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Explosion-proof structure

Flammable gases and steam used in factories and plants may create an explosive condition if they leak in the atmosphere and are mixed with air. If a sensor is used in such hazardous location, the sensor must be designed and manufactured so that it will not be an ignition source for flammable substances.
Equipment with this type of design is called explosion proof equipment. This page explains the explosion proof standards applicable to this equipment.


Explosion proof design, construction and standards

To make equipment explosion proof means taking preventive measures to eliminate any possible ignition sources in hazard locations that may contain flammable gases or vapors. These explosion proof standards are specified by the Ministry of Labor as the standards for explosion proof design and construction of electrical appliances.


There are two explosion proof standards in Japan.

  1. Explosion proof design standards for electrical and mechanical equipment (Notification 16 by the Ministry of Labor)
    Enacted in 1969 and the d2G4 code has been added the standard.

    The older explosion proof standard for equipment in Japan is contained in this standard.

Meaning of code labels

  • i3aG4
    The 1st character expresses the type of explosion proof design or construction (d = withstands the pressure of an explosion, i = intrinsically safe). The 2nd and 3rd characters indicate explosion classes (classified as 1, 2, 3a,3b, 3c, and 3n). The 4th and 5th characters indicate classes of ignition temperature (classified as 6 types from G1 to G6).
  • d2G4
    The first character, d, indicates the type of explosion proof design and construction: Explosion pressure proof design. The 2nd character indicates the explosion class, 2 in this case. The 3rd and 4th characters indicate the ignition temperature class, G4 in this case.
  1. Technical standard (IEC standard 79).
    This standard was established to coordinate with the international standard (IE79) created by the IEC in 1988 (and revised in 1996). It is indicated as Exia II BT6.

Meaning of code labels

  • ExiaII BT6
    The Ex in first two characters are the explosion proof code for that technical standard. The 3rd and 4th characters indicate the type of explosion proof design (d is an explosion pressure proof design, IA is an intrinsically safe explosion proof design). The 5th and 6th characters indicate the explosion class (II, IIA, IIB, IIC). The 7th and 8th characters are the ignition temperature class (6 types from T1 to T6).
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Types of explosion proof standards

There are various explosion proof standards. This page explain the standards related to our products (explosion pressure proof design and intrinsically safe explosion proof design).

  1. Pressure enduring explosion proof structure
    An enclosure for housing electronic equipment that may be an ignition source must have an explosion pressure proof design. Even if an explosion occurs inside the housing, there must not be any effect outside of the enclosure (totally enclosed housing). The housing must have the strength to withstand an internal explosion, and prevent any sparks inside the housing from coming out.
  2. Intrinsically safe explosion proof structure
    This type of design is applicable to low voltage electric equipment. The equipment must not produce electrical sparks and therefore cannot be an ignition source (and it must not produce elevated temperatures which could set off an explosion). Explosion proof electrical circuits may not generate dangerous sparks or high temperatures.

Some other explosion proof standards are: Oil injection explosion proof designs (structure to prevent ignition by immense positions possible to generate sparks), inside explosion pressure proof housings (an inert gas is sealed inside a housing to prevent ignition), and increased safety explosion proof designs (designs that enhance safety).

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