This part of GB 12476 is concerned with the classification of areas where explosive dust/air mixtures and combustible dust layers are present, in order to permit the proper selection of equipment for use in such areas.
In this part, explosive dust atmospheres and combustible dust layers are treated separately. In Clause 4, area classification for explosive dusts clouds is described, with dust layers acting as one of the possible sources of release. In Clause 7, the hazard of dust layer ignition is described.
This part assumes effective housekeeping based on a system of cleaning for the plant.
The principles of this part can also be followed when combustible fibres or flyings may cause a hazard.
This part is intended to be applied where there can be a risk due to the presence of explosive dust/air mixtures or combustible dust layers under normal atmospheric conditions.
It does not apply to
——underground mining areas;
——areas where a risk can arise due to the presence of hybrid mixtures;
——dusts of explosives that do not require atmospheric oxygen for combustion, or to pyrophoric substances;
——catastrophic failures which are beyond the concept of abnormality dealt with in this part (see Note 1);
——any risk arising from an emission of flammable or toxic gas from the dust.
This part does not take into account the effects of consequential damage following a fire or an explosion.
Note 1: Catastrophic failure in this context is applied, for example, to the rupture of a storage silo or a pneumatic conveyor.
Note 2: In any process plant, irrespective of size, there can be numerous sources of ignition apart from those associated with equipment. Appropriate precautions will be necessary to ensure safety in this context, but these are outside the scope of this part.
Foreword I
Introduction II
1 Scope
2 Normative References
3 Terms and Definitions
4 Area Classification for Combustible Dusts
4.1 General
4.2 Area Classification Objectives for Explosive Dust Atmospheres
4.3 Area Classification Procedure for Explosive Dust Atmospheres
5 Sources of Release for Explosive Dust Atmospheres
5.1 General
5.2 Identification of Sources of Release
6 Zones for Explosive Dust Atmospheres
6.1 General
6.2 Zones for Dusts
6.3 Examples of Zones for Explosive Dust Atmospheres
6.4 Extent of Zones for Explosive Dust Atmospheres
7 Dust Layer Hazard
8 Documentation
8.1 General
8.2 Drawings, Data Sheets and Tables
Annex A (Informative) Area Classification Application
A.1 Bag Emptying Station within a Building and without Exhaust Ventilation
A.2 Bag Emptying Station with Exhaust Ventilation
A.3 Cyclone and Filter with Clean Outlet outside Building
A.4 Drum Tipper within a Building without Exhaust Ventilation
Annex B (Informative) Risk of Fire from Hot Surface Ignition of Dust Layer
B.1 Rule 1—Dust Layers up to 5 mm
B.2 Rule 22—Dust Layers above 5mm and up to 50mm Thickness
B.3 Rule 3-Dust Layers of Excessive Thickness
B.4 Rule 44—Laboratory Investigation
Annex C (Informative) Housekeeping
C.1 Introduction
C.2 Levels of Housekeeping
