IS 5572 : 2009 Classification of Hazardous Areas (Other than Mines) Having Flammable Gases and Vapours for Electrical Installation

1 Scope

1.1 This standard provides guidance on the classificationof areas where flammable gas or vapour risks may arise in order to permit the proper selection of electrical apparatus for use in such areas (seeNotes 1 and 2 of 1.4).

1.2 It is intended for application in all industries where there may be a risk due to the presence of flammable gas or vapour, mixed with air under normal atmosphericconditions (see Note 3 of 1.4), but does not apply to,

a) mining applications susceptible to fire damp;

b) processing and manufacture of explosives;

c) areas where risks may arise due to thepresence of ignitable dusts or fibres;

d) catastrophic failures, which are beyond theconcept of abnormality dealt with in thisstandard (see Note 4 of 1.4);

e) ignition sources other than those associatedwith electrical apparatus (see Note 5 of 1.4);

f) areas where pyroforic substances are handled;

g) rooms used for medical purposes; and

h) domestic premises.

This standard does not take into account the effects ofconsequential damage.

1.3 Definitions and explanations of terms are giventogether with the main principles and proceduresrelating to area classification.

1.4 The objective of area classification is the notionaldivision of a plant into zones within which thelikelihood of the existence of an explosive gas/airmixture is judged to be high, medium, low or so lowas to be regarded as negligible. An area classificationestablished in this way provides a basis for the selectionof electrical apparatus that is protected to a degreeappropriate to the risk involved. The type of protectionof the apparatus selected will be such that the likelihoodof it being a source of ignition, at the same time as thesurrounding atmosphere is explosive, is accepted asbeing small.

NOTES

1 Flammable materials for the purpose of area classificationinclude,

a) petroleum having flash point below 65?C or anyflammable gas or vapour in a concentration capable ofignition; and

b) petroleum or any flammable liquid having flash pointabove 65?C where likely to be refined, blended, handledor stored at or above its flash point.

2 For the purpose of this standard an area is a three dimensionalregion or space.

3 Normal atmospheric conditions include variations above andbelow reference levels of 101.3 kPa (1 013 mbar) and 20?Cprovided the variations have a negligible effect on the explosionproperties of the flammable materials.

4 Catastrophic failures in this context is applied, for example,to the rupture of a process vessel or pipeline and events thatare not predictable.

5 In any plant installation irrespective of size there may benumerous sources of ignition apart from those associated withelectrical apparatus. Additional precautions may be necessaryto ensure safety in this aspect but these are outside the scopeof this standard.

6 Mists may form or be present at the same time as flammablevapours. This may affect the way flammable material dispersesand the extent of any hazardous areas. The strict applicationof area classification for gases and vapours may not beappropriate because the flammability characteristics of mistsare not always predictable. Whilst it can be difficult to decideupon the type and extent of zones, the criteria applicable togases and vapours will, in most cases, give a safe result.However, special consideration should always be given to thedanger of ignition of flammable mists.

7 For the purpose of this standard, the terms flammable andexplosive may be considered as synonymous.

2 References

The following referred standard is indispensable for the application of this standard: