This part of GB 3836 is concerned with the classification of areas where flammable gas or vapour or mist hazards (see Notes 1, 2 and 3) may arise and may then be used as a basis to support the proper selection and installation of equipment for use in a hazardous area.
It is intended to be applied where there may be an ignition hazard due to the presence of flammable gas or vapour, mixed with air under normal atmospheric conditions (see Note 4), but it does not apply to
a) mines susceptible to firedamp;
b) the processing and manufacture of explosives;
c) areas where a hazard may arise due to the presence of combustible dusts or fibres (refer to GB 12476.3);
d) catastrophic failures which are beyond the concept of abnormality dealt with in this part (see Note 5);
e) rooms used for medical purposes;
f) domestic premises.
This part does not take into account the effects of consequential damage.
Definitions and explanations of terms are given together with the main principles and procedures relating to hazardous area classification.
For detailed recommendations regarding the extent of the hazardous areas in specific industries or applications, reference may be made to national or industry codes relating to those applications.
Note 1: Flammable mists may form or be present at the same time as flammable vapours. Liquids not considered to be hazardous in terms of this part (due to the flash point), when released under pressure may also generate flammable mists. In such cases, the strict application of area classification for gases and vapours may not be appropriate as the basis for selection of equipment. Information on flammable mists is provided in Appendix D.
Note 2: The use of GB 3836.15 for selection of equipment and installations is not required for mist hazards.
Note 3: For the purpose of this part, an area is a three-dimensional region or space.
Note 4: Atmospheric conditions include variations above and below reference levels of 101.3 kPa and 20 °C, provided that the variations have a negligible effect on the explosion properties of the flammable materials.
Note 5: Catastrophic failure in this context is applied, for example, to the rupture of a process vessel or pipeline and events that are not predictable.
Note 6: In any process plant, irrespective of size, there may be numerous sources of ignition apart from those associated with equipment. Appropriate precautions will be necessary to ensure safety in this context. This part may be used with judgment for other ignition sources.
