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The Dangerous Substances & Explosive Atmospheres Regulations


The Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR) is the primary legislation applying to the control of substances that can cause fires and explosions in the workplace.

Under the Regulations, a dangerous substance includes any substance or preparation, which due to its properties or the way it is used, could form an explosive atmosphere and so cause harm to people from fires and explosions.  Dangerous substances, in varying quantities, will commonly be encountered in many workplaces in the form of flammable liquids, gases, explosive dusts, etc. and, as such, require close attention by all Consultants.

To further determine the presence of dangerous substances which fall under the scope of DSEAR, reference would have been made as to whether the substances had been classified under the Chemicals (Hazard Information and Packaging for Supply) Regulations 2002 (CHIP).

For the purposes of CHIP, flammable liquids were classified as follows:

  • Flammable Liquid – flash point of >21⁰<55⁰C

  • Highly Flammable Liquid – flash point <21⁰C

  • Extremely Flammable Liquid – flash point<0⁰C and a boiling point of 35⁰C.

With effect from 1 June 2015, the CHIP Regulations were replaced by European Regulation (EC) No 1272/2008: Classification, labelling, and packaging of substances and mixtures (known as the CLP Regulations) in which flammable liquids are now categorised as below:


of Category

CLP Regulations


Category 1:

Flash point < 23°C and initial boiling point ≤ 35°C


Category 2:

Flash point < 23°C and initial boiling point > 35°C


Category 3:

Flash point ≥ 23°C and ≤ 60°C


Under DSEAR, employers are required to:

  • Carry out a risk assessment of any work activities involving dangerous 


  • Provide measures to eliminate or reduce risks of fire and explosion as far as

    is reasonably practicable.

  • Provide controls to reduce the effects of any incidents involving dangerous


  • Prepare plans and procedures to deal with accidents, incidents and

    emergencies involving dangerous substances.

  • Provide employees with information and training.

  • Identify and classify areas of the workplace where explosive atmospheres may occur and avoid ignition sources, including, for example, from unprotected electrical equipment. Areas are to be classified into Zones as defined in Schedule 2 of DSEAR in which equipment and protective systems are to be installed on the basis of the requirements of the Equipment and Protective Systems for Use in Potentially Explosive Atmosphere Regulations 1996 (EPS), thereby fulfilling the ATEX Directives (Technical Bulletin 23 refers).

    As far as this particular aspect is concerned, DSEAR defines places where explosive atmospheres may occur as; a place in which an explosive atmosphere may occur in such quantities as to require special precautions to protect the health and safety of the workers concerned is deemed to be hazardous within the meaning of these Regulations. Consequently, a minor isolated solvent spillage, cleaned up in the normal manner, is unlikely to cause harm and may be disregarded. 

Where there are five or more employees the significant findings of the risk assessment must be recorded in writing, which should include the following:

  • Measures taken to eliminate risk.

  • Sufficient information to show that the workplace and work equipment will be safe from risk of fire and explosion during operation and maintenance.

  • Details of any areas zoned as hazardous due to the likely presence of explosive atmospheres.

  • Where employers share a workplace, any measures to ensure coordination of safety requirements to protect workers from explosive atmospheres.

Such risk assessments will vary in their complexity ranging, for example, from a fairly simple document covering a single oxy-acetylene welding set in a metal fabrication shop to, for instance, more complex assessments where large amounts of flammable liquids are encountered in production processes and in storage.

Before a workplace containing areas classified as hazardous in pursuant to zoning is used for the first time, DSEAR requires that the employer shall ensure that its overall explosion safety is verified by a person who is competent in the field of explosion protection. With the exception of major chemical or other sites where such skills are likely to be available in house, in most cases this will involve the services of a specialist safety consultant. In this respect, it is important to recognise that the specialism required will only be possessed by a small percentage of practicing Fire Safety Consultants.

DSEAR also requires that where employees work in zoned areas, they are provided with appropriate clothing which does not create an electrostatic discharge, and that the hazards of static electricity, generally, forms part of the risk assessment.

Despite having been introduced on 2002, it is reliably stated that some companies, particularly those in the SME sector, continue to have sparse knowledge or awareness of their duties under DSEAR or, if they do, struggle in respect of its application.

Companies providing consultancy services in DSEAR & ATEX matters include:

SGS Baseefa Ltd –

Sira Consulting Ltd –

SDA Technical Services Ltd –

ATEX Explosion Hazards Ltd - 


Practical advice on how to comply with DSEAR is provided by the Approved Code of Practice (ACOP) L138, published by the HSE. ACOPs describe preferred or recommended methods that can be used (or standards to be met) to comply with regulations and the duties imposed by the Health and Safety at Work etc Act. Each ACOP has been approved by the HSE, with consent of the Secretary of State and has a special legal status. If prosecuted for a breach in health and safety law, and it proved that the defendant(s) did not follow the relevant provisions of the Code, a Court will find the defendant(s) at fault unless it can be shown that the law has been complied with in some other way.

Dealing with the storage of flammable liquids in process areas, workrooms, laboratories and similar working areas, the key provisions of the Code are summarised in the following paragraphs.

1. Many work activities will require the convenient availability of flammable liquids and/or flammable liquid-based products. To facilitate this, a limited quantity in suitable closed vessels may be stored in suitable cabinets or bins of fire-resisting construction and which are designed to retain spills (capacity should be 110% volume of the largest vessel normally stored in it).

2. These should be located in designated well-ventilated areas that are:

  • Away from the immediate processing area where possible; and

  • Do not jeopardise the means of escape from process and other areas.

3. The flammable liquids should be stored separately from other dangerous substances that may increase the risk of fire or compromise the integrity of the container or cabinet/bin, such as energetic substances, oxidizers and corrosive materials. Sometimes these other dangerous substances may be flammable liquids in their own right or held in a flammable liquid. However, it is still inappropriate to store these in the same cabinets or bins with other flammable liquids.

4. The recommended maximum quantities that may be stored in cabinets and bins are as follows:

  • No more than 50 litres for extremely or highly flammable liquids (CLP Categories 1 & 2) and those flammable liquids with a flashpoint below the maximum ambient temperature of the workroom/working area;

  • No more than 250 litres for other flammable liquids with a higher flashpoint of up to 60 °C. (CLP Category 3).

5.  These quantities are intended to be viewed as recommended maxima representing industry safe practice, rather than absolute limits. There is some flexibility, where for example the design of modern buildings and the pattern of work can make it difficult to work within these limits, e.g. in large or open-plan workrooms/ working areas. Where the employer proposes to store quantities in excess of the recommended maxima, a robust justification should be recorded, and the risk assessment should take into account:

  • The properties of the materials to be stored or handled in the process areas, workrooms, laboratories and similar working areas (for mixed storage the worst-case situation should be applied, i.e. all materials in the storage cupboard or bin should be considered as being the same material as the one that has the lowest flashpoint).

  • The size of the process area etc and the number of people working in it.

  • The amount of flammable liquids being handled in the process area etc and the quantities of liquid that may be accidentally released or spilled.

  • Ignition sources in the process area etc and potential fire spread in the event of an ignition.

  • Exhaust ventilation provision to the process area etc and/or the storage cupboard or bin.

  • The fire-resisting performance of the storage cupboard or bin.

  • The arrangements for closing the cupboard or bin doors/lid in the event of a fire.

  • Means of escape from the process area etc.

6. The objective, in the event of an incident, is to ensure that people can safely escape from process and other areas. The purpose of storing dangerous substances in cupboards and bins of appropriate construction and design is to provide a physical barrier to defer their involvement in a fire. If the dangerous substances become involved, limiting the passage of fire and hot gas should allow sufficient time for safe evacuation and for the implementation of the employer’s immediate emergency procedures.

7. The ACOP provides general guidance and details of the performance requirements for fire-resisting cupboards and bins. It is important to recognise that these do not specify an absolute test or standard for the cupboard or bin itself, rather they relate to nominal construction principles that are capable of providing the required fire safety performance. Namely that:

  • Materials used to form the sides, top, bottom, door(s) and lid are capable of providing the required fire resistance (i.e. 30 minutes integrity) and reaction to fire (i.e. minimal risk).

  • Joints between the sides, top and bottom of cupboards and bins should be free from openings or gaps.

  • Lid/doors should be close fitting against the frame of the bin/cupboard, such that there is a nominal overlap between the frame and lid/doors in their closed position, and supports and fastenings should be of a material with a melting point greater than 750°C.

The above criteria represent the minimum performance requirements for compliance with the current legislation. It is important that cupboards and bins are fit for purpose; a redundant filing cabinet, for example, may not meet the requirements of the Code.

It is to be noted that there are a number of more demanding standards and design specifications, which refer to the fire performance of the complete cabinet structure, including: BS EN 14470-1: Fire safety storage cabinets – Part 1: Safety storage cabinets for flammable liquids, and Factory Mutual, Underwriters Laboratories and ANSI/NFPA 30 standards. Where standards go beyond the minimum requirements of UK health and safety legislation, it is to be emphasized that their implementation in the UK is not a legal requirement. However, for quantities in excess of the recommended maxima, employers/dutyholders may find cabinets with enhanced fire performance of benefit in making their risk assessment demonstration, together with supporting property and business protection objectives. It is of importance that the use of cabinets with enhanced fire performance should not be seen as a substitute for the provision of dedicated store rooms and outdoor storage areas for the safe keeping of containers which are nominally empty or are not required for current work

As a supplement to the ACOP, further detailed guidance in connection with the fire and explosion hazards associated with flammable liquids storage can be found in HSE HSG51: Storage of flammable liquids in containers -

Typical flammables storage cabinets, many of which are marketed as HSG51 compliant for which a nominal 30 minutes fire resistance (integrity) is inferred, based on their quality steel construction with spot welded seams, gas welded corner joints and a reinforced vertical panel to the door to prevent initial heat distortion.

Typical fire safety storage cabinets designed and tested to BS EN 14470-1, with 30 and 90 minutes fire resistance ratings.


The particular guidance in the ACOP (L138) is replicated below.

  1. In general, gas cylinders and cartridges should be kept below 50°C as there is an increased risk of over-pressurisation and gas discharge or rupture in the event of them being subject to elevated temperatures. For example, this is a risk in the event of a fire in a building containing gas cylinders, even if the cylinders are remote from the source of the fire. The employer should therefore minimise the number of gas cylinders kept indoors. Further guidance on this is below.

  2. Ordinarily gas cylinders containing dangerous substances should not be kept in process areas etc. An exception is for gas cylinders connected to portable appliances, but the number should be limited to the minimum necessary for operational requirements. Where the appliance is fixed, the gas cylinders should normally be sited in a safe location outdoors and the gas piped indoors to the appliance. Gas cylinders that are not in use (i.e. not connected to an appliance) should be stored in safe, secure uncongested locations in the open air that provide ready dispersal of any released gas, and prevent accumulations or entry of gas into any enclosed area. Nominally empty cylinders should also be stored in safe location outdoors to separate them from gas cylinders in use (i.e. connected to an appliance).

  3. Exceptionally, gas cylinders may be stored indoors where there is a specific safety, security or process quality consideration. For example, for toxic or ultra-high-purity gases needed in the electronics industry, where gases have to be temperature controlled for process reasons, or where there is potential risk of deterioration/corrosion of the cylinder/cartridge, then the gas cylinders may be stored indoors. The amounts kept should be minimised and the gas cylinders should be housed/stored in a dedicated, well-ventilated, secure storeroom or cabinet/cupboard of adequate fire-resisting construction.

  4. Where the number of gas cylinders required indoors is so few that a dedicated storeroom is not justified, a dedicated cabinet/cupboard of adequate fire-resisting construction (nominally 30 minutes integrity as previously detailed) should be used. The same storeroom/cabinet/cupboard should not be used for both stored gas cylinders and those nominally in use (connected to an appliance). Nor should it be used to store other incompatible substances or materials that pose a risk to the cylinders.

  5. Further advice on the storage and keeping for use of gas cylinders and cartridges should be available from the supplier or the relevant trade association, such as the British Compressed Gas Association and UKLPG. Information on the location of such cylinders should be given to attending emergency services at the earliest appropriate opportunity.

  6. The employer should justify the need to house/store gas cylinders and cartridges indoors and ensure that any storeroom, cabinet or cupboard provided for the purpose meets the minimum legal requirements.

  7. A number of cabinets are commercially available that meet more demanding standards and design specifications, e.g. BS EN 14470-2: Fire safety storage cabinets - Safety storage cabinets for pressurised gas cylinders, and Factory Mutual, Underwriters Laboratories and ANSI/NFPA 30 standards. Where standards go beyond the minimum requirements of UK health and safety legislation, it is to be emphasised that their implementation in the UK is not a legal requirement, nor should the use of such cabinets be seen as a substitute for siting gas cylinders in a safe location outdoors where it is reasonably practicable to do so.

A typical gas cylinder storage cabinet designed and tested to BS EN 14470-2, rated at 90 minutes fire resistance. 


From June 2015, DSEAR has also covered substances that are corrosive to metals and gases under pressure. It places a formal requirement on employers to assess the risks for substances if classified for these properties and put in place suitable control and mitigation measures.

It is anticipated that the impact of these changes will be minimal because the intrinsic hazards of the substances being used or present in workplaces is unchanged. The need to carry out a risk assessment, and have in place procedures for the safe use of chemicals not previously covered by DSEAR, is already necessary to meet the general requirements of the HSW Act 1974, and the Management of Health and Safety at Work Regulations 1999.

Businesses already complying with these duties are therefore unlikely to need to take any additional action.



In all cases where dangerous substances are used or stored, Consultants are required to enquire as to whether a DSEAR risk assessment has been completed. Where this has been accomplished, perusal of the written assessment should be made, with particular regard to the findings in the assessment and its relationship to the overall conditions prevailing at the time of survey.

In the event that no such risk assessment has been undertaken, an appropriate risk improvement should be raised, where applicable employing the standard RiskSTOP wording.

Where pertinent, the wording may be extended to include reference to specific hazards or adverse features which the Consultant considers should be addressed.

The fact that a DSEAR risk assessment has been carried out and properly documented should not preclude the submission of specific risk improvements, in cases where the risk assessment and/or the risk control measures are deemed by the Consultant to be less than adequate.

Close attention should be given to the internal storage arrangements for flammable liquids as regards both the quantities and flashpoints of the materials observed, and the suitability and condition of storage cabinets employed, with reference to the guidance in the ACOP. Where inadequate arrangements are encountered, the appropriate risk improvements are to be raised.



A number of DSEAR related guidance documents are published by the HSE, many of which are available on free download, including L138: Dangerous Substances and Explosive Atmospheres – Approved Code of Practice and guidance -

HSG140: Safe use and handling of flammable liquids.

HSG176: Storage of flammable liquids in tanks.

The consultancy company websites mentioned in this TB are also examples of sources of information.

This Technical Bulletin should be cross-referenced with TBs 23 (ATEX), 24 (Flammable Liquids), 34 (Industrial Gases in Cylinders) and 62 (The Dangerous Substances (Notification and Marking of Sites) Regulations).

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