An Ex nR or restrictive breathing enclosure removes the fuel element of an explosion by stopping any flammable gasses entering the internal enclosure. In doing so, potentially explosive gases never come into contact with hot surfaces or an ignition source potentially present inside the enclosure.
Restrictive breathing enclosures are only certified to Zone 2 hazardous areas, where the area is considered safe in normal operation with flammable gases only present in fault conditions. The technique ensures the cumulative concentration within the enclosure does not exceed the lower explosive limit for the gas or vapor concentration over short and long periods of time.
A Ex nR enclosure typically has the following characteristics:
- Lightweight metallic or non-metallic construction
- Designed to prevent flammable gases entering
- High ingress protection levels
- Tightly sealed
Restrictive Breathing Protection Concept
Where an Ex d enclosure allows for all three components required to create an explosion (oxygen, fuel, and ignition source), an Ex nR restrictive breathing enclosure removes the fuel by keeping out flammable gasses.
An Ex nR enclosure should meet IEC 60079‐15 standards for restrictive breathing. This means arcing components in a Zone 2 environment can be used without the need for flameproof equipment.
Ex nR enclosures are subjected to temperature rise tests and ingress testing to determine the amount of gas present inside the enclosure. If the enclosure is found to restrict the air flow both in and out, it is determined to be restrictive breathing by the defined standards.
An Ex nR enclosure is very well sealed, ensuring that the enclosure does not aspirate in a flammable gas during the time it could be exposed to it. It is only a Zone 2 rather than a Zone 1 protection concept as the risk of flammable gas in Zone 1 is far higher, increasing the likelihood the seal could eventually aspirate some flammable gas.
Cable Gland Connections
The Ex nR enclosure cable glands interface also needs assessing to ensure the seal is maintained for restricted breathing. IEC 60079‐0 states that all glands to be used in conjunction with Ex nR equipment must be suitable and certified to Ex nR protection concept.
There are a range of minimum requirements all Ex n cable glands must meet to ensure compliance with IEC 60079-0 standards.
These include thermal endurance testing, cable pull out resistance, but in relation to the nR protection concept for compatibility with any restrictive breathing enclosures, cable glands must adhere to special testing under IEC 60079-15 for cable and cable entry to ensure seals are sufficient to stop flammable gases aspirating inside the enclosure. The testing looks to determine if the inner seal is airtight in two directions to achieve compliance under Ex nR protection concepts.
Extronics specialise in developing and manufacturing ATEX, IECEx, and North American certified equipment for use in hazardous areas, and rugged industrial products for harsh environments. We serve customers around the world from industries such as oil and gas, chemical, pharmaceutical, and mining.
For more information, please speak to a member of our team by emailing us at firstname.lastname@example.org or calling us on +44 (0)1606 738 446.