Hazardous Areas and their Classification
What is a Hazardous Area?
A potentially explosive atmospheres exist where there is a risk of explosion due to mixtures of gas/air, vapour/air, dust/air or other flammable combinations. Any area that could have a potentially explosive atmosphere is known as a Hazardous Area.
Why are Hazardous Areas Important?
Instrument engineers introduce a potential ignition source into a Hazardous Area when they locate an electrical or electronic instrument, or a electrical or electronic final element e.g. shut down valve actuators. Understanding the degree of risk, and the design of the instrument, or final element, allows the instrument engineer to minimise the likelihood of an explosion occuring.
How are Hazardous Areas Classified?
Process plants, refineries, oil and gas platforms etc are divided into Zones (European and IEC method) or Divisions (North American method) according to the likelihood of a potentially explosive atmosphere being present, e.g.
What Standards are used for Hazardous Areas Classification?
The following international standards are used to define the classification:
- EN 1127-1:1997; Explosive atmosphere - Explosion prevention and protection. Part 1: Basic concepts and methodology
- EN 60079-10:2003; Electrical apparatus for explosive gas atmospheres. Part 10: Classification of potentially explosive atmospheres
- EN 50281-3:2002; Electrical apparatus for use in the presence of combustible dust. Part 3: Classification of areas where dusts are or may be present
- NFPA 70; National Electrical Code Chapter 5 Article 500.
It is worth noting that many - though by no means all - countries outside of Europe and North America use the IEC Standards as a basis for their own national standards.
Hazardous Area Drawings
Hazardous area zones are usually marked on a drawing of the plant, the drawing being referred to as the Hazardous Area drawing. These drawings also include temperature classification information and gas group information. By using these drawings the engineer can specify instruments and equipment suitable for the area in which it is to be located.
The following pages on Control and Instrumentation.com give more detail on Hazardous Areas, ATEX and other relevant information:
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