Comparing ATEX and Ex-Proof Classifications
Manufacturers can choose and install equipment for potentially explosive environments using the ATEX and ex-proof standards. Ex-Proof is used in North America and Canada whereas ATEX is utilised in Europe.
It is necessary to determine the qualities of any materials that will be present as well as the process environment. This is done in order to categorise the ignition danger of any gas and dust atmospheres and take the proper precautionary measures.
ATEX
Zones are used in the ATEX directive to categorise gas and dust atmospheres that might be explosive. The classifications vary from an ignitable state being continually present (Zones 0 and 20) to an ignitable condition being an unlikely occurrence (Zones 2 and 22).
Powder and dust are found in Zones 20, 21, and 22. Gas, vapour, and mist are found in Zones 0 and 1.
Ex-Proof
To distinguish between explosive gas and dust atmospheres, Ex-proof employs classes (1 and 2). After that, the types of gas (A, B, C, D) and dust (E, F, G) are categorised using divisions. The most popular subdivision for milling and grinding applications is G since it includes food, grains, and general dusts.
The classes are divided into divisions (1 or 2; see below) in order to determine the chance of an ignitable concentration being present.
Class 1 (A, B, C, D) gases, vapours, and mists; Class 2 (E, F, and G) powders and dusts.
Division 1: Ignitable Conditions present 10-1000 hours annually; Division 2: Ignitable Conditions present 10-100 hours annually.
Spark Sources
For an explosion to occur in an environment of combustible gas or dust, there must be an ignition source. Suitable ignition sources consist of:
High surface temperature (caused, for example, by milling and grinding) > Electrical sparks > Mechanically generated impact sparks > Mechanically generated friction sparks > electrical current discharge
IP and NEMA Ratings
Electrical enclosures must also be certified to a level that makes them safe to use in ATEX and ex-proof situations. Enclosures used in industrial applications are of the National Electrical Manufacturers Association (NEMA) and Ingress Protection (IP) categories.
While NEMA ratings (used in North America) take these factors into account along with other parameters like corrosion and construction details, an IP rating (used in Europe) solely evaluates protection against the entry of solid foreign objects and the infiltration of water. As a result, it is impossible to compare the two ratings accurately. The following is a list of the most popular IP and NEMA ratings for milling and grinding applications.
> NEMA 7: Designed to contain an internal explosion without posing a risk. > NEMA 3S / IP54: A degree of protection against dust and water sprayed from all directions. > NEMA 4X / IP66: Total protection against infiltration of dust and powerful jets of water. Intended for use in Class 1 Division 1 / Zone 0 / Zone 1. > NEMA 9: Prevents dust from entering and potential heat-generating equipment from heating the enclosure's surfaces to a degree that might cause the surrounding dust to burn.
Delete System
In order to eliminate the potential for an explosion, compressed air or inert gas is let into the enclosure. The enclosure is under positive pressure, which permits the flow of purge air or gas into the enclosure while preventing the entry of air or gas from the surrounding atmosphere.
The purging gas of choice is often nitrogen, but alternative possibilities include carbon dioxide (which isn't completely inert), argon, and helium.
