What are Workplace Exposure Limits (WELs)?
Understanding Workplace Exposure Limits (WELs)
Workplace Exposure Limits (WELs) are limits set by the Health and Safety Executive (HSE) to help protect workers from the harmful effects of hazardous substances in the workplace.
A Workplace Exposure Limit represents the maximum average concentration of a hazardous substance that employees may be exposed to over a specified period, provided that exposure is adequately controlled.
WELs are an important part of the Control of Substances Hazardous to Health (COSHH) Regulations and help employers assess whether their existing control measures, including Local Exhaust Ventilation (LEV) systems, are providing effective protection.
At A-Mac Environmental, we help businesses reduce employee exposure through the design, installation, testing and maintenance of effective LEV systems.
Why are Workplace Exposure Limits Important?
Many industrial processes generate airborne contaminants that can affect employee health if they are inhaled over time.
These contaminants may include:
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Welding fumes
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Wood dust
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Flour dust
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Respirable Crystalline Silica (RCS)
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Metal dust
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Oil mist
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Solvent vapours
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Chemical fumes
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Diesel exhaust emissions
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Laboratory chemicals
Although exposure cannot always be eliminated, it must be adequately controlled to reduce the risk of occupational illness.
Workplace Exposure Limits provide a benchmark for assessing whether control measures are working effectively.
What Do WELs Measure?
Workplace Exposure Limits measure the concentration of hazardous substances in workplace air.
They are usually expressed as:
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Milligrams per cubic metre (mg/m³) for dusts, fumes and mists.
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Parts per million (ppm) for gases and vapours.
These values help employers understand whether employee exposure remains within acceptable limits during normal working activities.
Long-Term and Short-Term Exposure Limits
Many hazardous substances have two different exposure limits.
Long-Term Exposure Limit (LTEL)
The Long-Term Exposure Limit is based on an 8-hour time-weighted average (TWA).
This reflects the average concentration that an employee may be exposed to during a normal working day.
Short-Term Exposure Limit (STEL)
The Short-Term Exposure Limit is based on a 15-minute reference period.
It helps protect workers from brief periods of high exposure that could cause immediate health effects.
Some substances have both long-term and short-term exposure limits, while others may only have one.
How are Workplace Exposure Limits Controlled?
Employers should always aim to prevent exposure where reasonably practicable.
this is not possible, exposure should be controlled using effective engineering controls, including:
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Process enclosure
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Extraction booths
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Dust extraction systems
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General ventilation
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Air filtration
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Safe working practices
Personal Protective Equipment (PPE) should only be used as an additional control measure and not as the primary means of controlling exposure where engineering controls are reasonably practicable.
How LEV Helps Maintain Exposure Below WELs
A properly designed Local Exhaust Ventilation (LEV) system captures hazardous contaminants before they enter the workplace atmosphere.
Effective LEV helps reduce employee exposure to substances including:
Regular inspection, maintenance and Thorough Examination and Test (TExT) help ensure LEV systems continue to perform effectively.
Employer Responsibilities
Under COSHH Regulations, employers must:
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Identify hazardous substances used or generated within the workplace.
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Assess the risks to employees.
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Prevent or adequately control exposure.
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Maintain engineering controls such as LEV systems.
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Monitor exposure where necessary.
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Ensure employees receive appropriate information, instruction and training.
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Carry out regular LEV examinations and testing where required.
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Maintaining exposure below the Workplace Exposure Limit is an important part of protecting employee health.
Industries Where WELs Are Important
Workplace Exposure Limits apply across many industries, including:
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Film and television production
Where hazardous airborne substances are generated, WELs should be considered as part of your COSHH risk assessment.
How A-Mac Environmental Can Help
A-Mac Environmental provides complete LEV solutions to help businesses control airborne contaminants and support compliance with COSHH.
Our services include:
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LEV system design
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Supply and installation
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Airflow performance testing
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Thorough Examination and Test (TExT)
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Planned preventative maintenance
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LEV servicing
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Repairs and upgrades
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Compliance support
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Our experienced P601 and P602 engineers work with businesses throughout Scotland to improve workplace air quality and help maintain effective exposure control.
Frequently Asked Questions
Are Workplace Exposure Limits legal limits?
Workplace Exposure Limits are published by the Health and Safety Executive and are referenced within COSHH guidance. Employers must ensure exposure is adequately controlled, and WELs provide an important benchmark when assessing whether existing control measures are effective.
Does every hazardous substance have a Workplace Exposure Limit?
No. Many substances have published WELs, but not all hazardous substances have a specific exposure limit. Employers must still assess and adequately control any risks associated with hazardous substances, even where no WEL exists.
How can I reduce employee exposure?
The most effective methods include eliminating the hazard where possible, using enclosed processes, installing suitable Local Exhaust Ventilation (LEV), maintaining equipment correctly and following safe working practices.
Does LEV guarantee compliance with Workplace Exposure Limits?
A well-designed and properly maintained LEV system is one of the most effective engineering controls available. However, it should form part of an overall COSHH strategy that includes risk assessment, maintenance, employee training and regular monitoring where appropriate.
If your business generates hazardous dusts, fumes, vapours or airborne particles, A-Mac Environmental can help you design and maintain effective LEV systems that improve workplace air quality and support compliance with COSHH.
Contact our experienced team today to discuss your ventilation requirements or arrange a professional LEV assessment.