Respirable crystalline silica (RCS) is one of the most significant long-term health hazards in construction, demolition, quarrying, and aggregate environments. Because silica is present in many common building materials, exposure is difficult to avoid — but it must be controlled.
Under UK law, the Workplace Exposure Limit (WEL) for respirable crystalline silica is:
0.1 mg/m³, averaged over an 8-hour time-weighted average (TWA).
This limit is set under the Control of Substances Hazardous to Health Regulations 2002 (COSHH) and must not be exceeded.
In this guide, we explain what the WEL means in practice, how exposure is measured, and what employers must do to stay compliant.
What is Respirable Crystalline Silica (RCS)?
Silica is a naturally occurring mineral found in materials such as concrete, mortar, brick, sandstone, granite, slate, and artificial stone. When these materials are cut, drilled, crushed, or ground, fine dust particles are released into the air.
The smallest particles — known as respirable crystalline silica — are small enough to penetrate deep into the lungs. Over time, repeated exposure can lead to serious and irreversible health conditions including silicosis, COPD, and lung cancer.
If you’re unfamiliar with the wider risks, our guide on how to reduce the risk of exposure to silica dust explains how RCS affects the lungs and what practical steps can be taken to minimise harm.
What does the 0.1 mg/m³ WEL mean?
The WEL of 0.1 mg/m³ is measured as an 8-hour time-weighted average (TWA).
A time-weighted average means exposure is averaged across a typical working day. Workers may be exposed to higher concentrations for short periods, but overall exposure across 8 hours must not exceed 0.1 mg per cubic metre of air.
For example:
If a worker is exposed to 0.2 mg/m³ for 4 hours, they would reach the 8-hour WEL. No further exposure should occur that day.
It’s important to understand that the WEL is a legal maximum — not a “safe target.” Under COSHH, exposure must be reduced as far as reasonably practicable, even if levels are technically below the WEL.
Is there a short-term exposure limit for silica?
Respirable crystalline silica does not have a specific short-term exposure limit (STEL) in the UK. However, as a general guide, exposure should not exceed three times the WEL (0.3 mg/m³) over a 15-minute period.
Even short bursts of high exposure can significantly increase long-term health risks, particularly during high-dust activities such as demolition or concrete grinding.
For example, if you’re carrying out grinding works, effective dust control measures are critical. We explore practical solutions in our article on how to reduce dust when grinding concrete.
What do employers legally have to do?
Under COSHH, employers must:
- Carry out a suitable and sufficient risk assessment
- Prevent or adequately control exposure
- Ensure exposure does not exceed the WEL
- Apply the principles of good control practice
- Monitor exposure where necessary
- Provide health surveillance where appropriate
Adequate control is only achieved when:
- Engineering controls are in place
- The WEL is not exceeded
- Exposure is reduced as low as reasonably practicable
For a broader overview of dust-related legal responsibilities on site, see our Construction Dust Safety Guide.
How is silica exposure measured?
Exposure to respirable crystalline silica is measured through air sampling. This may involve:
- Personal sampling devices worn in the breathing zone
- Static air monitoring equipment placed in work areas
- Laboratory analysis of collected dust samples
Monitoring is especially important during high-risk activities such as demolition, crushing, and aggregate handling. Where exposure approaches the WEL, control measures must be reviewed and strengthened.
How can you keep exposure below the WEL?
The most effective way to stay compliant is to control dust at source.
Engineering controls significantly reduce airborne dust before it reaches workers. These include:
- Wet cutting and water suppression
- On-tool extraction systems
- Local exhaust ventilation
- Dedicated dust suppression equipment
Ace Plant provides a wide range of dust suppression equipment suitable for construction and demolition environments:
Depending on your site requirements, this may include:
These systems help prevent airborne silica dust from building up across the work area.
For a full overview of available methods, see what dust suppression is and the best dust suppression solutions:
In addition to engineering controls, safe working practices should include:
- Avoiding dry sweeping
- Using wet cleaning or M/H-class vacuums
- Restricting access to high-dust areas
- Maintaining equipment properly
Respiratory Protective Equipment (RPE)
RPE should only be used as a final layer of protection when dust cannot be fully controlled at source. It must be correctly selected, face-fit tested, and maintained.
Why staying well below the WEL matters
The WEL is not a guarantee of safety — it is a legal ceiling. Silica is classified as a carcinogen, and cumulative exposure over time can result in irreversible lung damage.
By implementing effective dust suppression and site controls, employers can:
- Protect worker health
- Reduce long-term liability
- Avoid enforcement action
- Maintain productivity without disruption
Ace Plant supplies a wide range of professional dust suppression solutions designed for UK construction and industrial environments. Whether you require a compact mobile unit or high-capacity mist cannon, our team can help you choose the right equipment for your site.
Contact our team to discuss your site requirements and ensure your project remains compliant with COSHH and WEL guidance.