The Control of Substances Hazardous to Health Regulations 2002 require employers to assess and control exposure to hazardous substances at work. This includes dusts, fumes, vapours, gases, and biological agents. A COSHH assessment must be carried out before work begins.

What are Workplace Exposure Limits (WELs)?

WELs are the maximum concentration of a substance in the air that workers can be exposed to over an 8-hour period (LTEL) or 15-minute period (STEL). They are published in HSE EH40. Common construction WELs: silica 0.1 mg/m3, wood dust 3 mg/m3, cement dust 1 mg/m3.

What RPE do I need for construction dust?

For silica dust (cutting concrete, stone): minimum FFP3 (APF 20). For wood dust: minimum FFP2 (APF 10) for softwood, FFP3 for hardwood. For general construction dust: FFP2 minimum. All tight-fitting RPE must be face-fit tested annually.

What is an Assigned Protection Factor (APF)?

APF indicates how much a respirator reduces exposure. APF 10 means it reduces exposure by 10x, APF 20 by 20x, APF 40 by 40x. The protected exposure = actual exposure / APF. Choose RPE where the protected exposure is below the WEL.

Do I need COSHH assessments as a sole trader?

Technically, COSHH applies to employers, but the duty to manage your own health exists under the Health and Safety at Work Act. In practice, principal contractors require COSHH assessments from all workers on site. Many accreditation schemes also require them.

TradeCalculator

COSHH Assessment Calculator

Check substance exposure against Workplace Exposure Limits

Substance

Estimated Airborne Level

Exposure Duration

RPE Type

How We Calculate This

Select the hazardous substance to look up its Workplace Exposure Limit (WEL), or enter a custom value. Input your estimated airborne concentration and exposure duration. The calculator computes the 8-hour time-weighted average (TWA) exposure, applies the RPE Assigned Protection Factor if selected, and compares the result against the WEL to determine compliance. It also calculates the minimum APF needed if current protection is inadequate.

Frequently Asked Questions

Related Calculators

Manual Handling Assessment Calculator

Calculate manual handling risk score from weight, frequency, distance and posture.

Noise Exposure Calculator

Calculate daily noise exposure LEP,d from tool dB levels and duration.

HAV Exposure Calculator

Calculate hand-arm vibration exposure points from tool vibration and trigger time.

Dust Exposure Calculator

Calculate dust exposure against WEL limits with extraction rate and RPE factor.

CDM Notification Calculator

Determine CDM F10 notification requirement from project duration and worker numbers.

Last updated: March 2026

All calculations are estimates. Verify with your supplier.