Page 264 - Handbook of Electrical Engineering

10

Hazardous Area Classification

and the Selection of Equipment

10.1 HISTORICAL DEVELOPMENTS

Some of the earliest work on the subject of hazardous area classification was documented by the API,
IP and BS institutions, and the chemical manufacturing company ICI. Their particular documents are
given in Table 10.1.

Some of these documents have become obsolete or little used, e.g. BS229, BS1259, Electrical
Installations in Flammable Atmospheres (from ICI) whilst others have been up-dated several times.
New standards have also been introduced. A similar situation exists with the international standards
pertaining to the selection of equipment for hazardous areas, many more references could be quoted.

In the period up to about 1980 it was common practice for senior electrical engineers to
determine the various hazardous areas on a site. This was historically due to the fact that electrical
power equipment was the easiest to identify as a possible cause of ignition. It would often be the
first equipment to be investigated when an incident occurred.
The modern approach has changed for the better. It is now the more common practice that
senior mechanical and senior process engineers manage this task in co-operation with electrical,
instrumentation and safety personnel. The emphasis in this approach is the clear identification of
possible sources of leaking gas or vapour. This is by nature more within the experience of mechanical
and process engineers because they tend to be mainly responsible for the layout of the plant at the
start of a project. Thereafter the electrical engineers select the type and design of manufactured
equipment to suit the hazardous areas that have been identified on scaled drawings.

10.2 PRESENT SITUATION

For the classification of hazardous areas the notable standards that are most frequently used are
IEC60079 Part 10 for UK and Europe, BS5345 Part 2 for UK only, API 500 A for USA. Although
the territories of origin are given it is found in practice that an oil company operating in a par-
ticular country may adopt any one or a combination of standards to comply with the governing
rules of the country e.g. European standards are adopted in Abu Dhabi and Qatar, whereas the
standards of the USA are preferred in Saudi Arabia. A similar situation exists in the Far East
for example.

Handbook of Electrical Engineering: For Practitioners in the Oil, Gas and Petrochemical Industry. Alan L. Sheldrake
 2003 John Wiley & Sons, Ltd ISBN: 0-471-49631-6