LEV Hoods and Indicators
Understanding the Role of Performance Indicators in Local Exhaust Ventilation Systems
LEVCentral Expert Commentary
Few topics generate more debate within the LEV community than the question of airflow indicators and performance monitoring devices.
A common misconception is that UK legislation explicitly requires every LEV system to be fitted with an indicator. In reality, the position is more nuanced. Whilst COSHH does not specifically mandate the installation of an airflow indicator on every LEV system, HSE guidance consistently emphasises the importance of providing users with a practical means of confirming that the system is operating effectively.
The purpose of an indicator is not simply to satisfy a regulatory expectation. Its primary role is to provide early warning that system performance may have deteriorated. This allows operators and duty holders to identify potential problems before exposure control is compromised.
The most effective indicator is not always the most sophisticated. Depending upon the design and application of the LEV system, suitable performance monitoring may range from a simple pressure gauge or airflow indicator through to more advanced electronic monitoring systems. What matters is that the method selected is appropriate to the control strategy and can be understood by the people who rely upon it.
This paper by Bill Cassells, OXYL8 Ltd explores the relationship between LEV hoods, airflow performance and user monitoring, while clarifying the distinction between legal requirements and recognised good practice.
For duty holders, designers and LEV engineers alike, the key question should not be “Does the law require an indicator?” but rather “How will users know when control performance begins to deteriorate?”
Source Document
View the Indicators Paper here:
Source: Bill Cassells, OXYL8
Document Type: Briefing Note
Status: Current 2026
Last reviewed by LEVCentral: June 2026
Key Learning Points
- The COSHH Regs do not explicitly require an airflow indicator on every LEV system.
- HSE guidance expects users to have a practical means of determining whether an LEV system is operating correctly.
- Indicators provide an early warning of performance deterioration.
- Monitoring arrangements should be proportionate to the complexity and risk associated with the system.
- The effectiveness of an indicator depends upon user understanding and routine use.
- Performance monitoring should form part of the wider LEV management and maintenance strategy.
- A suitable indicator can support ongoing assurance between LEV Thorough Examination and Test (TExT) intervals.
Further Resources
- HSG258 – Controlling Airborne Contaminants at Work
- COSHH Regulations 2002 (as amended)
- OXYL8 Leadership Paper – “Defensible LEV Commissioning”
Recommended Learning
- P600 Performance Evaluation and Testing Methods for LEV
- P601 LEV Thorough Examination and Testing (TExT)
- P602 Basic Design Principles of LEV
- P604 LEV Commissioning and Baseline Performance Measurement
Thought Leadership
The discussion around indicators often focuses on legal compliance when it should focus on assurance. An indicator is valuable not because it satisfies a perceived requirement, but because it helps users recognise when performance may be changing.
In many respects, indicators represent one of the earliest links in the LEV assurance chain, providing operational evidence that a control measure continues to function between formal examinations and maintenance activities.
