IECEX and ATEX are important safety certification for process analyzers being installed in hazardous environments. The NIR-O has a maximum protection rating of Zone 1, Group IIB+H2, T4. This protection rating is offered with either ATEX and IECEX certification.
What is the difference between Class 1 Div 1 Zone 1 and Class 1 Div 2 Zone 2 protection?
The major difference between Class 1 Div 1, Zone 1 and Class 1 Div 2, Zone 2 IECEX certification is in the assumption of risk. Div 1 or Zone 1 assumes that hazardous gases are always present in the environment. Div 2 or Zone 2 assumes that hazardous gases may be present in the environment, but are unlikely.
To achieve Div 1 or Zone 1 protection rating, a process analyzer must have a clean air purge system that keeps the enclosure under positive pressure. Additionally, if the pressure drops, an interlock must trigger which shuts off the analyzer and prevents the system from exposing the combustible gases to an electrical ignition source. The electronics cannot result until pressure is restored and for some amount of time. This is often referred to as an X-purge.
To achieve Div 2 Zone 2 protection rating, a process analyzer still requires a clean air purge. However, the airflow only must maintain positive pressure. If the pressure inside of the enclosure is lost the analyzer must alarm, but may remain powered on to collect data. This is often referred to as a Z-purge.
Understanding the ATEX Zone rating – the Petrol Station analogy
Explaining ATEX Group Markings
The gas and dust protections are defined by groups. A group III rating means that the enclosure is only rated to protect against dust infiltration. A group II rating means that the enclosure is protected against both dust and gas. The lowest gas protection is IIA the best gas protection rating is group IIC.
Group IIA – protection is adequate to prevent ignition of propane gas in the environment.
Group IIB – protection is adequate to prevent ignition of ethylene gas in the environment.
Group IIB+H2 – protection is adequate to prevent ignition of hydrogen gas in the environment.
Group IIC – protection is adequate to prevent ignition of acetylene gas in the environment.
ATEX and IECEX group markings have equivalent IP or Ingress Protection ratings. Guided Wave process analyzers all have NEMA 4 or IP 66 ratings enclosures as part of the protection design for hazardous and explosive environments.
What does the T marking mean in IECEX?
The T stands for the maximum external surface temperature that the analyzer must not exceed. This portion of the specification is to prevent the surface of the analyzer enclosure from igniting combustible molecules in the environment. For example, Ethyl Nitrate will explode if it comes into contact with a heat source or object above 90 ºC. Any analyzer that is going to be installed in an environment containing Ethyl Nitrate must be rated for T6 and never exceed a surface temperature above 85 ºC. The limit for T4 is that the outside of the analyzer will never be hotter than 135 ºC. All Guided Wave analyzers have a T4 rating they are suitable for installation in petrochemical and refinery facilities
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