HSE Guide G408 “Urine Sampling for Isocyanate Exposure Measurement”
Understanding Biological Monitoring and the Effectiveness of Exposure Controls
LEVCentral Expert Commentary
Isocyanates remain one of the most significant causes of occupational asthma in the UK, particularly in industries involving spray painting, polyurethane products, adhesives, foams and certain construction materials. As a result, employers must ensure that exposure is adequately controlled and that control measures continue to perform effectively.
HSE Guidance G408 explains the role of urine sampling as a form of biological monitoring for isocyanate exposure. Unlike air sampling, which measures contaminants in the workplace environment, urine testing measures the breakdown products of isocyanates that have actually entered the body. This provides valuable information on the effectiveness of exposure controls, respiratory protective equipment (RPE) and working practices.
One of the most important messages within the guidance is that urine sampling should not be viewed as a replacement for air monitoring. Rather, it provides an additional layer of assurance by confirming whether workers are being exposed despite existing control measures. Where biological monitoring identifies unexpected exposure, employers should investigate the effectiveness of engineering controls, RPE, training and working practices.
For occupational hygienists, LEV professionals and duty holders, G408 provides a practical introduction to biological monitoring and demonstrates how health surveillance, exposure monitoring and engineering controls can work together to provide a more complete picture of workplace exposure risk.
Source Document
View the HSE guidance here:
Source: Health and Safety Executive (HSE)
Document Type: COSHH Essentials Guidance
Status: Current 2026
Last reviewed by LEVCentral: June 2026
Key Learning Points
- Isocyanates are a recognised cause of occupational asthma.
- Urine sampling measures biological uptake rather than airborne concentration.
- Biological monitoring helps assess the effectiveness of control measures and RPE.
- Urine testing supplements, but does not replace, air sampling.
- Unexpected biological monitoring results should trigger a review of workplace controls.
- Monitoring can help identify exposure pathways that may not be evident from air sampling alone.
- Biological monitoring forms part of a wider occupational health and exposure control strategy.
Further Resources
- HSE G402 – Health Surveillance for Occupational Asthma
- HSE G409 – Exposure Measurement: Air Sampling
- HSG258 – Controlling Airborne Contaminants at Work
- EH40 Workplace Exposure Limits
- BOHS Guidance on Isocyanate Exposure Monitoring
Recommended Learning
- M200 Basic Principles in Occupational Hygiene
- M501 Measuring Hazardous Substance
- M507 Health Effects of Hazardous Substances
- P304 Fundamentals of CoSHH Risk Assessment & Control
- P604 Commissioning and Performance Evaluation of LEV
- P603 CoSHH PPE
Thought Leadership
Effective exposure control is rarely demonstrated by a single measurement technique. Air monitoring shows what is present in the workplace environment, whilst biological monitoring helps determine what has actually entered the body.
When considered together, these approaches provide a more complete understanding of exposure risk and the effectiveness of workplace controls.
For organisations working with isocyanates, biological monitoring can provide valuable assurance that control measures are achieving their intended purpose.
