BS EN 689 2018 “Measuring Exposure by Inhalation to Chemical Agents”
BS EN 689:2018 – Measuring Exposure by Inhalation to Chemical Agents
BS EN 689:2018 is the principal European standard for assessing occupational exposure to airborne hazardous substances. It provides a structured methodology for determining whether worker exposure is adequately controlled and whether compliance with Workplace Exposure Limits (WELs) can be demonstrated.
The standard sets out a framework for:
- Exposure assessment planning
- Similar Exposure Groups (SEGs)
- Initial workplace appraisal
- Exposure measurement strategies
- Statistical evaluation of results
- Compliance testing against occupational exposure limits
- Periodic reassessment requirements
- Ongoing exposure management
The standard is widely used by occupational hygienists, regulators, laboratories and employers when designing exposure-monitoring programmes and interpreting airborne contaminant data.
This resource is relevant to:
- Occupational Hygienists
- Exposure Monitoring Specialists
- LEV Consultants
- Health & Safety Professionals
- COSHH Assessors
- Duty Holders
- Laboratory Analysts
- Process Engineers
- Regulatory Inspectors
Source Document
View the BSI Standard here:
Source: British Standards Institute (BSI)
Document Type: BS EN Standard
Status: 2019
Last reviewed by LEVCentral: June 2026
LEVCentral Expert Commentary
BS EN 689:2018 is arguably one of the most important occupational hygiene standards in use today because it provides the framework for answering a fundamental question:
“How do we know workers are adequately protected from airborne hazardous substances?”
The standard recognises that a single air sample rarely provides enough information to assess exposure reliably. Instead, it adopts a structured statistical approach that considers variability between workers, tasks, shifts and operating conditions. The concept of Similar Exposure Groups (SEGs) is central to the methodology, allowing workers undertaking comparable activities to be assessed as a group rather than individually. This improves the efficiency and reliability of exposure assessments.
For LEV professionals, BS EN 689 is particularly important because it bridges the gap between engineering performance and occupational exposure. A ventilation system may achieve its design airflow and pass a Thorough Examination and Test (TExT), yet workers may still experience significant exposure due to work practices, process variability, poor hood positioning or other operational factors.
The standard therefore reinforces an important principle:
Engineering performance does not automatically equate to exposure control.
Where there is uncertainty regarding actual worker exposure, personal air monitoring may be required to confirm that engineering controls are delivering the intended level of protection. BS EN 689 provides the framework for undertaking this assessment in a consistent and statistically defensible manner. The standard also establishes requirements for periodic reassessment to ensure that exposure remains controlled over time and is not simply assessed as a one-off exercise.
For organisations seeking defensible COSHH compliance, BS EN 689 should be viewed as a cornerstone document supporting exposure monitoring programmes and occupational hygiene strategies.
Key Learning Points
Similar Exposure Groups (SEGs)
The standard groups workers with similar exposure profiles into SEGs, enabling representative sampling strategies and more meaningful statistical interpretation.
Exposure Assessment Is an Ongoing Process
BS EN 689 recognises that workplace exposure can change due to:
- Process modifications
- Changes in materials
- Production increases
- Maintenance issues
- Worker behaviours
Regular reassessment is therefore essential.
Statistics Matter
The standard introduces statistical tools to evaluate whether exposure is likely to remain below occupational exposure limits over time, rather than relying solely on individual sample results.
Supports COSHH Compliance
The methodology provides a recognised framework for demonstrating compliance with the requirements of COSHH and workplace exposure limit assessments.
Further Resources
- HSG173 – Monitoring Strategies for Toxic Substances
- EH40 Workplace Exposure Limits
- BOHS “Testing Compliance with Occupational Exposure Limits”
- COSHH Approved Code of Practice (L5)
- HSG258 – Controlling Airborne Contaminants at Work
Recommended Learning
- M200 Basic Principles of Occupational Hygiene
- M501 Measurement of Hazardous Substances
- P304 COSHH Risk Assessment Fundamentals
- P604 LEV Performance Evaluation and Management
Thought Leadership
BS EN 689 reflects a wider shift in occupational hygiene away from simple compliance monitoring towards risk-based exposure management.
Historically, exposure assessments often focused on collecting a small number of samples and comparing them directly with exposure limits. Modern occupational hygiene increasingly recognises that exposure varies from day to day and that effective risk management requires an understanding of exposure patterns rather than isolated measurements.
For LEV professionals, this standard provides a useful reminder that exposure control should ultimately be judged by the protection afforded to workers, not solely by engineering measurements. The strongest occupational health programmes integrate exposure monitoring, LEV performance verification, health surveillance and competent management systems into a single evidence-based control strategy.
