Storage and use of flammable and explosive substances significantly increase the risks to your employees and your business if a fire occurs. The Dangerous Substances And Explosive Atmospheres Regulations 2002 (DSEAR) define the control measures needed to reduce risks of explosion and fire under these conditions (see Summary Sheet A23).
The regulations apply to dangerous substances, which are defined as:
- explosive, oxidising, extremely or highly flammable;
- ones which create a risk because of physical and/or chemical properties; and
- any dust which can form an explosive mixture with the atmosphere.
You have a duty to ensure that risks from dangerous substances are either eliminated or reduced so far as is reasonably practicable. Where elimination is not possible, you need to take appropriate measures to reduce the risk.
Many of the aspects relating to the identification and proper control of equipment and operating procedures in potentially explosive atmospheres are complex and involved. It is likely that you will require assistance from a competent person to help you complete the necessary risk assessments and put appropriate equipment and procedural controls in place to reduce risks to acceptable levels.
As a guide, the material safety data sheets (MSDS) used in completing COSHH assessments (see hazardous substances) can also help you establish whether the substance is classified as a ‘dangerous substance’ under DSEAR. There should be clear indications in parts 2, 3, 5, 9 and 10 of the standard 16 part format for MSDS.
If you read the words ‘flammable’, ‘highly flammable’, ‘extremely flammable’ or ‘explosive’ on the MSDS for the substance, it is likely to come under the ‘dangerous substance’ definition in DSEAR. The added risks need to be taken into account. You should consider obtaining competent advice before proceeding further.
The five parts of the MSDS listed above, cover the following points:
- Part 2. Composition/information on ingredients
— shows the ingredient name(s) and mixture ratios, where applicable.
Part 3. Identification of hazards — shows an indication of the flammability, where applicable, through the use of adjectives like ‘highly’ or ‘extremely’. If either of these words or equivalents is used, consider the substance to be ‘dangerous’ under DSEAR.
Part 5. Fire fighting measures — shows values for ‘flash point’, ‘flammability class’, ‘lower explosive limit (LEL)’ and ‘upper explosive limit (UEL)’.
The ‘flash point’ is the minimum temperature at which the liquid produces a sufficient concentration of vapour above its surface to form an ignitable mixture with air. The source of ignition could be an open flame or a hot surface.
‘Flammability class’ is usually a written description of this property – e.g. ‘a flammable gas’.
The ‘LEL’ is the lowest volume ratio of a flammable gas or vapour in air which will form an explosive atmosphere. Similarly, the ‘UEL’ is the highest volume ratio of a flammable gas or vapour in air which will form an explosive atmosphere. However, this does not mean that a mixture below the LEL or above the UEL will not explode because there is a danger of dilution or enrichment, depending on the circumstances at the time that could form an explosive concentration.
Part 9. Physical and chemical properties — shows values for the vapour density, vapour pressure, specific gravity (for a liquid), boiling point and other properties as appropriate.
Vapour density is an indicator of the vapour’s weight compared to air. A vapour density above 1 means the substance will sink to the floor whereas below 1 suggests that it will rise to the ceiling. A tendency to sink to the floor could lead to the vapour igniting from a source of ignition remote from the source of the vapour.
However, sinking to the floor or rising to the ceiling is only likely to occur under essentially static conditions. Even a moderate air flow, which is likely when the area is being ventilated (a common means of control), will promote mixing of the substance with air and with some substances could form an explosive mixture.
Part 10. Stability and reactivity — shows which conditions to avoid and lists any incompatible substances.
Conditions to avoid could include, for example, heating of the substance, as this may create an explosion hazard that does not exist at room temperature.
For each dangerous substance, you should:
1. make a suitable and sufficient risk assessment, based on:
- its hazardous properties;
- how it is used (processes, quantities, mixtures, etc.);
- potentially high risk activities;
- existing control measures;
- the likelihood of an explosive atmosphere being formed;
- potential sources of ignition;
- the scale of a fire or explosion, should one occur; and
- the likely effect on adjacent areas should a fire or explosion occur.
2. record the findings and actions needed to ensure that all related workplaces, work equipment and processes are safely designed, operated and maintained at all times. The actions may include:
- reducing the quantity of the dangerous substance;
- preventing or minimising the release of the dangerous substance;
- preventing the formation of an explosive atmosphere (e.g. by effective safe ventilation);
- safe management of any release of the dangerous substance;
- elimination or proper control over any sources of ignition;
- segregating all incompatible dangerous substances; and
- placing an ‘EX’ warning sign at each entrance to a place where an explosive atmosphere may occur.
The distinctive features of an ‘EX’ sign are (a) its triangular shape and (b) black letters on a yellow background with black edging (the yellow part to take up at least 50% of the area of the sign, in line with the requirements of The Health And Safety (Safety Signs And Signals) Regulations 1996.
Where an explosive atmosphere may occur, you should record sufficient information to show:
- the classification of the zone (i.e. the area where an explosive atmosphere may occur). ( see electrical safety );
- the type of equipment needed (e.g. category 1 enclosures certified by accredited authorities for use in zone 0 or zone 20 explosive atmospheres);
- that any claimed verification by a competent person has been completed; and
- how your management system for dangerous substances co-ordinates with related procedures (e.g. permits-to-work etc.).
Further useful information includes: