DSEAR Regulations and COSHH: Which Applies

The Short Answer

COSHH deals with what a substance does to the people who breathe it, swallow it or get it on their skin. DSEAR — the Dangerous Substances and Explosive Atmospheres Regulations 2002 — deals with what the same substance does when it catches fire or explodes.

They are not alternatives. A drum of solvent-based paint thinner in your store is almost certainly both a "substance hazardous to health" under COSHH and a "dangerous substance" under DSEAR, and it needs to appear in two assessments that ask completely different questions about it.

The dividing line is written into the two definitions, and it is cleaner than most people expect: COSHH is keyed to the health hazard classes in the CLP Regulation. DSEAR is keyed to the physical hazard classes. Same labelling system, different half of it.

Where the Line Actually Sits

Both regulations define their scope by reference to CLP — the classification and labelling rules that produce the pictograms on the container. They just take different parts of it.

COSHH regulation 2(1) defines a substance hazardous to health as one:

"which meets the criteria for classification as hazardous within any health hazard class as provided for in the CLP Regulation whether or not the substance is classified under that Regulation"

DSEAR regulation 2 defines a dangerous substance as:

"a substance or mixture which meets the criteria for classification as hazardous within any physical hazard class as provided for in the CLP Regulation, whether or not the substance is classified under that Regulation"

(Emphasis added in both.) The rest of each definition then widens the net — COSHH picks up anything with a workplace exposure limit, any biological agent, and dust of any kind present "at a concentration in air equal to or greater than" 10 mg/m³ inhalable or 4 mg/m³ respirable, each measured "as a time-weighted average over an 8-hour period"; DSEAR picks up anything whose "physico-chemical or chemical properties and the way it is used" create a risk, plus any dust that "can form an explosive mixture with air".

Two things in those definitions catch people out.

"Whether or not the substance is classified." Both regimes apply on the criteria, not on the label. A substance nobody has got round to classifying is still in scope if it meets the criteria. So is a process-generated substance that never arrived in a container at all — welding fume, flour dust, wood dust. Our guide to what COSHH actually covers goes through that in more detail on the health side.

Combustible dust is a DSEAR issue, not just a COSHH one. Flour, sugar, wood dust, metal dust and many others are respiratory hazards under COSHH and capable of forming an explosive atmosphere under DSEAR. If you have been treating your dust extraction purely as a health control, DSEAR is the part you have probably not assessed.

One Substance, Two Assessments

Take a 5-litre tin of cellulose thinner in a body shop.

Question	Regime	What it asks
Will the vapour harm the sprayer's lungs or liver?	COSHH	Is exposure prevented, or adequately controlled?
Is there enough vapour in the booth to ignite?	DSEAR	Is an explosive atmosphere likely to form, and are ignition sources controlled?
Can it be swapped for something less harmful?	Both	COSHH reg 7(2) and DSEAR reg 6(2) both put substitution first
Where and how is it stored?	Both	COSHH reg 7(4)(a) and DSEAR reg 6(6) both require safe storage arrangements
Does the store need a hazardous-area zone?	DSEAR only	Only if an explosive atmosphere may occur there
Does the sprayer need health surveillance?	COSHH only	DSEAR has no health surveillance duty

The overlap in the middle rows is real and you should use it. Nothing in either instrument requires you to write the same control measure out twice in two documents. What you cannot do is assume that because you have a COSHH assessment, the fire and explosion risk has been considered — COSHH never asks that question.

What DSEAR Requires That COSHH Does Not

Three duties have no COSHH equivalent.

1. A risk assessment aimed at fire and explosion

DSEAR regulation 5(1) is the trigger:

"Where a dangerous substance is or is liable to be present at the workplace, the employer shall make a suitable and sufficient assessment of the risks to his employees which arise from that substance."

Regulation 5(2) then lists ten things the assessment must consider, and several are questions a COSHH assessment never raises — "the likelihood that an explosive atmosphere will occur and its persistence", "the likelihood that ignition sources, including electrostatic discharges, will be present and become active and effective", "the scale of the anticipated effects of a fire or an explosion", and "any places which are or can be connected via openings to places in which explosive atmospheres may occur".

That last one is the sleeper. A drain, a duct or a gap under a door can carry a flammable vapour from the place you assessed into the place you did not.

2. A priority order for control that starts with quantity

COSHH regulation 7(3) gives you a hierarchy for controlling exposure. DSEAR regulation 6(4) gives a different one, in explicit order of priority, for controlling risk:

"(a) the reduction of the quantity of dangerous substances to a minimum; (b) the avoidance or minimising of the release of a dangerous substance; (c) the control of the release of a dangerous substance at source; (d) the prevention of the formation of an explosive atmosphere, including the application of appropriate ventilation; (e) ensuring that any release of a dangerous substance which may give rise to risk is suitably collected, safely contained, removed to a safe place, or otherwise rendered safe, as appropriate; (f) the avoidance of— (i) ignition sources including electrostatic discharges; and (ii) adverse conditions which could cause dangerous substances to give rise to harmful physical effects; and (g) the segregation of incompatible dangerous substances."

Note where "avoid ignition sources" sits: sixth of seven. The instinct in most workplaces is to start there — no smoking signs, non-sparking tools — but the regulation puts holding less of the stuff first. Reducing a 200-litre bulk store to a 20-litre working stock does more for the risk than any amount of signage, and it is usually cheaper.

Substitution sits above all of this, in regulation 6(2), in the same "by preference" language COSHH uses for the health side. The same logic that drives our COSHH control measures hierarchy applies here — you work down the list, and you record why you stopped where you did.

3. Zoning, where an explosive atmosphere can occur

Regulation 7(1) requires employers to classify places where an explosive atmosphere may occur into hazardous and non-hazardous, and to classify the hazardous ones into zones under Schedule 2. Schedule 3 then sets requirements for equipment used in those zones, and Schedule 4 covers the warning signs at their entry points.

This is the part that sends people to consultants, and often for good reason. But it is worth being clear about the trigger: zoning only applies where an explosive atmosphere may occur in quantities requiring special precautions. A cleaning cupboard holding four litres of flammable product in closed containers is very unlikely to meet that test. A paint-mixing room with open decanting is a different conversation.

Where the Two Regimes Work the Same Way

Three places, and knowing them saves duplicated effort.

Review triggers. DSEAR regulation 5(3) requires the assessment to be "reviewed by the employer regularly so as to keep it up to date", and particularly where "there is reason to suspect that the risk assessment is no longer valid" or there has been a significant change — which is almost word for word the COSHH regulation 6(3) trigger. If you already run a COSHH assessment review cycle, put the DSEAR assessments on the same cycle rather than a separate one.

The five-employee recording gate. This is the one most worth getting right, because it is widely misstated in both directions. DSEAR regulation 5(4) opens:

"Where the employer employs five or more employees, the employer shall record the significant findings of the risk assessment as soon as is practicable after that assessment is made"

COSHH regulation 6(4) uses the same threshold: "Where the employer employs 5 or more employees, he shall record— (a) the significant findings of the risk assessment...".

So under both instruments, every employer must do the assessment; only employers with five or more employees are required to record it. The duty to assess is not conditional on headcount — COSHH regulation 6(1) bars an employer from carrying out the work at all "unless he has— (a) made a suitable and sufficient assessment...". A four-person firm that has assessed nothing has breached the regulation regardless of what it has written down. In practice, writing it down is how you show you did it, which is why the recording threshold is a floor and not a target.

No work before the assessment. DSEAR regulation 5(5) is blunt: "No new work activity involving a dangerous substance shall commence unless— (a) an assessment has been made; and (b) the measures required by these Regulations have been implemented." COSHH regulation 6(1) achieves the same result with different wording. Bringing a new flammable product on site and assessing it next month is the wrong order under both.

Do You Need a DSEAR Assessment? A Short Test

Work through these. Any yes means DSEAR is in scope for that substance or activity.

Does anything you use carry a flame, exploding-bomb, or oxidising pictogram — or a flash point on its safety data sheet?
Do you store, decant or dispense petrol, diesel, LPG, solvents, thinners, adhesives, aerosols or alcohol-based products?
Does any process generate a combustible dust cloud — wood, flour, sugar, grain, metal, plastics?
Do you hold compressed or liquefied flammable gas, including cylinders for welding or catering?
Do you have a process that heats a liquid near or above its flash point?
Do you charge batteries in an enclosed space, or handle anything that off-gasses hydrogen?

If every answer is no, you may genuinely have no dangerous substances — but record that conclusion, because "we considered DSEAR and found nothing in scope" is a defensible position and silence is not. The safety data sheets you already hold for your COSHH assessments are where the evidence lives: section 2 gives the hazard classification, section 9 gives the flash point and explosive limits.

Getting the Paperwork to Line Up

Most SMEs running both regimes end up with the same practical problem: two sets of assessments, driven off one list of substances, drifting apart as products change. The substance list is the thing that has to stay accurate — once it is wrong, both assessments are wrong, and the one you look at least is the one that rots first.

A chemical register that records the hazard classification for each product — health classes and physical classes — is what lets you answer "which of these needs a DSEAR assessment?" in a minute rather than an afternoon of reading safety data sheets.

Which Regulations Apply Where

COSHH 2002 and DSEAR 2002 both extend to England, Wales and Scotland. Northern Ireland has its own instruments — the Control of Substances Hazardous to Health Regulations (Northern Ireland) 2003 and the Dangerous Substances and Explosive Atmospheres Regulations (Northern Ireland) 2003 — which follow the same structure but are enforced by HSENI rather than HSE. If you operate on both sides of the Irish Sea, the duties are equivalent but the citation you should be quoting is not.

Quick Checklist

Every product on the chemical register has its physical hazard classes recorded, not just health classes
Combustible dusts from your processes are on the DSEAR side as well as the COSHH side
A DSEAR risk assessment exists for each dangerous substance or activity
Quantities held have been reviewed against regulation 6(4)(a) — is the bulk store bigger than it needs to be?
Incompatible substances are segregated in storage
Any place where an explosive atmosphere may occur has been classified, or a reasoned conclusion recorded that none does
Significant findings are recorded if you employ five or more people
DSEAR and COSHH assessments share a review cycle rather than running on separate calendars

Keeping One Substance List Behind Both

The failure mode here is not usually ignorance of DSEAR — it is a substance list that only one of the two regimes is reading from, so a new product gets a COSHH assessment and never gets looked at for flammability.

COSHHmate is being built so the register is the single source: every substance carries its classification once, and the assessments hang off it, with review dates that come round automatically rather than depending on somebody's diary. Pricing will be a flat monthly fee with no per-user charges. If keeping two regimes in step off one list would help, join the waitlist.

Sources

This is general guidance based on the published text of the COSHH Regulations 2002 and the Dangerous Substances and Explosive Atmospheres Regulations 2002. Hazardous-area classification in particular is a specialist exercise — where an explosive atmosphere may genuinely occur, have the zoning reviewed by someone competent in explosion protection, as regulation 7(4) itself contemplates. Not legal advice.