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Explosion Proof vs. Intrinsically Safe

Definition - Hazardous area, or explosive atmosphere?

A hazardous area is a location where flammable vapors, such as gas, or 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 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 to ATEX and IECEx standards.

Comparison... Explosion Proof vs. Intrinsically Safe.

"Explosion Proof" means that a housing has been designed, usually of stainless steel or cast aluminium, to prevent ignition within the explosive area. The 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 temperature to exeed ignition temperature of gases or vapors within a specific Group rating.

"Intrinsically Safe": One of the more recent types of protection against explosion hazards by electrical apparatus and installations is called "intrinsic safety". The most common types of protection were conceived for electrical power engineering applications and handheld, portable devices. As a result of increasing automation in hazardous areas, there has been an ever growing demand for explosion-protected measurement and control devices.

Intrinsically safe circuits only have a low energy content that is normally not sufficient to ignite an explosive mixture. Thus, for these circuits, the ceation of a type of protection that makes use of this physical principle is the obvious solution.

Some sub definitions:

  • Intrinsic safety "i": A type of protection based on the restriction of electrical energy within apparatus and of interconnecting wiring exposed to the potentially explosive atmosphere to a level below that which can cause ignition by either sparking or heating effects.
  • Intrinsically safe circuit: A circuit in which any spark or any thermal effect produced in the conditions specified in the standard "EN 60079-11", which include normal operation and specified fault conditions, is not capable of causing ignition of a give explosive atmosphere.
  • Intrinsically safe apparatus: Electrical apparatus in which all the circuits are intrinsically safe circuits.
  • Safety barriers with diodes: Assemblies incorporating shunt diodes or diode chains (including Zener diodes) protected by fuses or resistors or a combination of both, manufactured as an individual apparatus rather than as part of a larger apparatus.

A classification ratings 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 part 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 of 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).

It is the user's responsibility to ascertain if a particular product is safe and without risk to health and safety by virtue of its location in a hazardous area, i.e. classification of zones, gas groups, ignition temperatures, etc. Both the specifier and user should be thoroughly familiar with standard mentioned on this sites or any document within.

Whilst every care has been taken in the compilation of this document, we regrets that it cannot accept responsibility for any errors or omissions contained herein. Readers should not rely upon the information contained in this document or site without seeking specific safety advice and ensuring that their own particular circumstances are in accordance with the matters set out.

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