Hazardous Areas Protection Techniques

Instrinsically safe systems, purged and pressurized systems, explosion-proof equipment, nonicendive circuits and components, oil immersed equipment, hermetically sealed equipment, dust-ignitionproof equipment

Hazardous areas are classified (North America)

Class I - Spaces and areas with flammable gases or vapors. Subdivided in Division 1 - where the substance referred to by class is present during normal conditions, and Division 2 - where the substance referred to by class is present only in abnormal conditions, such as a container failure or system breakdown.
Class II - Spaces and areas with combustible dusts
Class III - Spaces and areas with easily ignitable fibers or flyings

Common protection techniques in hazardous areas are:

Dust-ignitionproof equipment - excludes dust, will not permit arcs, sparks or heat to ignite exterior dust in the enclosure
Explosionproof equipment - withstands an internal explosion without igniting the external atmosphere
Hermetically sealed equipment - sealed against the external atmosphere to prevent the entry of hazardous gases or vapors
Intrinsically safe systems - electrical circuits designed not to release sufficient energy to ignite or explosive the atmosphere
Nonicendive circuits and components - designed to prevent any arc or thermal effect
Oil immersed equipment - arc producing components are immersed in oil, an arc will never reach the surface of the oil
Purged and pressurized systems - spaces and equipment are pressurized above the external atmosphere, hazardous gases and vapors are not able to enter from the enclosure

Protection Technique	Hazardous Area
	Class I		Class II	Class II
	Division 1	Division 2	Class II	Class II
Dust-ignitionproof equipment	²⁾	²⁾	¹⁾	¹⁾
Explosionproof equipment	¹⁾	¹⁾	¹⁾	¹⁾
Hermetically sealed equipment	²⁾	¹⁾	¹⁾	¹⁾
Intrinsically safe systems	¹⁾	¹⁾	¹⁾	¹⁾
Nonicendive circuits and components	²⁾	¹⁾	¹⁾	¹⁾
Oil immersed equipment	²⁾	¹⁾	¹⁾	¹⁾
Purged and pressurized systems	¹⁾	¹⁾	¹⁾	¹⁾

¹⁾ The protection technique is appropriate to the classification

²⁾ The protection technique is not acceptable for the classification