Workplace Exposure Limits Explained

Workplace exposure limits (WELS) are legal limits set under COSHH Regulations in order to help protect the health of workers from hazardous substances in the air.

Almost all industries within the UK are regulated by the Health and Safety Executive (HSE).

In this article we will outline what workplace exposure limits are, what determines them, how WELs are calculated, current regulations, and how workplace exposure monitoring can be used in order to quantify, control and reduce exposure to any potentially harmful substances in the air.


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What Are Workplace Exposure Limits?

Workplace exposure limits are specifically used to help protect people from hazardous substances, such as chemicals, gases, dusts, Isocyanates, solvents, vapours and Welding Fumes to name a few.

They are especially important as some substance’s effects on health may not appear until many years after exposure.  

In 2018, the HSE released revised Indicative Occupational Exposure Limit Values (IOELVs) in order to aid the protection of workers exposed to a list of 31 potential workplace hazardous substances.

In order to meet regulation and maintain COSHH Compliance, employers are required to ensure no employees, clients, contractors or members of the public are exposed, by inhalation, contact or absorption to a concentration of any substance in excess of the Occupational Exposure Limits for that specific substance.

If the hazardous substance cannot be completely removed or changed, the level of exposure must be reduced to as low as reasonably practicable (ALARP).


What Is A WEL?  

A WEL is the collective name given to IOELVs in the UK, they are the maximum concentration of a hazardous substance in the air that people breathe, averaged over a specific period of time, referred to as a time weighted average (TWA). Typically, this is eight hours, but short-term exposure periods of 15 minutes are also assigned limit values. 

The HSE defines exposure limit values as the limit of the time-weighted average of the concentration of a chemical agent in the air within the breathing zone of a worker over a specified reference period.”

COSHH Regulations apply to substances that can harm through either skin contact, inhalation, injection, ingestion and contact with eyes.  

WELs specifically apply to exposure by inhalation, as for most substances, this is usually the main route of entry into the body.  

You can usually find resource and information about relevant workplace exposure limits via a substance’s / product’s Materials Safety Data Sheets (MSDS). MSDS contain technical information such as the composition of the chemical, first-aid measures, handling and storage information and disposal considerations for example.  


What Are The Current COSHH Regulations?

The HSE set out the COSHH regulations in the UK for workplace exposure limits via the Control of Substances Hazardous to Health (COSHH) Regulations 2002.

The current UK COSHH Regulations require employers to:

  • Assess the risks that arise from the use of hazardous substances. (COSHH Risk Assessments should include arrangements to deal with accidents, incidents or emergencies and health and safety risks associated with the handling, storage, or disposal of substances)
  • Prevent exposure to potential hazardous substances
  • Control exposure to such substances if prevention is not reasonably practicable
  • Inform, Instruct and Train employees about the risks, steps and precautions that have been taken to control exposure (The provision of PPE etc)

It is the responsibility of the employer to always ensure all health and safety risks are identified and remedied within the workplace under the Health and Safety at Work Act 1974 to safeguard all employees.

Employers should create assessment criteria and working procedures to regulate all exposure to hazardous substances in the workplace and ensure all work spaces are also suitable, well maintained and safe.

Employers should also make sure employee exposure is monitored and controlled with additional ongoing monitoring of employee health via surveillance reports.


What Determines the Workplace Exposure Limits?  

A level where no adverse effects on human health would be expected to occur based on the known and/or predicted effects of the substance.  


A Level corresponding to what is considered to represent good control, accounting for the severity of the likely health hazards and the cost and effectiveness of control solutions.  


How Are WELs Calculated?

There are two time periods when calculating exposure for comparison with WELs: 

Short Term Exposure Limits (STELs)  

  • Usually, 15 minutes to control effects that may be seen after a brief exposure  
  • The STEL exposure limit relates to peak exposure incidents and is designed to protect against immediate acute ill-health effects.  
  • Measures can often be put in place to prevent or to reduce the strength and period of exposure. 

Long Term Exposure Limits (LTELs)  

  • 8 hours to control effects by restricting the total intake over one or more work shifts  
  • The LTEL is designed to protect the workforce from concentrations of contaminants, which, over a large period of time, could cause long term chronic ill health effects.  
  • Monitoring and control methods are often used as working conditions such as repeated activity or regular shifts can make it difficult to prevent exposure.


If exposure cannot be prevented, then adequate controls must be implemented. But controls can only be considered adequate if:  

  • Workplace exposure limits (WEL) have not been exceeded.  
  • For carcinogens and sensitisers exposure is reduced to as low as reasonably practicable (ALARP)  
  • Principles of good practice have been applied  


COSHH Regulations How WELs Can Reduce The Risk To Health ECL

What If A Substance Is Not Assigned A WEL?  

There are so many chemical compounds and substances used in the workplace but often there isn’t enough safety information present on them, especially that outline accurate occupational exposure limits.

Not all substances used in the workplace have WEL values, but just because a substance doesn’t have a WEL, it doesn’t mean it’s safe.

COSHH Regulations state, exposure should still be controlled to a level which is safe for any hazardous substance to be created or used at work.

You can find out all current workplace exposure limits via the HSE publication EH40 Workplace Exposure Limits. These are revised routinely, with new entries added with each new edition.  

Example WELs  

Here are a few examples of substances which are hazardous to your health and their WELs:  

  • Hardwood Dust: 3mg/m3 8hr TWA  
  • Silica Dust (Respirable Crystalline): 0.1mg/m3 8hr TWA  
  • Flour Dust: 10mg/m3 8hr TWA
  • Welding Fume which consists of different substances (Some below):  
    • Iron Oxide: 5 mg/m3 8hr TWA  
    • Manganese (Inhalable): 0.2 mg/m3 8hr TWA  
    • Chromium: 0.5 mg/m3 8hr TWA  


As an employer, if you have hazardous substances in your workplace, it is important that these are controlled adequately.

Quantification of exposure, and thus verification as to whether or not adequate control is being achieved, can be carried out by undertaking Occupational Exposure Monitoring, which ECL are able to help you with.  

This process often involves samples being taken from the working environment and then analysed and compared against the previous levels data.


Workplace Exposure Monitoring  

The most effective way of understanding if exposure is currently within the workplace exposure limit or not, is by conducting workplace exposure monitoring.

Regulation 10 of the COSHH Regulations imposes a duty to monitor the exposure of employees to substances hazardous to health in certain specified situations.  

In order to assess exposure levels of airborne substances in the workplace, we can use sampling strategies such as personal / static air sampling, which measures the hazardous substance within the breathing zone of the worker or surrounding workplace air.   

This is executed by fitting portable air samplers to employees which draw air through a sorbent tube / filter, which can subsequently be analysed in a laboratory for contaminants known to be used in that particular process, in order to determine personal exposure. 

Where exposure to unknown contaminants is concerned, similar techniques may be employed in an attempt to identify then quantify any / all exposure. 

Current working practices should then be thoroughly assessed, and safety measures and control strategies improved where possible, with the aim of preventing or, at the very least, reducing exposure to hazardous substances.  

This could be achieved with engineering control measures like Local Exhaust Ventilation Testing or PPE, (which should always be a last means of exposure reduction).  

Workplace Exposure Monitoring should be carried out when a process changes, when new materials are introduced, a new plant is installed, or when a new or revised WEL is released for relevant substances used within your process. 

Routine, periodic monitoring may also be required / recommended depending upon the results of any initial sampling / exposure assessment. 


Your Workplace Exposure Limits Experts

ECL has numerous years of experience providing workplace air monitoring services to companies in the UK and around the world. 

All ECL Occupational Hygiene Services demonstrate compliance with Health & Safety best practice with all of our professional occupational hygienists competent to deliver an accurate, dependable, unbiased and fair service with:

  • The preparation of COSHH Risk Assessments.  
  • Monitoring exposure measurements and assessments for various substances.  
  • Assessment and evaluation of the effectiveness of control measures.
  • Local Exhaust Ventilation Testing. 

Call us on 01443 801215 or fill out our Enquiry Form for any queries regarding Workplace Exposure Limits, COSHH Air MonitoringVibration AssessmentsWorkplace Noise Assessments or any of our many other Environmental and Occupational Hygiene services.