Page 316 - Offshore Electrical Engineering Manual

CHAPTER

Hazardous Area 4

Installation

INTRODUCTION

This is not intended to be a comprehensive treatise on hazardous area installation,
but more a consideration of the pitfalls often made in selecting and installing equip-
ment suitable for locations where risks of explosive atmospheres are present. It is not
known currently how Brexit will affect the ATEX regulations, but it can be assumed
that the same explosive risks will be present, and that general trend is towards stan-
dardisation to facilitate world trade.

HAZARDOUS AREA APPLICATIONS

Much of the equipment on an offshore installation will be located in an area classi-
fied as potentially hazardous, because of the risk that flammable gases or vapours
may be present in the atmosphere and could be ignited by equipment which cre-
ates electrical sparks or, during and perhaps for some time after operation, has an
enclosure with a high enough surface temperature. This subject is covered exhaus-
tively in a multitude of standards and codes of practice, many of which are listed
in the Bibliography, and it is intended only to summarise the subject here. Those
unfamiliar with the subject are recommended to study BS EN 60079 - Explosive
atmospheres.
An explosive atmosphere is one where a mixture of air and flammable substances
in the form of gas, vapour or mist exists in such proportions that it can be exploded
by excessive temperature, arcs or sparks. The degree of danger varies with the prob-
ability of the presence of gas from location to location, and so hazardous areas are
classified into three zones as follows:
Zone 0 (more than 100 h/year) –In which the explosive gas mixture is continu-
ously present or present for long periods. The conditions in such zones are usually
regarded as too dangerous for any electrical equipment to be located in.
Zone 1 (1–100 h/year) –In which an explosive gas/air mixture is likely to occur
in normal operation.
Zone 2 (less than 1 h/year but more than 1 h/100 years) – In which an explosive
gas/air mixture is not likely to occur in normal operation and, if it occurs, will exist
for only a short time. By implication, an area that is not classified as zone 0, 1 or 2 is
deemed to be a non-hazardous area.
The numerical values for exposure time shown above are for guidance only.

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