Ventilation Performance Assessment
Airflow & IAQ · Airflow & IAQ overview
Ventilation performance assessment evaluates how well a workplace ventilation system controls exposure and maintains air quality in real working conditions — not just how it looked when commissioned. It combines airflow measurement, system condition review, process observation and user-practice analysis into a single judgement about effectiveness.
What ventilation performance means
Performance is the difference between the ventilation a system is capable of and the ventilation it actually delivers when the workplace is operating normally. A nominally compliant LEV system can perform poorly if filters are loaded, hoods are out of position, operators work outside the capture envelope, or doors and draughts disrupt the airflow on which the system depends.
A performance assessment makes that gap visible. It identifies where installed plant is being defeated by maintenance, layout or behaviour, and where the underlying design is simply not adequate for the current process.
Installed condition versus real-world effectiveness
Statutory LEV testing under COSHH Regulation 9 confirms that a system meets its design benchmarks at the time of test. That is necessary but not sufficient. Effectiveness in use depends on whether operators routinely work within the capture envelope, whether the process has changed since commissioning, whether the building services around the system have changed pressure relationships, and whether the discharge is still going somewhere acceptable.
A performance assessment closes that loop. It compares the assumptions in the original design and risk assessment with what is happening on the floor, and reports the system's effective control level rather than its nominal capability.
What is reviewed
Performance assessment covers technical, operational and behavioural factors together. Looking at any single factor in isolation usually misses the real cause of poor control.
- Capture performance at sources, including hood geometry, flanging and distance from the emission point.
- System airflow rates and pressures relative to design and to current process load.
- Operator practice — posture, workpiece handling, time spent inside or outside the capture envelope.
- Source strength — whether the process now releases more or different contaminant than the system was designed for.
- Layout and obstructions, including stored materials, screens and partition changes that block air paths.
- Maintenance regime — filter changes, fan condition, instrumentation, leak repair and inspection records.
Prioritising improvements
Findings are prioritised by exposure significance, not just by how visible they are. A hood that captures 80% of a low-risk process matters less than a hood that captures 60% of a process generating respirable crystalline silica or welding fume reclassified as carcinogenic.
Recommendations typically fall into three tiers: maintenance and housekeeping that can be done in-house within weeks, engineering adjustments such as flanging, repositioning, partial enclosure or rebalancing that require a contractor visit, and capital actions such as new extraction plant or layout rework that need budget and lead time. Separating these tiers helps organisations act on what they can while planning for what they cannot.
Relationship with LEV testing and risk assessment
Performance assessment does not replace statutory LEV testing — it complements it. Where LEV testing answers 'does this system still meet its design benchmarks?', performance assessment answers 'is the control we are relying on actually working for the people exposed?'.
It also feeds the COSHH ventilation risk assessment by providing the evidence base for whether the chosen control strategy is suitable and sufficient. Organisations with mature exposure-control programmes use the two activities together: testing on the statutory cycle, performance assessment when something material changes or every one to two years as a planned review.
Frequently asked questions
Is a performance assessment a legal requirement?
There is no explicit statutory duty named 'performance assessment'. The duty under COSHH is to ensure control measures are effective and properly used. A documented performance assessment is one of the strongest ways to demonstrate compliance with that duty beyond the minimum 14-month LEV test.
How long does an assessment take?
A single process line can usually be assessed in a day on site, with a written report following. A whole-site programme covering multiple departments may take several days plus reporting time, depending on complexity and access.
Will the report stand up to HSE scrutiny?
Yes, provided it is methodologically traceable: calibrated instruments, defined sampling points, comparison to design and HSE guidance, photographic evidence and clear recommendations. That is the standard the assessment should be written to.
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