Definition:
A hazardous area is a location where flammable gases, dusts, or fibers may accumulate in sufficient quantities to ignite or explode. These areas are common in industries such as oil & gas, chemical processing, wastewater treatment, and grain handling. Designating and managing hazardous areas is critical for protecting personnel and infrastructure from ignition sources.
Hazardous area classification is a discipline of its own, governed by regulatory codes and standards. In the U.S., the National Electrical Code (NEC) NFPA 70 Article 500 defines Class/Division systems. Globally, the IEC Zone system (IEC 60079 series) is more common. These systems dictate what types of equipment may be installed, how they must be certified, and what design practices must be followed.
Hazardous area classification is not functional safety, but the two often coexist and some of the same terms and players are involved. When hazardous areas are present, they inform the selection and certification of field devices, such as instruments and final elements, that may also participate in safety instrumented systems (SIS). Those components may require both hazardous location approvals (like ATEX, IECEx, or UL) and a SIL capability rating under IEC 61508.
Functional safety focuses on how systems respond to process deviations, while hazardous area compliance addresses ignition prevention. Together, they reduce overall risk, but they operate under distinct regulatory and engineering frameworks.
Key Points:
- Hazardous areas contain ignitable gases, dusts and fibers
- Governed by standards like NEC §500, IEC 60079, ATEX, and IECEx.
- Not part of the IEC 61511 functional safety framework.
- May impact equipment selection for SIS but is a separate compliance path.
- Functional safety addresses process risk; hazardous areas address ignition risk.
Example:
A petrochemical facility has various SIFs. One SIL 2 SIF has a final element that is in a hazardous area due to methane, but the instrument and logic solver are not. The hazardous area program determines the final element area to be Zone 2. When procuring the final element the engineer selects not only a SIL 2 valve assembly, but also one that is Zone 2. It must be both. The instrument and the logic solver can be SIL 2 but rated unclassified.
See also: final element
Cited Source:
- NEC §500 – National Electrical Code: Hazardous Locations
- IEC 60079 series – Explosive atmospheres
- ATEX Directive 2014/34/EU
- IECEx Certification System