What is DSEAR?

Essentially DSEAR ATEX (2002), also known as Statutory Instrument 2002, No. 2776, is the system by which we differentiate and identify Dangerous Substances (the “DS” portion of the acronym), and their risks. It is enforced under the Health and Safety Executive (HSE), as well as local authorities, and is designed to ensure the safety of workers that must work in such conditions.

DSEAR has always included flammable liquids, oils, and dust or particulates which can form additional threats, notably Explosive Atmospheres (the “EA” portion of the acronym). Therefore, together, we get the Dangerous Substances and Explosive Atmospheres Regulations, or DSEAR. Since 2015, included among the requirements are pressurized gases and substances which are corrosive to metal.

Who is Affected by DSEAR?

Fire and Explosion Regulations affect everybody, but DSEAR applies in particular to workplaces in the United Kingdom. It is up to employers, or self-employed individuals, to take stock of all dangerous substances on their premises which could prove to be a threat to themselves, their employees, visitors to the workplace, and to members of the public.

It is then their responsibility to reduce or eliminate risk as far as is practically possible, and to continue to manage risks under the Management of Health and Safety at Work Regulations (1999) aka, Statutory Instrument 1999, No. 3242.

What Is an Explosive Atmosphere?

DSEAR defines explosive atmospheres as a mixture of gases, vapors, mists, or dust of dangerous substances with common air, under ordinary atmospheric conditions, which upon ignition can move from a trivial starting point to combust the entire unburnt mixture.

A trivial starting point may be an ignition source such as an open flame, hot work or surfaces, spark (flint & steel), electric arc (welding, unprotected switches, electric saws & drills), or static-electric discharge. Such “ordinary atmospheric conditions” prevail between -20 to 40º Celsius, and at pressures from 80-110 kPa.

Overlooked Dangers

Let’s consider static electricity for a moment, since it is the lowest energy form mentioned, and which consequently may not be sufficiently regarded as being dangerous. A person shuffling their shoes across a carpet can create a static arc of 10,000 volts at 10-25 millijoules (mJ), dependent upon local humidity.

Grounding an automobile that has just stopped could provide a 500 mJ discharge due to air friction stripping away electrons and building a positive net charge. Notably, an arc must be 1 mJ in order for you to feel it, and 50 mJ can make you flinch. 500 mJ could probably make you exclaim aloud.

It would take 1,350 mJ to kill a person, so ordinary human body static is less than 2% of a lethal amount. However, it only takes a 17 mJ arc to ignite fine wood dust in a sufficiently densely loaded atmosphere (70 grams/m3). You could not, for example, ignite coal dust which such a discharge, which would require 110 mJ of energy. Insulated machines, however, can achieve much higher levels of electrostatic loading.

Dust removal systems, particularly those made of non-conductive materials, such as Black Alkathene (MDPE), PVC, or ABS, will almost invariably have a conductor wire inside which is grounded. Someone undertaking a repair that is uninitiated in this fact may cut the wire during repairs and not reattach it upon completion. This can create an explosion hazard in a previously “safe” system, thus, ordinary static electricity is not to be taken lightly.


Depending on the composition of the atmosphere, the speed of propagation can change. Small particles (e.g. powdered sugar, flour) have less “fuel” per particle, but a much higher surface area for their volume. This means increased exposure to the oxygen in the air, lending them to much faster combustion speeds.

Also due to their smaller size, they can be more densely associated, and can “cascade” rapidly. As each particle ignites and releases energy, it triggers numerous neighbours, and the energy level can rapidly escalate.

This is used for good purpose in special effects (SFX) for films, where what may appear to be gasoline/petrol explosions of vehicles, are often created with dust clouds that have been ignited. These explosions rise in a magnificent fireball and, because of the limited amount of fuel, are self-extinguishing, thus being safer for movie-making purposes.

Types of Explosions

Explosions as a generic term can be further broken down into detonations and deflagrations. Gaseous mixtures of air and a pressurised gas such as propane or natural gas (methane), or suspended particulates such as flour, sugar, and sawdust can explode in, either way, depending on existing conditions.

If the mixture detonates, it will propagate through the atmosphere faster than the speed of sound. This is not a heat-derived expansion—it is instead a rapid chemical reaction. This generates a (frequently destructive) pressure front or shock wave before it due to the supersonic expansion.

If the fuel deflagrates, its effect will propagate more slowly than the speed of sound and the primary effect is heat at the wavefront. Make no mistake—both are equally threatening in the wrong circumstances. You can hear & see the difference in the linked YouTube video.

What is a DSEAR assessment?

DSEAR assessments are a formal requirement for all employers that have or use materials classified with the properties of being capable of posing an explosion hazard, similar energy-releasing events, or of corroding metal. The need for an inspection can be triggered by a normal fire inspection with your safety officer.

If a risk is deemed to exist, the DSEAR assessment is required. This assessment must:

  • Identify dangerous materials (e.g. solvents, aerosolized paints, flammable gases);
  • Implement measures (e.g. cleaning policies) to mitigate or control risks;
  • Provide control measures to reduce the effects of an incident if it does take place;
  • Have procedures to deal with resultant incidents, accidents, or emergencies;
  • Inform and train employees to safely manage any risks from dangerous substances;
  • Identify areas where explosive atmosphere risk may exist or occur; and
  • Avoid ignition sources (sparks, flames, hot surfaces, etc.) in any risk areas.

DSEAR Regulations

DSEAR is a set of regulations that also encompasses the ACOP (Approved Codes of Practice), used to assist in complying with the DSEAR regulations. Those regulations include:

  • DSEAR itself;
  • ATEX regulations from the E.U.;
  • Proper petroleum handling;
  • Fire Safety in the Workplace;
  • Pressurised Gases & metal-corrosive substances; and
  • Celluloid.


DSEAR implements the parameters of ATEX, taken from the French Atmosphère Explosibles regulations that apply throughout the E.U. These are concerned with vapors, mists, flammable gases, and dust that can form explosive atmospheres. Using these guidelines, DSEAR ATEX requires that any workplace containing these hazards be classified into Zones, based on the level of threat that exists, and the risk of such an explosion taking place.

These zones are defined as “any place in which an explosive atmosphere may occur in quantities such as to require special precautions to protect the safety of workers”. Such zones must be secured by utilizing protective systems and equipment which comply with the categories described in the Equipment and Protective Systems (EPS), for Use in Potentially Explosive Atmospheres Regulations.


Petrol/gasoline is an always dangerous, explosive, and flammable substance. It can give off explosive vapours even at very low temperatures. If it did not do so, it would be considerably less useful as a fuel for automobiles.
Consequently, however, this product always presents a source of ignition which can rapidly cause fire, personal injury, and loss of life. Locations that store and dispense this fuel in a workplace are thus covered under DSEAR, as well as additional regulations regarding permissible containers.


DSEAR and diesel fuel is a contentious issue with regards to ATEX-rated equipment for dispensing and storage. Both suppliers and installers must ascertain that a hazardous condition does not exist and that diesel cannot be introduced to a source of ignition. Auto-ignition temperature for diesel lies between 220-285º Celsius, well beyond the normal environment.

Mists, however, are much more vulnerable to ignition at lower temperatures and volumes. Mists are formed by leaks at joints/flanges. Proper construction eliminates these. Nearby motors and pumps protected to IP-54 standards (dirt, dust, oil, and non-corrosive material proof) resolve that difficulty. Strictly speaking, DSEAR ATEX certification is probably not required, but for a trivial cost it shows industrial responsibility to the community and builds faith in corporate responsibility for the public—it’s a good investment.

Fire Safety

Fires, unfortunately, occur by the thousands per year in commercial premises. The main responsibility for the HSE is for special precautions to reduce the probability that a fire will break out in the first place or, if it does occur, to lessen its intensity.

Responsibilities for oversight include:

  • the storage of flammable liquids in working areas, such as laboratories, workrooms, or in the process area itself;
  • selecting equipment such that it will not provide a source of ignition;
  • atmospheric extraction systems to remove combustibles;
  • containment/capture systems for airborne paints and solvents; and
  • ventilation systems to remove gases and vapors.

Pressurised Gases

Gases in cylinders can present an explosion hazard if not managed properly. They can be subject to:

  • Connexion leaks of flammable gases;
  • Physical damage from tipping or collision;
  • Valve failure;
  • Structural containment failure through corrosion.

Proper instruction in the use of dangerous gases is paramount. Fittings must be properly tightened, sealed, and checked for leaks. Cylinders must be chained, or confined in a stable transport mechanism designed for the cylinders being used. Valves should be protected from impacts that could damage or shear them, and tanks should be stored away from standing water, or corrosive substances that could compromise their structural integrity.

Since 2015, DSEAR requires employers to put measures in place to safeguard against these eventualities. In general, if you are already following the requirements of the Health and Safety at Work Act (1974) and the Management of Health and Safety at Work Regulations (1999) you are already in compliance and need not expend additional effort.


Until old film stock is successfully transferred, including early X-rays, to a safer medium (e.g. digital storage), cellulose nitrate represents a significant hazard. It ignites easily and is very difficult to extinguish. This caution applies primarily to archival institutions or anyone in contact with these antedated materials.

What is the difference between DSEAR and ATEX?

Simply put, DSEAR is for the assessment of the substances which can pose fire or explosion risks to people and property, or health and safety risks, to employees. It is designed to oblige employers to be aware of the materials they have at hand and avoid unnecessary risks.

ATEX, on the other hand, provides guidance to help you determine which equipment is appropriate for protective purposes in each Zone which it defines based on its threat level. DSEAR ATEX protocols cannot really be properly accomplished without having completed a DSEAR ATEX examination. You need to know what materials and risks exist before you can move to mitigate or ameliorate them.

Which dangerous substances does DSEAR apply to?

DSEAR incorporates two E.U. Directives: the Chemical Agents Directive (98/24/EC), and the Explosive Atmospheres Directive (99/92/EC). It, therefore, applies to flammable gases (e.g. Liquid Propane Gas, hydrogen, acetylene, carbonyl sulfide), airborne particulate (dust of coal, wood, grain, sugar), powders used as fillers in pharmaceutical preparations, hydrocarbon gases, or liquid fuels (methane, ethane, petrol, oils) and virtually anything else which can pose a fire or explosion hazard in a workplace.

Indeed, while formerly exempt, mining now falls under the umbrella of DSEAR ATEX. It now joins industrial and commercial premises, land-based and offshore installations, quarries, construction sites, vehicles, and vessels.

The Takeaway

It is never a question of DSEAR vs. ATEX because they are designed to do two different things. Ultimately, both are designed to protect people and property but they use complementary pathways to reach that goal.
Risk assessments should only be carried out by competent individuals armed with the essential knowledge, expertise, and familiarity to identify the potential for fire and the generation of explosive atmospheres.
If you have an incident where it is determined that a DSEAR ATEX assessment ought to have taken place, yet did not, this can indemnify your insurance provider, and severely limit your ability to collect for damages. You should never skimp on safety. It is for your own good.