Atmospheres can be classified as:
- Non-explosive atmosphere; the atmosphere does not contain explosive elements and all types of standard products can be used.
- Explosive atmosphere; the atmosphere does contain potentially explosive elements, either gas or dust.
Explosive atmosphere is referred to as "Hazardous area" in IEC countries and "HAZLOC" in North America
Equipment for explosive atmosphere is designed, installed, operated and maintained according to International standards and local regulations dedicated to this area.
Hazardous Area or Location is defined by 4 elements:
- Class
- Zone
- Group
- Temperature Class
Explosive atmosphere
The relevant parameters below characterize the potentially explosive atmosphere:
- Frequency with which potentially explosive atmosphere may exist
- Capability of gas or dust atmosphere to create an explosion
Explosive gas and dust is classified according to its likelihood to be ignited, according to its characteristics:
- Minimum ignition energy
- Minimum ignition temperature
- Auto-ignition temperature
- Layer ignition temperature
Standards
EN 1127-1: 1997
Explosive atmospheres - Explosion prevention and protection - Part 1: Basic concepts and methodology
IEC 60079-10: 2002-06
Electrical apparatus for explosive gas atmospheres. Part 10: Classification of hazardous areas
IEC 61241-10: 2004-06
Electrical apparatus for use in the presence of combustible dust. Part 10: Classification of areas where combustible dusts are or may be present
NEC 505
National Electrical Code (issued by ANSI : American National Standards Institute and NFPA 70 : National Fire Protection Association)
These standards define the Zones:
Atmos-
phere | Zone | Presence
per year | Definition |
Gas
Dust | 0
20 | > 1000 h | Explosive atmosphere is present continuously, or for long periods or frequently |
 | | | |
Gas
Dust | 1
21 | 10 h ... 100 h ... 1000 h | Explosive atmosphere is likely to occur in normal operation occasionally |
| | | |
Gas
Dust | 2
22 | < 10 h | Explosive atmosphere is not likely to occur in normal operation but if it does, it will exist for a short period only |
| | | |
| hj | | | |
In the U.S. 'old' standard under the reference NEC 500 is still in existence; defining the area according to Division system. The new NEC with Article 505 and Article 506 includes Zone classifications, installation requirements similar to IEC standard as defined above.
| Atmosphere | HAZLOC area NEC 500 | Definition |
| Gas or Dust | Division 1 | Ignitable concentrations of gases, vapor-in-air mixtures, combustible dusts and flying fibers can exist during normal conditions |
| | |
| Gas or Dust | Division 2 | Ignitable concentrations of gases, vapor-in-air mixtures, combustible dusts and flying fibers exist during abnormal conditions |
| | |