Where hazardous dust, fumes, vapours, or mists are generated, controlling employee exposure is both a legal and a practical priority. Under the Control of Substances Hazardous to Health (COSHH) Regulations, employers must assess the risks posed by hazardous substances and implement effective measures to prevent or adequately control exposure.
Workplace Exposure Limits (WELs) are vital as they act as guidelines for evaluating airborne substances, whereas Local Exhaust Ventilation (LEV) is highly efficient when it comes to controlling airborne contaminants through engineering controls. It is important to learn more about the relationship between WELs and LEVs in order to protect workers effectively.
In this guide, we explain what Workplace Exposure Limits are, how they relate to LEV systems, and how DevineAir helps businesses achieve effective exposure control through professional LEV design, consultancy, Thorough Examination and Testing (TExT), maintenance, and awareness training.
Workplace Exposure Limits (WELs) are exposure limits established by HSE, the UK health and safety agency, for various hazardous substances present in the workplace atmosphere. They assist employers in evaluating the level of exposure of the employee to dust, fumes, vapours, or mists. Nevertheless, even when WEL is met, it still does not mean that the employer has complied with COSHH regulations. To be on the safe side, employers should minimise exposure as much as reasonably possible, for example, through proper engineering controls like local exhaust ventilation (LEV).
Workplace Exposure Limits are guidance values published by the Health and Safety Executive (HSE) in EH40 Workplace Exposure Limits. They specify the maximum concentration of certain hazardous substances that workers may be exposed to in workplace air over a defined period.
This is how these limits are applied during a risk assessment to establish if the current controls are providing adequate protection for employees. These limits play a vital role in the COSHH legislation, but they must not be taken as targets. The employer has the responsibility to minimise exposure as much as possible.
It is also important to remember that not every hazardous substance has a Workplace Exposure Limit. Where no WEL exists, employers must still assess the risk and implement suitable control measures to minimise exposure.
Most Workplace Exposure Limits are expressed as either a Long-Term Exposure Limit (LTEL) or a Short-Term Exposure Limit (STEL).
The Long-Term Exposure Limit (LTEL) measures the average concentration of a hazardous substance over an eight-hour working day. It is intended to protect employees from the health effects associated with repeated exposure over months or years.
The Short-Term Exposure Limit (STEL) measures exposure over 15 minutes. It is designed for substances that can cause immediate health effects, such as respiratory irritation or dizziness, following short periods of high exposure.
Understanding these limits helps employers assess workplace risks and determine whether existing controls remain effective.
Many hazardous substances found in workplace air cannot be seen or smelled, yet prolonged exposure can lead to serious health conditions.
Industries such as manufacturing, woodworking, construction, laboratories, food production and chemical processing often generate airborne contaminants that require careful management.
Without effective control measures, exposure can contribute to conditions including:
Preventing exposure is always preferable to treating occupational illness. This is why COSHH requires employers to assess risks, implement suitable control measures and regularly review their effectiveness.
Three key documents underpin workplace exposure control in the UK.
The COSHH Regulations require employers to assess hazardous substances and prevent or adequately control employee exposure.
EH40 Workplace Exposure Limits provides the published exposure limits for many hazardous substances.
HSG258: Controlling Airborne Contaminants at Work provides practical guidance on the design, commissioning, testing and maintenance of Local Exhaust Ventilation systems.
Together, they help employers understand both the legal requirements and the practical steps needed to reduce workplace exposure.
One of the most effective ways to reduce employee exposure to hazardous airborne substances is through Local Exhaust Ventilation (LEV).
Rather than allowing contaminants to spread throughout the workplace, an LEV system captures them as close to the source as possible before they reach employees' breathing zones.
A typical LEV system includes a capture hood, ductwork, an air-cleaning device, a fan, and a safe discharge point. When designed correctly, it significantly reduces airborne contamination and supports compliance with Workplace Exposure Limits.
Not necessarily.
A common misconception is that remaining below a Workplace Exposure Limit automatically means a business has complied with COSHH. In reality, employers must reduce exposure as far as reasonably practicable, not simply stay below a numerical limit.
Effective exposure control should include:
LEV is one of the most important engineering controls, but it works best when combined with good workplace practices.
Installing an LEV system is only the beginning. Over time, filters become blocked, fans lose efficiency, and ductwork can become damaged, reducing the system's ability to control hazardous substances.
Under COSHH, most LEV systems require a Thorough Examination and Test (TExT) at least every 14 months, although some applications require more frequent testing.
Regular maintenance between statutory examinations is equally important. Planned servicing helps identify faults early, maintain airflow, reduce unexpected downtime and extend the lifespan of extraction equipment.
Workplace Exposure Limits provide an important framework for assessing employee exposure to hazardous airborne substances, but effective exposure control requires much more than monitoring air quality. Employers must ensure that suitable engineering controls are in place, maintained correctly and regularly reviewed.
A professionally designed and well-maintained LEV system remains one of the most effective ways to capture hazardous contaminants at the source and protect employee health.
At DevineAir, we provide comprehensive LEV solutions, including design, consultancy, Thorough Examination and Testing, maintenance, awareness training and specialist ventilation services, helping organisations across the UK create safer workplaces and meet their obligations under COSHH. You may also check our website to learn more about the services we offer.
Therefore, in case you are looking forward to installing a new LEV system, your system needs a Thorough Examination and Test or you would like some professional guidance in terms of exposure control in the workplace, feel free to get in touch with DevineAir.
What is a Workplace Exposure Limit (WEL)?
A Workplace Exposure Limit is the maximum concentration of a hazardous substance in workplace air that employers use to assess employee exposure under COSHH.
Does every hazardous substance have a WEL?
No. Some hazardous substances do not have published Workplace Exposure Limits, but employers must still assess the risks and implement suitable controls.
How often should an LEV system be tested?
Most LEV systems require a Thorough Examination and Test at least every 14 months, although some applications require more frequent testing.
What LEV services does DevineAir provide?
DevineAir offers LEV design and consultancy, Thorough Examination and Testing (TExT), maintenance, LEV awareness training, LEV logbooks, fume cupboard testing, MSC testing, KI-Discus testing, and workplace air quality services to help businesses maintain safe and compliant workplaces.
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