The Central Legal Question in COSHH Compliance
Regulation 7 of the Control of Substances Hazardous to Health Regulations 2002 (SI 2002/2677) places an absolute duty on employers to ensure exposure to hazardous substances is either prevented or, where prevention is not reasonably practicable, adequately controlled. The term 'adequate control' sounds straightforward. In practice, it is the source of more HSE enforcement action than almost any other provision in COSHH. This article explains what 'adequate control' legally means, how enclosures are assessed, and where sites most commonly fail.
The Hierarchy: Prevention Before Control
Before reaching the question of whether an enclosure 'adequately controls' exposure, Regulation 7(1) demands that you first ask whether exposure can be prevented entirely. Prevention means:
- Eliminating the substance (substitution with a less hazardous material)
- Changing the process so no hazardous substance is produced or released
- Using the substance in a form that does not create exposure (e.g., pellets instead of powder)
Only when prevention is not reasonably practicable does adequate control become the operative duty. Many COSHH assessments skip this step and proceed directly to ventilation controls — a common enforcement trigger.
What 'Adequate Control' Legally Requires
Regulation 7(7) specifies what constitutes adequate control. For substances with a Workplace Exposure Limit (WEL), exposure must be reduced to below the WEL — not merely to the WEL. The HSE's Approved Code of Practice (ACoP L5) states clearly that achieving the WEL is a floor, not a ceiling. For carcinogens and sensitisers listed in EH40 Table 3, control must be to as low as reasonably practicable (ALARP) below the WEL.
For substances without a WEL, adequate control means applying good occupational hygiene practice — typically demonstrated by reference to published control guidance sheets (HSE COSHH Essentials toolsheets).
The Enclosure Test in Practice
When a 'suitable enclosure' is used as the primary control measure — common in chemical decanting, mixing, and storage operations — it must meet a specific performance standard. The enclosure must:
- Contain the process completely, preventing release to the general atmosphere
- Maintain a negative pressure differential relative to the surrounding workspace
- Be leak-tested and show documented performance (face velocity testing is standard)
- Include a means of safe intervention (glove box, access panels with interlocks)
A polycarbonate splash guard in front of a decanting area is not an enclosure. A ventilated cabinet with 0.5 m/s face velocity across the open face, ducted to atmosphere, may qualify — but only if it is maintained and tested at regular intervals.
Regulatory Reference Table
| Requirement | Regulation / Guidance | Detail |
|---|---|---|
| Adequate control duty | COSHH Reg. 7(1) | Prevent or adequately control exposure |
| WEL compliance | COSHH Reg. 7(7)(a) | Exposure below WEL at all times |
| Carcinogen ALARP | COSHH Reg. 7(7)(b) | As low as reasonably practicable below WEL |
| Enclosure performance | HSE EH40 / ACoP L5 | Documented face velocity, leak testing, maintenance records |
| LEV thorough exam | COSHH Reg. 9 | Every 14 months minimum (Sch. 4 substances more frequent) |
| Monitoring duty | COSHH Reg. 10 | Where enclosure adequacy cannot be determined by inspection alone |
Where Sites Fail the Enclosure Test
The most common enforcement-triggering failures HSE inspectors find during COSHH inspections include:
- No face velocity records — the LEV system has never been tested. Under Regulation 9, thorough examination of LEV must be carried out every 14 months and records kept for 5 years.
- Damaged enclosures in service — cracked seals, missing access panel gaskets, and open ductwork joints all compromise containment performance.
- Inadequate airflow for substance — face velocity of 0.3 m/s may suffice for low-volatility substances but is wholly inadequate for methanol or acetone vapours. The substance's volatility and toxicity must inform the required airflow.
- No monitoring under Regulation 10 — where adequacy cannot be determined by inspection alone (typically for WEL substances with 8-hr TWA below 1 ppm), atmospheric monitoring with calibrated equipment and competent analyst is required.
Secondary Containment as Supplementary Control
Enclosure controls focus on airborne exposure pathways. Liquid containment — bunded pallets, drip trays, secondary containment systems — addresses the liquid spill pathway, which is separately required under COSHH Regulation 7 for substances hazardous by skin absorption or ingestion. The two systems are complementary, not alternative. A site running a correctly specified LEV enclosure but with no secondary liquid containment fails the holistic 'adequate control' test for substances absorbed dermally, such as phenol or aniline.
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