Last edit: 03/03/2023
The last edition of the ATEX standard was published as EN on December 1, 2015.
The ATEX standard EN 60079-10-2 is concerned with the identification and classification of areas where such hazards from dust can arise. It sets out the essential criteria against which the ignition
hazards can be assessed and gives guidance on the design and control parameters which can be used in order to reduce such a hazard. General and special criteria are given for the
process of identification and classification of hazardous areas.
Among the news introduced in the ATEX standard is a guidance on hybrid mixtures (Annex C). A hybrid mixture is a combined mixture of a flammable gas or vapour with a combustible dus or combustible flyings. This hybrid mixture may behave differently than the gas / vapour or dust individually. A hybrid mixture may form an explosive atmosphere outside the explosive limits of the gas / vapour or explosive concentrations for the dust individually. It is recommended that a hybrid mixture is considered to be explosive if the concentration of the gas / vapour exceeds 25 % of the LEL for the gas / vapour.
The hazards presented by dusts are as follows:
- the formation of a dust cloud from any source of release, including a layer or accumulation, to form an explosive dust atmosphere;
- the formation of dust layers, which are not likely to form a dust cloud, but may ignite due to self-heating or exposure to hot surfaces or thermal flux and cause a fire hazard or overheating of equipment. The ignited layer may also act as an ignition source for an explosive atmosphere.
a) The first step is to identify whether the material is combustible and, for the purpose of assessment of ignition sources, determine the material characteristics. Parameters such as particle size, moisture content, cloud and layer minimum ignition temperature and electrical resistivity shall be considered. The appropriate dust group; Group IIIA for combustible flyings, Group IIIB for non-conductive dust, or Group IIIC for conductive dust shall be identified.
b) The second step is to identify items of equipment where explosive dust mixtures may be contained or sources of dust release can be present. It may be necessary to consult process line diagrams and plant layout drawings. This step should include the identification of the possibility of the formation of dust layers.
c) The third step is to determine the likelihood that dust will be released from those sources and thus, the likelihood of explosive dust atmospheres in various parts of the installation.