EH40/2005: Workplace Exposure Limits

What is this document?

EH40/2005 Workplace Exposure Limits is the HSE's official publication listing the UK's occupational exposure limits for hazardous substances. It contains the Workplace Exposure Limits (WELs) that apply under the Control of Substances Hazardous to Health Regulations 2002 (COSHH).

This document is essential for anyone conducting COSHH assessments or designing controls for workplaces where employees may be exposed to airborne hazardous substances. It provides the legal limits against which you must measure and control exposure.

EH40 is regularly updated as new scientific evidence emerges and European and international standards change. Always ensure you are using the current edition.

Who needs to read this?

Employers who need to assess exposure to hazardous substances under COSHH
Occupational hygienists conducting exposure monitoring and assessment
Health and safety managers responsible for COSHH compliance
Safety consultants advising clients on hazardous substance controls
Occupational health professionals assessing workplace health risks
Laboratory managers working with chemical substances
Manufacturing and process managers where employees are exposed to dusts, fumes, or vapours

What are Workplace Exposure Limits?

Workplace Exposure Limits (WELs) are British occupational exposure limits set to help protect the health of workers. They represent concentrations of hazardous substances in the air, averaged over a specified time period, that should not be exceeded.

WELs are set at levels that are considered safe for most workers over a working lifetime, though some individuals may be affected at lower concentrations due to individual susceptibility.

Types of WEL

EH40 lists two types of limit for each substance:

Long-term exposure limit (8-hour TWA)

Time-Weighted Average over an 8-hour working day
The maximum average concentration over a standard working shift
Controls daily exposure to substances that may cause harm over time

Short-term exposure limit (15-minute STEL)

The maximum concentration over any 15-minute period
Controls exposure to substances that may cause acute effects
Prevents excessive peak exposures even if the 8-hour average is acceptable

Some substances have only a long-term limit, while others have both. The document indicates which limits apply to each substance.

Key points covered

The legal framework

EH40 explains how WELs fit into COSHH:

Legal status — WELs are maximum concentrations that must not be exceeded
Duties — Employers must ensure exposure is below the WEL and reduced as low as reasonably practicable
Assessment — WELs help you judge whether your controls are adequate
Monitoring — You may need air monitoring to check compliance

Table of WELs

The core of EH40 is the table listing substances and their limits. For each substance, you will find:

Substance name — The chemical or common name
CAS number — The Chemical Abstracts Service registry number for identification
Long-term WEL — The 8-hour TWA limit in mg/m³ and/or ppm
Short-term WEL — The 15-minute STEL where applicable
Notations — Additional information such as skin absorption potential

Notation meanings

Key notations in EH40 include:

Sk (Skin) — The substance can be absorbed through the skin, contributing to overall exposure
Sen (Sensitiser) — The substance may cause respiratory or skin sensitisation
Carc (Carcinogen) — The substance is a known or suspected carcinogen
BMGV — A Biological Monitoring Guidance Value exists for the substance

Substances without WELs

Not all hazardous substances have a WEL. Where no specific limit exists:

You must still control exposure as low as reasonably practicable
You may need to use limits from other sources (manufacturer, international standards)
The principles of good occupational hygiene still apply
Risk assessment must consider all available toxicological information

How to use EH40

Step 1: Identify the substances

List all hazardous substances present in your workplace that could result in airborne exposure. Check safety data sheets for substance identities.

Step 2: Look up the WELs

Find each substance in EH40's alphabetical table. Note:

The 8-hour TWA limit
Any 15-minute STEL
Any notations (Sk, Sen, Carc, etc.)

Step 3: Assess exposure

Determine likely exposure levels through:

Estimation based on the process
Comparison with similar workplaces
Air monitoring and sampling

Step 4: Compare with the WEL

If exposure approaches or exceeds the WEL, you must implement additional controls. Even if exposure is below the WEL, you must still reduce it as low as reasonably practicable.

Step 5: Apply appropriate controls

Use the hierarchy of control:

Eliminate the substance
Substitute with something less hazardous
Enclose the process
Use local exhaust ventilation
Improve general ventilation
Reduce the number of workers exposed
Reduce duration of exposure
Personal protective equipment (as a last resort)

Step 6: Monitor and review

Where exposure could be significant, conduct periodic air monitoring. Review your assessment when processes change, new information emerges, or at regular intervals.

Important principles

WELs are not safe levels

A WEL is not a boundary between safe and unsafe. It represents a level above which exposure must not occur. Employers must still reduce exposure as far below the WEL as reasonably practicable.

Mixtures of substances

When workers are exposed to multiple substances, you cannot simply assume each WEL applies independently. Substances with similar health effects may have additive or synergistic effects. EH40 provides guidance on assessing mixed exposures.

Individual susceptibility

Some workers may be affected at levels below the WEL due to:

Pre-existing health conditions
Individual sensitivity
Previous sensitisation
Pregnancy

Risk assessment should consider vulnerable individuals.

Skin exposure

For substances with the "Sk" notation, airborne monitoring alone is not enough. You must also control skin contact, as significant absorption can occur through the skin.

Updates and amendments

EH40 is updated periodically as:

New scientific evidence becomes available
EU or international standards change
New substances are added
Existing limits are revised

Always check you are using the current edition. The HSE website publishes updates and amendments between full editions.

Relationship with COSHH

EH40 supports COSHH compliance but does not replace the need for proper risk assessment. Under COSHH you must:

Assess the risks — Identify hazardous substances and who may be exposed
Decide on controls — Use EH40 to help determine what exposure levels are acceptable
Implement controls — Put measures in place to keep exposure below WELs
Monitor exposure — Check that controls are working
Health surveillance — Where appropriate, monitor workers' health
Train workers — Ensure employees understand the risks and controls

Common substances covered

EH40 includes limits for hundreds of substances, including:

Solvents — Toluene, xylene, acetone, white spirit
Metals and compounds — Lead, cadmium, chromium, nickel
Dusts — Wood dust, silica, flour dust, general inhalable dust
Gases — Carbon monoxide, nitrogen dioxide, hydrogen sulphide
Fibres — Asbestos (separate regulations), man-made mineral fibres
Biological agents — Some biological substances have guidance values

Workplace Exposure Limits