LEV Testing
LEV Testing · LEV Testing overview
LEV testing is the structured measurement and inspection of a local exhaust ventilation system against its original design intent and against HSE benchmarks in HSG258. It tells the duty-holder whether the system is still controlling exposure as intended, whether it has drifted, and what action is needed to bring it back into a defensible condition.
What LEV testing checks
LEV testing is more than a quick visual inspection. A competent test combines documented system understanding with instrument measurement and direct observation of the system in use. The goal is to verify that the LEV, as installed and as currently operated, still captures, transports and removes the airborne contaminant it was specified to control.
On every visit, the examiner builds up a picture of three things: how the system was designed to perform, how it is performing now, and how it is actually being used by operators.
Why LEV testing matters
Local exhaust ventilation degrades over time. Filters load, ductwork accumulates internal dust, fan belts slip, dampers shift, hoods get damaged or relocated, and processes evolve. None of this is necessarily visible to operators who use the system every day, and exposure to many of the substances LEV controls — welding fume, hardwood dust, solvent vapour, isocyanate mist, respirable crystalline silica — produces no immediate sensation at exposures that are still harmful.
Regular LEV testing is the mechanism by which employers convert assumed control into demonstrated control. It also supports the COSHH duty to keep records of examination and test for at least five years, which forms a key part of an organisation's defensible audit trail.
What is measured and observed
A competent LEV test follows the HSG258 methodology. The specific measurements depend on hood type, system size and contaminant — not every parameter is relevant to every system — but the toolkit normally includes:
- Hood static pressure, measured close to the hood, to confirm the system is drawing the design airflow.
- Face velocity at booths, partial enclosures and fume cupboards, traversed across the opening to a defined grid.
- Capture velocity at the point of release, where this can be measured safely and meaningfully.
- Duct transport velocity at sample points, to confirm contaminants remain entrained and do not settle out.
- Pressure drop across filters and air cleaners, indicating loading and remaining service life.
- Fan condition — drive arrangement, belt tension, motor current where accessible, vibration and noise.
- Visual condition of hoods, flexible connections, ductwork, dampers and discharge points.
- Operator practice — how the system is actually used, working position relative to the hood, and whether bypass behaviours have developed.
Testing, inspection and performance review
These three terms are sometimes used interchangeably, but they describe different activities.
A statutory thorough examination and test (TExT) is the formal COSHH Regulation 9 check, delivered to HSG258 by a competent examiner, with a written report. An interim inspection is the lighter, in-house check carried out by maintenance or operators between statutory tests — useful for catching gross changes but not a substitute for TExT. A ventilation performance review is broader still: an engineering judgement about whether the system, even if performing as designed, is the right control for the current process.
What a practical LEV testing visit may include
A typical LEV testing visit to a UK site begins with a documentation review — original commissioning data, the user manual, previous test reports and any recent process or layout changes. The examiner then walks the system in operation, identifies hoods and measurement points, and carries out the instrument measurements above. Each hood is judged against its benchmark — face velocity for booths, capture velocity for slot or canopy hoods, static pressure for installed monitoring points.
Observations of operator behaviour, condition findings and out-of-tolerance measurements are written up in a report that classifies each hood as performing as intended, performing below benchmark but acceptable, or failing — together with clear, prioritised remedial actions.
Common failures found during LEV testing
The same problems recur across UK industry. Recognising them helps duty-holders correct issues before the next test rather than discovering them in a failed report.
- Hoods sited too far from the source for capture velocity to be effective at the working position.
- Flexible duct lengths well in excess of the original design, with concertina folds that destroy transport velocity.
- Damaged or missing baffles, slot covers and flanges that the original design relied on.
- Filter banks operated long past their differential-pressure alarm threshold.
- Booth lighting and air-knife discharges that disrupt the booth's intended airflow pattern.
- Operator working position outside the capture envelope, especially on portable on-torch and on-tool extraction.
How reports support compliance and improvement
An LEV test report is both a compliance record and an engineering document. The compliance role is satisfied by demonstrating that a competent examination took place, what was found, and what action was taken. The engineering role is satisfied by giving managers a clear, prioritised list of what to fix, in what order, to restore or improve control.
Reports written purely as box-ticking exercises help no one. A useful report names the hoods, references the original benchmark, gives the measured value, gives the verdict, and gives a recommended action with an indicative timeframe.
Frequently asked questions
How often does LEV need to be tested?
COSHH Regulation 9 requires LEV used to control exposure to a hazardous substance to be thoroughly examined and tested at least every 14 months. Some processes — for example certain pharmaceutical and chemical operations listed in Schedule 4 of COSHH — require more frequent testing.
Does the operator need to be present during LEV testing?
Testing is normally carried out with the system running as it does in production, which usually means operators are present and the process is operating. Observing real working practice is a key part of an HSG258-compliant examination.
What happens if the LEV fails the test?
A failed hood or system does not automatically mean immediate shutdown — it means the duty-holder must take action proportionate to the risk. The report will identify which hoods are failing, why, and what remediation is required. Significant failures may warrant interim controls such as additional PPE or process restrictions until repairs are completed.
Can LEV testing be done in-house?
Routine visual checks and basic monitoring can and should be done in-house between statutory tests. The 14-monthly thorough examination should be carried out by a competent person — competence is described in HSG258 and typically demonstrated through BOHS P601 qualification and documented experience.
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