Define the Hazard

Ex Triangle In order to prevent an explosion the aspects of the potential hazard must be defined in both type and degree, this allows us to implement measures to prevent the explosion.
From basic ignition triangle which shows the 3 parts which are required to be present for an explosion to occur

  1. By definition oxygen (air) is present as if it were not Atex would not strictly speaking apply1
  2. The probability of fuel being present i.e. Hazardous area zone should be assessed
  3. Ignition source parameters should be considered for both hot surface and Spark.

Putting aside the Air/Oxygen aspect the first stage of any assessment is to assess the probability of a fuel being present i.e the area to be assessed is classified into ZONEs as defined in EN 60079‑10.

The the explosive nature of the fuel2 then needs to be assessed with 2 properties being critical.

  • the host surface ignition temperature3
  • the spark energy required for ignition

These 2 parameters are not connected and must be independently evaluated for each fuel likely to be present.


Groups

Due to the nature of the environment Mining and Surface industries are treated differently, and equipment is classified into 2 groups within the Atex Coding relating to the explosive atmosphere for which it is to be used, Group I for mining and Group II for surface use with an additional Group ||| for surface Dust.


Notes


  1. The EN standards generally relate to NTP (Normal Temperature & Pressure) unless specifically detailed, conditions such as enriched Oxygen are outwith the scope although it is feasible that a Test house could issue certification outside those conditions based on their own criteria.. 

  2. Multiple gases are usually straightforward and based on the worst case scenario i.e. gases with lowest ignition temperature and ignition energy except in a few cases where the gas source is a mix and therefore the may be calculated on that mix Hybrid environments i.e. gas and dust must be assessed as a single entity and usually will be a special case regarding certification. 

  3. Ignition parameters are determined by test and will vary for an individual fuel depending on the source of those figures. 

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