Hazardous Area Zones - DSEAR

Hazardous Area Zones - DSEAR

Hazardous Area Zone Classification

Hazardous areas are defined in DSEAR as "any place in which an explosive atmosphere may occur in quantities such as to require special precautions to protect the safety of workers". In this context, 'special precautions' is best taken as relating to the construction, installation and use of apparatus, as given in BS EN 60079 -101.


DSEAR (The Dangerous Substances and Explosive Atmospheres Regulations of 2002) is the United Kingdom's implementation of the European Union-wide ATEX directive.

Hazardous area zone classification is a method of analysing and classifying the environment where explosive gas atmospheres may occur, typically in oil, gas, petrochemical, utility, marine and offshore sites. The main purpose is to facilitate the proper selection and installation of hazardous area electrical equipment apparatus to be used safely in that environment, taking into account the properties of the flammable materials that will be present.

DSEAR specifically extends the original scope of this analysis, to take into account non-electrical sources of ignition, and mobile equipment that creates an ignition risk.

Hazardous Area Electrical Equipment

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T&D Hazardous Area Product Overview


Hazardous Area Zone Classification

Hazardous areas are classified into zones based on an assessment of the frequency of the occurrence and duration of an explosive gas atmosphere, as follows:

  • Zone 0: A hazardous area in which an explosive gas atmosphere is present continuously or for long periods;
  • Zone 1: A hazardous area in which an explosive gas atmosphere is likely to occur in normal operation;
  • Zone 2: A hazardous area in which an explosive gas atmosphere is not likely to occur in normal operation and, if it occurs, will only exist for a short time.

Various sources have tried to place time limits on to these hazardous area zones, but none have been officially adopted. The most common values used are:

  • Zone 0: Explosive atmosphere for more than 1000h/yr
  • Zone 1: Explosive atmosphere for more than 10, but less than 1000 h/yr
  • Zone 2: Explosive atmosphere for less than 10h/yr, but still sufficiently likely as to require controls over ignition sources.

Hazardous Area Electricals DSEAR

Where people wish to quantify the zone definitions, these values are the most appropriate, but for the majority of situations a purely qualitative approach is adequate. When the hazardous areas of a plant have been classified, the remainder will be defined as non-hazardous, sometimes referred to as 'safe areas'.

The hazardous area zone definitions take no account of the consequences of a release. If this aspect is important, it may be addressed by upgrading the specification of electrical equipment or controls over activities allowed within the zone. The alternative of specifying the extent of zones more conservatively is not generally recommended, as it leads to more difficulties with equipment selection, and illogicalities in respect of control over health effects from vapours assumed to be present. Where occupiers choose to define extensive areas as Zone 1, the practical consequences could usefully be discussed during site inspection.

DSEAR sets out the link between hazardous area zones, and the electrical equipment that may be installed in that zone. This applies to new or newly modified installations. The electrical equipment categories are defined by the ATEX equipment directive, set out in UK law as the Equipment and Protective Systems for Use in Potentially Explosive Atmospheres Regulations 1996.

Standards set out different protection concepts, with further subdivisions for some types of equipment according to gas group and temperature classification. Most of the electrical standards have been developed over many years and are now set at international level, while standards for non-electrical equipment are only just becoming available from CEN.

The DSEAR ACOP describes the provisions concerning existing equipment.

There are different technical means (protection concepts) of building equipment to the different categories. These, the standard current in mid 2003, and the letter giving the type of protection are listed below.Correct selection of electrical equipment for hazardous areas requires the following information:

  • Classification of the hazardous area
  • Temperature class or ignition temperature of the gas or vapour involved If several different flammable materials may be present within a particular area, the material that gives the highest classification dictates the overall area classification. The IP code considers specifically the issue of hydrogen containing process streams as commonly found on refinery plants. Consideration should be shown for flammable material that may be generated due to interaction between chemical species.

Safe Working with Flammable Substances in Hazardous Areas - HSE

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