Dangerous Substances and Explosive Atmospheres Regulations (DSEAR)
What is the purpose of this legislation?
DSEAR replaced various items of legislation in 2002, consolidating regulation relating to the management and control of risks to safety posed by:
- substances corrosive to metals.
Some of the largest fires in the UK have been due to inadequately controlled ignition sources in areas where an explosive atmosphere is or becomes present, caused, for example, by highly flammable liquids or combustible dusts. Where all of the necessary measures have been taken to properly comply with DSEAR then the risk of a fire and explosion can usually be satisfactorily controlled, but if they are not in place then lives and business can be put at serious risk.
Who is responsible for compliance?
Employers and the self-employed. Complying with DSEAR is required for most business in Great Britain – there are just a few exceptions.
What needs to be done?
Establish what dangerous substances are being used or stored on the premises and have a risk assessment carried out by a competent person with the right knowledge and experience. This assessment needs to consider:
- the properties of the substance, for example explosive, oxidising, highly flammable, corrosive to metal;
- the quantity involved;
- how the substance is used, processed, moved and stored;
- the likelihood that an explosive atmosphere may occur;
- the extent to which ignition sources (including electrostatic discharge, i.e. static electricity) are present in the area;
- the scale of the likely fire/ explosion;
- the extent to which corrosive substances might cause damage to metal/ metal-containing structures (potentially resulting in reduced structural integrity);
- places connected by openings to areas where explosive atmospheres may arise.
If it is identified that an area might have an explosive atmosphere (even for short periods), it must be allocated a ‘zone’, as defined by the regulations.
The DSEAR zones are:
- Zone 0 – A place in which an explosive atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is present continuously, or for long periods or frequently.
- Zone 1 – A place in which an explosive atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is likely to occur in normal operation occasionally.
- Zone 2 – A place in which an explosive atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is not likely to occur in normal operation but, if it does occur, will persist for a short period only.
- Zone 20 – A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is present continuously, or for long periods or frequently.
- Zone 21 – A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is likely to occur in normal operation occasionally.
- Zone 22 – A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is not likely to occur in normal operation but, if it does occur, will persist for a short period only
Entry points into ‘zoned’ areas must be marked with black-edged triangular signs that have yellow backgrounds and are marked with the letters ‘EX’ in black (as described in Schedule 4 of DSEAR). Additional specific requirements may apply, in addition to the above, depending on the area being assessed – your competent person must know and understand these, as well as being able to identify what equipment you are already using within ‘zoned’ areas.
For risk reduction, the regulations set out an order of priority in which mitigation measures, that could prevent the spread of a fire or explosion and reduce the potential number of employees exposed, should be applied.
These measures include:
- reduction in quantity
- control of vapour release
- explosive atmosphere avoidance
- removal of hazardous vapours, gases, dusts, etc.
- control of ignition sources (including static electricity).
If you have a new building, new area or if there is going to be a change in processes or equipment that may result in an explosive atmosphere, then it must be confirmed as being safe by a person competent in the field of explosion protection for your trade. This is referred to as the verification process.
Recommended reading on the Health and Safety Executive (HSE) website:
When considering issues relating to dangerous substances and explosive atmospheres, you may also need to consider the following legislation, in additon to DSEAR:
Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres Regulations
Where explosive atmospheres may occur, equipment (including electrical equipment) and protective systems must be selected on the basis of the requirements of these regulations. With regards to DSEAR, only equipment that meets the following categories, as defined by the Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres Regulations must be used. These categories indicate whether they are suitable for use around certain gases, vapours, mists, and dusts.
- In zone 0 or zone 20, use only category 1 equipment.
- In zone 1 or zone 21, use category 1 or 2 equipment.
- In zone 2 or zone 22, use category 1, 2 or 3 equipment.
Dangerous Substances (Notification and Marking of Sites) Regulations 1990 (NAMOS)
NAMOS sets out notification requirements for hazardous sites where dangerous substances may be present. For example, the Fire and Rescue Service and the relevant enforcing authority (for the purpose of the Health and Safety at Work Act) must be notified about any site with a total quantity of 25 tonnes or more of dangerous substances (as defined) and provided with specified information.
The regulations also include requirements for warning signage and further notification when specified changes take place at the site.