TL;DR – the short answer
Under DSEAR 2002, employers must assess and control the risk of fire and explosion from dangerous substances, including combustible dusts such as flour, sugar, wood and some plastics. The HSE says the most important mitigation measure is keeping buildings clean, because settled dust fuels the far more destructive “secondary” explosion. That means regular cleaning with suitable vacuum systems rather than brushes or compressed air, and not forgetting high-level surfaces.
Dust is easy to overlook. It settles on beams, racking tops, light fittings and ducting where nobody looks, and it builds up slowly. In warehouses, food production units and distribution centres, that build-up can be more than a cleanliness problem. If the dust is combustible, it can turn a small incident into a building-wide explosion.
This guide explains what the law expects, why housekeeping sits at the centre of dust explosion safety, and how to clean dusty sites without making the risk worse.
0.3mm
Layer of flour that can in principle fill a room with an explosible cloud up to 3m high
Source: HSE, HSG103
5mm
Maximum dust deposit that electrical equipment standards assume
Source: HSE, HSG103
40,000
Average annual non-fatal injuries in UK transportation and storage, 2022/23–2024/25
Source: HSE, 2025
The Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR) require employers to control the risks from fire, explosion and similar events caused by dangerous substances at work. HSE’s guide INDG370 sets out what that means in practice: identify the hazards, assess the risks, put controls in place, and plan for accidents and emergencies [2].
“Dangerous substances” covers more than flammable liquids and gases. Many everyday materials become explosive when finely divided and dispersed as a cloud. For the food industry, HSE lists flour, custard powder, instant coffee, sugar, dried milk, potato powder and soup powder as examples of explosible dusts [3].
Plain-English definition: a combustible dust is any fine solid particle that can burn. When enough of it is suspended in air and meets an ignition source, it can ignite so fast that it causes an explosion.
HSE’s guidance on combustible dusts, HSG103, is blunt: “The most important mitigation measure is maintaining the process buildings in a clean condition.” [1]
The reason is the secondary explosion. A small primary event, perhaps inside a machine, a dust extraction unit or a silo, sends a pressure wave through the building. That wave shakes settled dust off every ledge, beam and pipe into the air, and the resulting cloud then ignites. HSE notes that the secondary explosion is generally more destructive than the first [1].
The amount of dust needed is surprisingly small. HSE says that a layer of flour just 0.3mm thick on the floor can, in principle, fill a room with an explosible dust cloud up to 3m above floor level [1]. That’s thinner than a credit card.
HSE breaks the DSEAR risk assessment into five steps [2]:
| Step | What HSE expects | Where cleaning fits |
|---|---|---|
| 1. Identify hazards | Identify dangerous substances, ignition sources and work activities that involve them | Map where dust is produced and where it settles, including high-level areas |
| 2. Assess the risks | Consider how likely a fire or explosion is and how severe it could be | Dust build-up raises both likelihood and severity |
| 3. Control the risks | Remove or substitute the substance where possible; otherwise control and mitigate | Housekeeping is a key mitigation measure |
| 4. Record and implement | If you employ five or more people, record the significant findings | Document cleaning frequencies, methods and responsibilities |
| 5. Review | Keep the assessment up to date, especially after changes | Re-check frequencies when throughput, products or layout change |
Where an explosive atmosphere could occur, DSEAR also requires areas to be classified into zones. For dusts, these are Zone 20, Zone 21 and Zone 22, in order of how often an explosive dust cloud is likely to be present [2]. Equipment used in those zones, including cleaning equipment, must be suitable for the zone.
The wrong cleaning method can create exactly the dust cloud you are trying to prevent. HSE’s guidance is consistent on the following points [1] [3]:
Safe dust housekeeping: the HSE essentials
On most of the sites we visit, floor-level cleaning is fine. The problems are higher up. The usual blind spots are:
Reaching these areas safely needs planning, the right access equipment and trained operatives. A scheduled programme of cleaning at height with powered access means dust doesn’t accumulate unseen between annual shutdowns.
Dust control isn’t only about explosions. Housekeeping also affects slips and trips, fire load and air quality. HSE figures for the transportation and storage sector show an average of 40,000 workers sustaining non-fatal injuries each year between 2022/23 and 2024/25, and 67,000 workers suffering from work-related ill health [4]. A clean, uncluttered warehouse floor, with pallets, shrink-wrap and dust cleared away, supports every part of that picture.
We have cleaned factories, warehouses and manufacturing plants across the Midlands for more than 20 years, from our Telford head office and our Dudley base. Prime Facility Services is owner-managed. Our quality management system holds ISO 9001 and ISO 14001 accreditation (since 2010), and we have been Safecontractor-accredited since 2013. Our staff are checked and audited under ISO, IPAF, Safecontractor and IOSH.
For combustible dust, the work usually falls into these services:
Cleaning of elevated areas, ventilation shafts, gutters and pipework. Our project managers complete a risk assessment before any high-level work starts, and operatives using scissor lifts need IPAF and PASMA training.
Dust and debris removal, plus deep cleaning of large floor areas, shelving and equipment, with digital cleaning audits to evidence the work.
Cleaning programmes for production areas and heavy machinery, tailored to the specific demands of each manufacturing facility.
Cleaning for production floors, lunchrooms, roof lights and storage tanks.
What a dust housekeeping programme can include
Your DSEAR risk assessment stays with you as the duty holder. Our role is to carry out the housekeeping it calls for, safely and on schedule.
Book a high-level dust survey for your site
Phone 0800 566 8894 or request a survey of your racking and roof steelwork to start a housekeeping plan.
Yes. DSEAR covers dangerous substances that can cause fire or explosion, including combustible dusts such as flour, sugar, dried milk and many other fine powders.
It happens when a smaller first explosion shakes settled dust off ledges and surfaces into the air, and that cloud then ignites. HSE says secondary explosions are generally more destructive than the first.
HSE advises against using compressed air lines to dislodge dust deposits, because this creates dust clouds. Vacuum systems are preferred.
No. HSE says not to use domestic vacuum cleaners. Use industrial equipment suitable for the dust and, in classified areas, equipment suitable for the zone.
Areas where explosive dust atmospheres may occur are classified as Zone 20, 21 or 22, in order of how often an explosive dust cloud is likely to be present. Equipment must be suitable for the zone.
There is no fixed legal frequency. It should be set by your DSEAR risk assessment and based on how quickly dust accumulates. HSE notes that electrical standards assume deposits never exceed 5mm.
Yes. A contractor can carry out the high-level and floor cleaning your DSEAR risk assessment requires, at the frequency it sets, while the assessment itself stays with you as the duty holder. Prime Facility Services provides high-level, warehouse and manufacturing cleaning, with a risk assessment before any work at height. Call 0800 566 8894 to arrange a survey.
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