Gas Exposure Limits

Introduction to Gas Exposure Limits

Employers have a legal duty to protect workers from exposure to harmful materials such as dusts, fumes, gases, vapours, mists, biological agents, chemicals, and even emerging risks like nanotechnology, all of which can enter the body through inhalation, skin contact, injection, or ingestion.

In cases where substances are classified as carcinogens, the Control of Substances Hazardous to Health Regulations 2002 (COSHH) require exposure to be reduced to as low as is reasonably practicable (ALARP). Workplace Exposure Limits (WELs) are set by the Health and Safety Executive (HSE) in Great Britain as legally approved occupational limits. These limits define the maximum concentration of a hazardous substance in the air, averaged over a specified time period, and are designed to help control exposure and protect workers’ long-term health.

Gas exposure limits in the UK

Gas exposure limits are found in the ED40 document on the HSE website, see here: EH40.pdf.

The table is found on page 9 and finishes on page 21. the table shows the gas along with the CAS number and the TWA and STELs with any additional comments.

A CAS number is a unique identification number assigned to every chemical substance by the Chemical Abstracts Service. It is like a barcode for chemicals and every gas, vapour, dust or chemical has its own unique CAS number. It removes confusion caused by different names for the same substance.

The TWA and STELs are shown as ppm and mg/m3. TWA is the average concentration of a hazardous substance a worker can be exposed to over a normal working shift (typically 8 hours per day, 40 hours per week). STEL stands for Short-Term Exposure Limit. This is the maximum safe concentration a worker can be exposed to for a short period (15 minutes).

Gas exposure limits in the UK (examples of main gases our customers usually deal with)

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