This part of IEC 60079 is concerned with the identification and classification of areas where explosive dust atmospheres and combustible dust layers are present, in standard atmospheric conditions, in order to permit the proper assessment of ignition sources in such areas.
In this standard, explosive dust atmospheres and combustible dust layers are treated separately. In Clause 4, area classification for explosive dust clouds is described, with dust layers acting as one of the possible sources of release. InClause 7 other general considerations for dust layers are described.
The examples in this standard are based on a system of effective housekeeping being implemented in the plant to prevent dust layers from accumulating. Where effective housekeeping is not present, the area classification includes the possible formation of explosive dust clouds from dust layers.
The principles of this standard can also be followed when combustible fibres or flyings might cause a hazard.
NOTE 1 Atmospheric conditions include variations in pressure and temperature above and below reference levels of 101,3 kPa (1 013 mbar) and 20 °C (293 K), provided that the variations have a negligible effect on the explosive properties of the combustible material. Air with normal oxygen content, typically a volume fraction of 21 % is assumed.
It does not apply to
a) underground mining areas;
b) dusts of explosives that do not require atmospheric oxygen for combustion such as pyrophoric substances, propellants, pyrotechnics, munitions, peroxides, oxidizers, water-reactive elements or compounds, or other similar materials;
c) catastrophic failures or rare malfunctions which are outside the conditions dealt with in this standard;
d) rooms used for medical purposes;
e) domestic premises;
f) where a hazard is due to the presence of flammable gas or vapour, but the principles can be used in the assessment of a hybrid mixture (see also IEC 60079-10-1).
NOTE 2 Additional guidance on hybrid mixtures is provided in Annex E.
This standard does not consider the effects of consequential damage following a fire or an explosion.
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