DSEAR and Hazardous Area Classification

Do you store or handle dangerous substances?  These can include flammable gases, vapours or liquids, combustible dusts, oxidising materials, compressed gases, or materials corrosive to metal.  Processing or storing dangerous substances poses a potential threat of fire, explosion or other energy-releasing events.

The Dangerous Substance and Explosive Atmospheres Regulations 2002 (DSEAR) specify the minimum requirements for protecting people from these risks.

Your site needs to:

• Prepare a suitable and sufficient risk assessment.
• Eliminate and reduce the risk from dangerous substances.
• Complete a formal Hazardous Area Classification (HAC).
• Manage ignition sources within hazardous areas.
• Establish provision to deal with accidents, incidents and emergencies.
• Provide information, instruction and training to all relevant personnel.
• Ensure dangerous substances can be identified on site.

Even without a serious incident that results in damage, injury or loss of life, non-compliance can have serious consequences, with those found in breach of DSEAR subject to heavy fines or even jail time.

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: An area in which an explosive gas atmosphere is present continuously or for long periods
• Zone 1: An area in which an explosive gas atmosphere is likely to occur in normal operation
• Zone 2: An 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 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.

Where you 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 zone definitions take no account of the consequences of a release. If this aspect is important, it may be addressed by upgrading your specification of 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 you choose to define extensive areas as Zone 1, the practical consequences could usefully be discussed during site inspection.

(Contains public sector information published by the Health and Safety Executive and licensed under the Open Government Licence).

You should plan to review your risk assessment at regular intervals. The time between reviews depends on the nature of the risk and degree of change likely in activities. It should also be reviewed if significant changes have taken place or the you conclude it is no longer valid and following an accident or dangerous occurrence.

When reviewing your risk assessment you should take the opportunity to re-examine your control and mitigation measures. This should include considering whether it is now possible to replace the substance or process with a less dangerous one. The risk  assessment should be modified if developments mean it is no longer valid. Records, where required, of significant findings should also be updated.

(Contains public sector information published by the Health and Safety Executive and licensed under the Open Government Licence).