ISA TR12.24.01

SAME AS IEC 60079-10 *TECHNICAL REPORT

ISA-TR12.24.01 is concerned with the classification ofhazardous areas where flammable gas or vapor risks may arise, inorder to permit the proper selection and installation of apparatusfor use in such hazardous areas (see Notes 1 and 4).

It is intended to be applied where there may be a risk ofignition due to the presence of flammable gas or vapor, mixed withair under normal atmospheric conditions (see Note 2), but it doesnot apply to:

a) mines susceptible to firedamp;

b) the processing and manufacture of explosives;

c) areas where a risk may arise due to the presence of ignitabledusts or fibers;

d) catastrophic failures which are beyond the concept ofabnormality dealt with in this recommended practice (seeNote 3);

e) rooms used for medical purposes;

f) areas where the presence of flammable mist may give rise toan unpredictable risk and which require special consideration (seeNote 5).

This recommended practice does not take into account theeffects of consequential damage.

Definitions and explanations of terms are given together withthe main principles and procedures relating to hazardous areaclassification.

For detailed recommendations regarding the extent of thehazardous areas in specific industries or applications, referencemay be made to the codes, standards, or recommendedpractices relating to those industries or applications.

NOTE 1 — For the purpose of this standardrecommended practice, an area is a three-dimensional region orspace.

NOTE 2 — Atmospheric conditions includevariations above and below reference levels of 101.3 kPa (1.013mbar) and 20 °C (293 K), provided that the variations have anegligible effect on the explosion properties of the flammablematerials.

NOTE 3 — Catastrophic failure in this contextis applied, for example, to the rupture of a process vessel orpipeline, and such other events that are notpredictable.

NOTE 4 — In any facility ,irrespective of size, there may be numerous sources of ignitionapart from those associated with electrical apparatus. Appropriateprecautions will be necessary to ensure safety in this context.This recommended practice may be used with judgment forother ignition sources.

NOTE 5 — Mists may form or be present at thesame time as flammable vapors. This may affect the way flammablematerial disperses and the extent of any hazardous areas. Thestrict application of area classification for gases and vapors maynot be appropriate because the flammability characteristics ofmists are not always predictable. Whilst it can be difficult todecide upon the type and extent of zones, the criteria applicableto gases and vapors will, in most cases, give a safe result.However, special consideration should always be given to the dangerof ignition of flammable mists.

Purpose

The purpose of this recommended practice is to provideguidelines for classifying hazardous (classified) locations for theselection and installation of electrical equipment. Basicdefinitions given in the 1995 edition of IEC 79-10, Electricalapparatus for explosive gas atmospheres, Classification ofhazardous areas, have been followed in developing this recommendedpractice. This publication is only a guide and requires theapplication of sound engineering judgment.

Electrical installations in areas where flammable liquids orgases are produced, processed, stored or otherwise handled can besuitably designed if the locations of potential sources of releaseand accumulation are clearly defined. Once a location has beenclassified, requirements for electrical equipment and associatedwiring should be determined from applicable publications.Applicable publications may include NFPA No. 70 (NEC) or API RP14F. Reference Section 1.2 for other possible applicablepublications.

Edition:

98

Published:

01/01/1998

Number of Pages:

66

File Size:

1 file , 860 KB