Explosive gas atmosphere
An explosive gas atmosphere is created under atmospheric conditions when air is mixed with flammable substances in the form of gas or vapour, which after ignition, permits self-sustaining flame propagation.
Explosive dust atmosphere
An explosive dust atmospheres is created under atmospheric conditions when air is mixed with flammable substances in the form of dust, which after ignition, permits self-sustaining propagation.
Hazardous area
A hazardous area is identified when an explosive atmosphere is present or may be expected to be present.
Hazardous area classification is a method of analysing and classifying where explosive gas /vapour or dust or hybrid mixture may occur. In addition to analysing process, plant, instrumentation, the classification also takes into account the ignition characteristics of gas/vapour or dust, hybrid mixture such as ignition energy ( Gas Group or Dust Group) and ignition temperature (temperature class or maximum surface temperature).
This classification is important to facilitate the proper selection and installation of equipment to be used safely in that area.
Classification of hazardous area is carried out by competent person in accordance with IEC 60079-10-1 or AS/NZS 60079.10.1 for explosive gas/vapour and IEC 60079-10-2 or AS/NZS 60079.10.2 for explosive dust.
Grouping of electrical and non-electrical equipment
Use these tables for Australia and IEC Grouping by Equipment Protection Level (EPL).
Gas and vapours
| Typical Locations | Gas Group | Reference Gases | EPL - Very High | EPL - High | EPL - Enhanced |
|---|---|---|---|---|---|
| Underground coal mines | I | Methane | Ma | Mb | - |
Gas, petrol, kerosene and gasoline pipelines and distribution centres; aircraft refuelling and hangars; automotive refuelling stations; liquefied natural gas (LNG) plants | IIA | Propane | Ga | Gb | Gc |
Oil, gas and petrochemical refineries; rigs and processing plants; painting and surface coating industries | IIB | Ethylene | Ga | Gb | Gc |
Chemical production and processing plants | IIC | Acetylene & Hydrogen | Ga | Gb | Gc |
Gas and vapour classification
Use this table for gas and vapour classification.
For more information, refer to standard AS/NZS or IEC 60079-20-1, Explosive atmospheres - Material characteristics.
| Gas | Relative density (AIR=1) | Lower flammable level (Vol %) | Upper flammable level (Vol %) | Auto-ignition temp 0C | Group | MESG | MIC ratio |
|---|---|---|---|---|---|---|---|
| Methane Industrial (max 25% V/V H2) | - | 4.4 | 17 | 600 | IIA | 1.12 | 1 |
| Methane firedamp | 0.55 | 4.4 | 17 | 595 | I | 1.14 | - |
| Propane | 1.56 | 1.7 | 10.9 | 450 | IIA | 0.92 | 0.82 |
| Ethylene | 0.97 | 2.3 | 36 | 440 | IIB | 0.65 | 0.53 |
| Hydrogen | 0.07 | 4 | 77 | 560 | IIC | 0.29 | 0.25 |
| Acetylene | 0.9 | 2.3 | 100 | 305 | IIC | 0.37 | 0.28 |
| Oxybisethane (diethyl ether) | 2.55 | 1.7 | 39.2 | 175 | IIB | 0.87 | 0.88 |
| Ethanol | 1.59 | 3.1 | 19.0 at 60°C 27.7 at 100°C | 400 | IIB | 0.89 | 0.88 |
| Carbon disulfide | 2.64 | 0.6 | 60 | 90 | IIC | 0.34 | 0.39 |
| Carbon monoxide | 0.97 | 10.9 | 74 | 607 | IIB | 0.84 | - |
Dust
Dust classification:
- Combustible flyings are solid particles, including fibres, where one dimension is greater than 500µm, which may form an explosive mixture with air in standard atmospheric pressure and temperature.
- Non-conductive dust is combustible dust with electrical resistivity greater than 1 kΩm.
- Conductive dust is combustible dust with electrical resistivity equal or less than 1 kΩm.
| Typical locations | Dust Group | Dust Type | EPL - very high | EPL - High | EPL - Enhanced |
|---|---|---|---|---|---|
Woodworking areas | IIIA | Combustible flyings | Da | Db | Dc |
Woodworking areas; sugar refineries; grain handling and storage and processing (flour-milling industry | IIIB | Combustible flyings Non-conductive dust | Da | Db | Dc |
Light metal working, where metal dust and fine particles can appear | IIIC | Combustible flyings Non-conductive dust and conductive dust | Da | Db | Dc |