Knowledge Base:  
Explosion Proof vs. Intrinsically Safe
Last Updated: 05/10/2013

First, let's define a hazardous area, or explosive atmosphere?  

A hazardous area is a location where flammable vapors, such as gas, or a concentration of fine dust particles, grains or fibers may be present. This includes, but is not limited to, chemical and petro-chemical refineries and process plants, paper mills, sugar refineries, coal mines, and much more. The use of electronic equipment in a hazardous area requires strict certification. In an atmosphere where potential gas vapors or fine dust is present, all electronic devices must be designed and properly certified according to ATEX and IECEx standards.

Now the comparison... Explosion Proof vs. Intrinsically Safe

“Explosion Proof” means that a housing has been designed, usually of stainless steel or cast aluminum, to prevent ignition within the explosive area. These housings, or containers, have the strength to contain an explosion if flammable gases or combustible particles penetrate the housing where ignition occurs. These explosion proof housings also prevent any surface temperatures to exceed ignition temperature of the gases or vapors within a specific Group rating.

“Intrinsically Safe” is a more common method of handheld, portable devices. Intrinsic safety is achieved by limiting the energy and surface temperature of a device during normal operation, or during foreseeable fault conditions, to an insufficient level to ignite an explosive environment.

A classification rating is earned by passing the rigorous approval process of a recognized entity. Upon approval, the exact approved hazardous situations are displayed on the label attached to the unit. The European ATEX approval is accepted in many parts of the world (checking with the end-user customer is the only way to be sure outside Europe). Certification from Factory Mutual (FM) and Canadian Standard Association (CSA) are the most common approval in North America.

Below defines how certain gases or vapors are classified, and how they are present in a certified area.

Class I: Gases and vapors

Division 1: Gases or vapors are usually present or may be present at any time in sufficient concentrations for an explosion hazard.

Division 2: Gases or vapors are not normally present and are present only in the event of a leak in some kind of containment vessel or piping, again in potentially hazardous concentrations.

Groups A, B, C, D: Groups of atmospheres categorized by the volatility and/or ignition temperatures. “A” is the most hazardous and “D” is the least hazardous group for gases and vapors.

  • Group A: Atmospheres containing acetylene.
  • Group B: Atmospheres containing hydrogen or gases or vapors of equivalent hazard.
  • Group C: Atmospheres containing ethyl-ether vapors, ethylene, or cyclo-propane.
  • Group D: Atmospheres containing gasoline, hexane, naptha, benzene, butane, propane, alcohol,  acetone, benzol, lacquer solvent vapors, or natural gas (methane)

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