EH40 Workplace Exposure Limits and Confined-Space Cleaning

Workplace exposure limits are the maximum concentrations of hazardous substances in the air, averaged over a set period, that workers can be exposed to. They are published by HSE in EH40, and COSHH requires that exposure is either prevented or controlled below the relevant limit.

A limit is usually expressed as a long-term average over eight hours and, for some substances, a short-term limit over fifteen minutes. The point of both is the same: to keep exposure below the level where harm becomes likely. A cleaning product whose volatile components have generous limits, and which releases very little vapour at use dilution, is inherently easier to keep within them.

In an open workshop, general ventilation does a lot of the control work for you. A turbine interior removes that safety margin. HSE's confined spaces guidance notes that a space can become confined because of the work being done, and cleaning is a good example: it introduces vapour into a space where air movement is limited and exposure can build.

That is why a solvent-heavy product is a poor fit for turbine interiors even when its individual substances have published limits. Concentrating vapour in a small, still space pushes exposure toward those limits quickly, and the usual response, more ventilation or more respiratory protection, is exactly what is hardest to arrange up a tower. Reducing the vapour at source is the more reliable control.

The hierarchy of control puts substitution above ventilation and PPE for a reason: removing the hazard at source is more reliable than managing it. Choosing a water-based, non-flammable, barely-perceptible-odour cleaner is a substitution-level decision that lowers the exposure you then have to control against EH40, rather than leaning on respiratory protection to bridge the gap.

This is where product data earns its place in the assessment. A safety and compliance profile that shows no substances of very high concern and a low-odour position at use dilution is not marketing detail. It is what makes the exposure limits easy to satisfy. The full assessment logic is set out in the COSHH risk assessment for wind turbine cleaning.

A COSHH assessment that references EH40 should show its working. It should identify the relevant substances, state the exposure limits, explain why exposure at use dilution stays below them, and record the controls that keep it there. Where a product releases very little vapour, that reasoning is short and defensible.

The value of that record is that it survives an audit and a change of crew. It shows the cleaning step was controlled by design, not by hoping the space was ventilated enough on the day. For confined offshore work, that distinction is the difference between a defensible system and a lucky one.