proof, explosion proof, instrinsically safe and nonincendive protection of hazardous areas
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Explosions of volatile liquids and gases resulting in severe fire conflagrations are real hazards, involving high economic costs and often, injury or loss of life.
The types of protection required for electrical components in the areas depends on the risks involved. In general the types of protection can be summarized to:
Dust-ignition proof
A dust ignition proof component prevents dust entering from outside. Arcs, sparks and heat generated inside of the enclosure will not be able to ignite the exterior surroundings near the component.
Explosion proof
An explosion proof component is capable to keep an internal explosion of a specific flammable air-vapor mixture within the component enclosure without releasing burning or hot gases to the external environment which may be potential explosive. The explosion proof equipment must also operate below safe temperatures.
The potentially sparking parts are encapsulated in a special house which is designed to prevent explosions by
- preventing the entry of hazardous material in potentially hazardous concentrations
- encapsulate potential hazardous materials in a encapsulation chamber capable to contain any explosion or fire, preventing to spread outside the chamber causing secondary explosions
Intrinsically Safe
An intrinsically safe component is incapable of releasing sufficient electrical or thermal energy to cause ignition of a specific hazardous substance under normal or abnormal (fault) operating conditions. (ISA-RP12.6 - Wiring Practices for Hazardous Area Instrumentation)
In simple terms this means that intrinsically safe equipment and wiring will limit electrical and thermal energy to a level below what required to cause start an explosion.
Intrinsically safe equipment operates on low power levels. Safety barriers are grounded to be effective under fault conditions and intrinsic safety is provided through voltage and current limiters. Zener diodes and resistors limiting the energy are usually mounted away from the hazardous areas. Failure to replace enclosure covers or bolts will not imperil protection.
Intrinsically safe wiring must be separated from non-intrinsically safe wiring by at least 2 inches in order to prevent the transfer of unsafe levels of energy to the hazardous area and it is vital that planning and installation of intrinsically systems are done with care and attention.
Note! Intrinsically safety can be compromised after initial installation due to improper maintenance or repair. It is important to ensure that such works are carried out properly.
Nonincendive
Nonincendive components are nonsparking and incapable of releasing sufficient electrical or thermal energy to cause ignition of a hazardous substances under normal operating conditions.
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Related Topics
- Risk, Reliability and Safety - Risk, Reliability and Safety in Process Control Systems
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Related Documents
- Chemicals and Hazard Rating Systems - The National Fire Protection Association (NFPA) hazard system for chemical materials
- Firestop Ratings - F-rating, T-rating and L-rating of firestopping systems
- Flash Point - The flash point indicates how easy a chemical may ignite and burn
- Hazardous Areas Classification - Europe - European hazardous areas classifications in zones, protection types, temperature codes and codes
- Hazardous Areas Classification - North America - North American hazardous locations classification in classes, divisions and groups
