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On the day

What happens during an LEV test?

An LEV test is a visit from a competent examiner, formally called a thorough examination and test. They inspect the extraction from hood to discharge, take airflow and pressure readings, watch smoke and dust move with the process running, then write up whether it still controls dust, fume and vapour. LEV testing is a check of how the system performs, not a service or a clean.

First published 22 September 2026. Checked 6 November 2026.

An engineer releases smoke at a capture hood edge to observe the inward airflow.
stages in an HSG258 test
3
checks on the stage 1 walk-round
8
reasons HSG258 gives for a red label
4

The visit in order

HSG258, the HSE guide to LEV, describes a test in three stages. Once access and permits are agreed, the visit follows this sequence:

Choose a step to see what happens.

  1. Paperwork

    The examiner checks the paperwork for the system: commissioning report, user manual, logbook and last report.

  2. Stage 1

    A walk-round looking at the condition of the hoods, ducts, filter, fan and alarms.

  3. Stage 2

    The process runs while the examiner watches smoke and dust, takes readings and calculates airflow.

  4. Stage 3

    The examiner weighs everything together and decides whether the LEV still controls exposure.

  5. Report

    Labels go on where used, and a written report follows with a prioritised list of any work needed.

Before the examiner arrives

Gather the commissioning report, user manual, logbook and previous report, plus any air sampling records relevant to the LEV, and tell the examiner about any change to the LEV, layout or process since the last test (HSG258 paragraph 334). The examiner should check that the documents describe the system in front of them.

The employer arranges permits to work and safe access, and tells the examiner what protective equipment is needed. The examiner has to know the risks of the job, such as residues inside the system, moving parts, work at height and electricity.

Tell staff the test is happening. For smoke tests the examiner should warn employees, and may have to switch smoke alarms off for the duration. Run the process as you normally would: the report records whether the test took place under normal production or special conditions, so do not stage a quiet day or hide a fault.

Stage 1: the walk-round

Stage 1 is a thorough visual and structural examination. HSG258 paragraph 338 says it should include, as appropriate:

Use this on the day: tick each check as the examiner makes it.

Stage 2: smoke, dust lamp and readings

Stage 2 reviews technical performance, and much of it happens with the process running. Smoke from tubes, pellets or generators shows where a cloud of dust or fume goes and whether the hood captures and contains it. Smoke generators can leave residues and are usually unsuitable where smoke detectors are fitted, unless these can be isolated, and pellets are inappropriate near flammable substances (paragraphs 292 and 293).

A dust lamp shows dust or mist escaping. The examiner sets it on a tripod, runs the process, stands off the line of the beam and looks up it towards the cloud, ideally against a dark background (paragraphs 290 and 291). Then come the readings, listed in the table.

The seven stage 2 checks, each drawn with its instrument or method. Choose one to see what it shows.
Checks in a stage 2 review and the instruments HSG258 names
CheckInstrument or methodWhat it shows
Air speed at each hood face, in the branch ducts and in the main ductAnemometer or Pitot tubeThe examiner can calculate volume flow and compare it with the design
Static pressure at the marked test points, covering hoods, ducting, air cleaner and fanManometerPressure in the hoods and ducting, and the drop across filters and fans
Fan speed, motor speed and power use, and the direction the fan turnsTachometer and power meterHow the fan is running, to set against the system documents
Make-up air supply, air temperatures and air cleaner performanceAs appropriate to the systemWhether the system has replacement air, and how the cleaner is performing
AlarmsSimulating a failureWhether an alarm detects the fault
Escape of dust or mistDust lampWhether anything gets out of the hood while the process runs
Movement of the cloudSmokeWhether smoke leaks, swirls back or reaches the breathing zone
A man in safety glasses and orange-cuffed gloves holds a handheld vane anemometer inside the open face of a steel canopy hood.
Air speed at a hood face, read with an anemometer.
A gloved hand holds a digital manometer, with a clear tube running to a small test point on a galvanised steel duct.
Static pressure, read at a marked test point on the ducting.

Comparing the readings, and what the examiner may adjust

The examiner calculates volume flow rates, compares the results with the design specification in documents such as the user manual, and works out the cause of any difference. Measurements alone do not prove that exposure is controlled, but they are kept as benchmarks for future tests.

With the employer's consent, the examiner may make a simple change that restores performance, such as rebalancing dampers that have moved. If the system is unsafe, the examination stops until it is repaired, and the examiner should warn the client promptly.

Stage 3: does it control exposure?

Stage 3 assesses control effectiveness. The examiner brings together the visual examination, observation of the process and how operators use the LEV, the challenge tests, the measurements and any air sampling records you hold. If these are acceptable, HSG258 says control should in nearly all circumstances be adequate and a test certificate issued (paragraphs 343 and 344).

Taking air samples is a separate job. HSG258 says it generally needs an occupational hygienist and may be needed where the hazard is great, so a test does not automatically include personal air monitoring (paragraphs 296 and 297).

If the test finds a fault

HSG258 gives four reasons for a red label: reduced or no detectable airflow, an enclosing hood that fails to contain the cloud, a receiving hood that fails to intercept or contain it, and a capturing hood whose capture zone does not cover the working zone (paragraph 346). HSE recommends a short written report with it, describing what is wrong and listing practical actions. Stop relying on that hood until a competent person has checked the repair.

Smoke Capture zone Breathing zone

Captured: the hood captures and contains the smoke, so none of it reaches the worker's breathing zone.

Escaping: smoke leaks out of the hood or reaches the breathing zone. This is what a smoke test looks for.

After the visit

The examiner judges whether the LEV is contributing effectively to your control of exposure and produces a prioritised plan for any action. Where repairs are priorities, you plan and schedule the repair and a retest to confirm control. Labels, how long to keep the record and how to read the report are covered in the guides to how often LEV testing is required, the regulations and understanding your LEV report, linked below.

What if there is no commissioning report?

The examiner needs to know what the system was meant to achieve. Where documents are missing, HSG258 says to ask the manufacturer first, then an LEV specialist such as a consultant engineer or occupational hygienist, or to ask the examiner to produce a commissioning report. That extra service and its cost have to be agreed (paragraphs 321 and 335).

LEV test, examination, inspection or assessment?

COSHH regulation 9 says "thorough examination and testing", and HSE's LEV FAQ shortens thorough examination and test to TExT. LEV test, LEV examination and LEV inspection are everyday names for the same job, and some companies call it an LEV assessment. It is not the regulation 6 risk assessment, which is a separate duty on the employer.

On-tool extraction

On-tool extraction counts as LEV, but HSE says only the extraction unit needs the full test: a visual check of its parts for damage or wear, then a performance measurement such as air velocity in a test hose. Hoods and hoses stay under regular checks and maintenance. The interval is covered in the guide to how often LEV testing is required.

Where to go next

This guide covers the day itself. Each of these takes one question further.

Where to read more on each part of the test
QuestionRead
What LEV testing is, in shortWhat is LEV testing?
How soon the next test is dueHow often is LEV testing required?
A date for your next testLEV test due date calculator
What COSHH requiresLEV testing regulations
How to read the report you getYour LEV test report and certificate explained
What the parts of an LEV system areWhat is local exhaust ventilation?
What the HSE guide coversHSG258 explained
What a test costsLEV testing cost
Picking a companyHow to choose an LEV testing company
Find a company near youLEV testing companies in the UK

Check what you know

4 quick questions from this guide. Nothing you choose is saved or sent.

  1. Which stage includes smoke and dust lamp tests with the process running?
    Show the answer

    Stage 2, the performance review. HSG258 paragraph 339 lists smoke challenge tests and dust lamp tests with the process running among the stage 2 checks.

  2. What does the examiner use to show dust or mist escaping from a hood?
    Show the answer

    A dust lamp. A dust lamp shows dust or mist escaping (HSG258 paragraphs 290 and 291). A manometer reads static pressure and an anemometer reads air speed.

  3. Does a test automatically include personal air monitoring?
    Show the answer

    No, taking air samples is a separate job. HSG258 paragraphs 296 and 297 say air sampling generally needs an occupational hygienist, so a test does not automatically include it.

  4. The examiner finds the system is unsafe. What happens?
    Show the answer

    The examination stops until it is repaired. HSG258 paragraph 342 says the examination should stop until an unsafe system has been repaired and its original performance restored, and the examiner should warn the client promptly.

Questions duty holders ask

What happens during an LEV test?

The examiner checks your paperwork, walks the system to inspect hoods, ducts, filter, fan and alarms, then watches smoke and dust with the process running and takes airflow and pressure readings. They judge whether it still controls exposure, then send a written report with any actions listed in priority order.

Does the process need to be running during an LEV test?

Yes, for part of the visit. HSG258 paragraph 339 lists smoke tests and dust lamp tests with the process running, so the examiner can see whether the hood captures the dust, fume or mist. The examiner should warn employees and may need smoke alarms turned off, so agree this before the visit.

Is an LEV assessment or inspection the same as an LEV test?

In everyday use, LEV examination, inspection and sometimes assessment all mean the LEV test. The regulation 6 risk assessment is different: it is a separate duty on the employer covering work with hazardous substances. Routine daily or weekly checks are also separate from the test.

What does an LEV inspection checklist cover?

HSG258 says the visual stage covers damage and wear on every part, the inside of the ducting, filter condition and cleaning devices, alarms, the fan drive, and signs of poor control such as settled dust near the hood or a noisy, vibrating part. Stage 2 adds airflow and pressure readings.

Is your next test due?

Put in the date of the last test and get the deadline, with a reminder if you want one.

LEV test due date calculator

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Sources

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