An Ex nR or restrictive breathing enclosure eliminates the fuel element of an explosion by preventing any flammable gasses from escaping into the internal enclosure. Subsequently, potentially explosive gases do not come into contact with an ignition source or hot surfaces that may be present inside the enclosure.
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Restrictive breathing enclosures are certified to Zone 2 hazardous areas, where the area is judged to be safe in standard operational procedures with flammable gases only present in fault conditions. The method ensures the accruing concentration within the enclosure does not exceed the lower explosive limit for the gas or vapor concentration over a reduced or extended period of time.
An Ex nR enclosure tends to have the following characteristics:
- Lightweight metallic or non-metallic construction
- High ingress protection levels
- Tightly sealed
- Designed to prevent flammable gases from entering
Restrictive Breathing Protection Concept
Where an Ex d enclosure fosters all three elements necessary to produce an explosion (oxygen, fuel, and ignition source), an Ex nR restrictive breathing enclosure eliminates the fuel by restricting any flammable gasses.
An Ex nR enclosure should match IEC 60079‐15 standards for restrictive breathing. Therefore, arcing components in a Zone 2 environment can be utilized without necessitating the use of flameproof equipment.
Ex nR enclosures are put through temperature rise tests and ingress testing to regulate the amount of gas residing inside the enclosure. If it is discovered that the enclosure restricts the flow of air both in and out, it is declared to be restrictive breathing by the required standards.
An Ex nR enclosure is usually extremely well sealed, making sure that the enclosure does not draw in any flammable gas during the time it could be subjected to it. Rather than being designated Zone 1, it is only a Zone 2 protection concept as the risk of flammable gas in Zone 1 is much greater, increasing the probability that the seal could aspirate some flammable gas in due course.
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Cable Gland Connections
Assessment of the Ex nR enclosure cable glands interface is necessary to ensure the seal is well maintained for restricted breathing. IEC 60079‐0 outlines that all glands used in combination with Ex nR equipment must be certified and suitable Ex nR protection concept.
There are a variety of minimum requirements all Ex n cable glands must meet to make sure they comply with IEC 60079-0 standards. These include cable pull out resistance and thermal endurance testing.
However, with regards to the nR protection concept to be compatible with any restrictive breathing enclosures, cable glands must be subjected to special testing under IEC 60079-15 for cables and cable entry. This guarantees seals are able to prevent flammable gases from aspirating inside the enclosure. The testing sets out to determine if the inner seal is airtight in both directions to accomplish compliance under Ex nR protection concepts.
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About Extronics
Extronics specialize in manufacturing and developing ATEX, IECEx, and North American certified equipment for use in hazardous areas and robust industrial products for tough environments. The company serves a global customer database across various industries, including oil and gas, pharmaceutical, chemical, and mining.
This information has been sourced, reviewed and adapted from materials provided by Extronics Ltd.
For more information on this source, please visit Extronics Ltd.