Analysing explosion risk

Louise Davis

Since 2003, compliance with the Dangerous Substances and Explosive Atmospheres Regulations (DSEAR) 2002 has been required for all existing and new assets. Protection against risks from fire and explosion must be addressed throughout the life of any plant. The key requirements of DSEAR outline how compliance can be achieved and demonstrated, and how to maintain an up-to-date set of documentation.

The Approved Code of Practice (ACOP) states that DSEAR risk assessments should not be carried out in isolation from those required under other legislation, such as the Management of Health and Safety at Work Regulations, and that other risk assessments, such as fire risk assessments, functional safety studies etc. may cover many of the requirements of DSEAR. The risk assessment must provide evidence that the employer is aware of all the risks associated with dangerous substances, and has applied sufficient measures to eliminate the risks or reduce them as far as practicable. The ACOP does not specify exactly how this risk assessment should be conducted or recorded, but does provide much useful guidance. 

Some key points include: that the risk assessment must record the nature of the hazard; who might be harmed, and how; the measures that are currently in place to address the risk; any additional measures that could be taken, and actions arising from the assessment of the risk. 

Before a workplace containing flammable materials comes into operation, the employer must ensure that the overall explosion safety measures are verified as being safe. This must be done by a person or organisation competent to consider the particular risks in the workplace, and the adequacy of the explosion control and other measures put in place. 

Therefore, consideration must be given to: the risks posed by dangerous substances; is the equipment and  protective systems appropriate for operation in flammable atmospheres; are there adequate procedures & processes in place to protect personnel; has the hierarchy of control been applied; and are effective emergency measures in place.

Companies may have their own risk assessment procedures and formats, with risk matrices for categorising hazardous events. These can be used for ranking risks and targeting those that require further action to bring them into the tolerable if as low as reasonably practicable (ALARP) region. At all times, the hierarchy of control should be followed: eliminate; reduce; control; and finally, mitigate. 

Risks should be eliminated wherever possible. This can be achieved by removing dangerous substances completely, or by the application of inherent safety principles. Where risks cannot be eliminated, they should be reduced as far as possible. This may be achieved by substituting dangerous substances for others with less volatile properties, or for example by using process containment to limit the potential for flammable atmospheres to form. 

The ignition of flammable atmospheres must be avoided by correct selection, installation, operation, inspection and maintenance of equipment in hazardous areas, and by controls over the generation and accumulation of static electricity and methods of controlling the work processes that are carried out in those locations. 

Since 2015 DSEAR has covered compressed gases, substances corrosive to metal, and the upper flash-point for materials classified as flammable has been raised from 55°C to 60°C. The advice regarding these substances however is that the fundamental risk associated with these materials has not changed. Provided the risks associated with these materials was already addressed under the Management of Health and Safety at Work Regulations, then the current procedures and safeguards associated with these materials can be incorporated into the DSEAR risk assessment.

Area classification 

Only when a DSEAR risk assessment has been carried out and the hierarchy of control has been applied should area classification be undertaken. This is because area classification is aimed at ensuring control of ignition sources; it identifies the areas where a residual risk of forming a flammable atmosphere exists, after everything practicable has been done to reduce the risks as far as possible. 

DSEAR documentation must be reviewed at regular intervals. The frequency of review is not defined in the regulations; it depends on the nature of the risk, and the likely degree of change. For a high hazard process, or one that is frequently reconfigured, a shorter interval between reviews would be appropriate. Also, the DSEAR documentation should be reviewed whenever significant changes occur. A Management of Change (MoC) process should include prompts to identify whether the proposed change alters the risks associated with dangerous substances, and if so, that the DSEAR risk assessment and area classification are reviewed accordingly. 

The ACOP also states that the DSEAR risk assessment should be reviewed whenever there is reason to suspect it may be invalid. This may be the case if a site has an incident involving dangerous substances. Even a near miss should prompt a review to ensure that the risks were correctly identified, with nothing overlooked, and consider whether additional safeguards need to be introduced.

If we consider the frequency at which other process safety documentation must be reviewed, that can help to influence the definition of a suitable interval. Regulation 10 of COMAH requires that safety reports are fully reviewed every five years; the Offshore Installations (Safety Case) Regulations also require a five yearly review. The British Standard ‘60079 Explosive atmospheres Part 14: Electrical installations inspection and maintenance’ specifies that fixed equipment inspection intervals should not exceed three years without the basis for the extension being documented. It therefore follows that an interval of three years can be seen as good practice and consistent with the requirements of other relevant standards. If a longer interval was justified, then no more than five years would be advised - based on typical requirements for major process safety related documentation.

In conclusion, compliance with the regulations requires a DSEAR risk assessment to be carried out, and all DSEAR documentation to be regularly reviewed and updated. Applying the hierarchy of control, ensuring risk assessments meet the key requirements of DSEAR, and defining a sensible interval for reviews enables compliance to be demonstrated and maintained.

Written by Peter Hodgson, Safety Consultant, ABB 

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