Local Exhaust Ventilation Testing: The Complete UK Employer's Guide

Local exhaust ventilation testing is a legal requirement for every UK employer who operates an LEV system. Under the Control of Substances Hazardous to Health Regulations 2002 (COSHH), your LEV must be thoroughly examined and tested at regular intervals to confirm it's working effectively. The examination is carried out by a competent person, and the results are recorded in a formal report you must keep for at least 5 years.

This guide covers everything UK employers need to know about local exhaust ventilation testing — from the legal basis through to the practical steps you can take to stay compliant.

What Local Exhaust Ventilation Testing Is

Local exhaust ventilation testing — formally called a thorough examination and test, or TExT — is a structured assessment of your LEV system's condition and performance. It goes well beyond a visual check. A TExT involves physical inspection of every component, quantitative measurements of airflow and capture performance, and a professional judgement about whether the system is providing adequate control of airborne contaminants.

The purpose is simple: to confirm that the LEV system installed to protect your workers is actually doing its job. Systems deteriorate. Filters clog. Ducts develop leaks. Fan performance drops. Components get damaged or modified. Without regular testing, you have no way of knowing whether your extraction system is still effective.

For a fuller explanation of what LEV is and why it matters, see our guide on what LEV stands for.

The Legal Basis

COSHH Regulation 9

The requirement for LEV testing comes from COSHH Regulation 9. This regulation states that every LEV system provided to control exposure to hazardous substances must be maintained in an efficient state, in efficient working order, in good repair, and in a clean condition.

It further requires that LEV systems are thoroughly examined and tested by a competent person at suitable intervals. For most LEV systems, that interval is a maximum of 14 months. Some processes have shorter intervals specified in COSHH Schedule 4 — for example, certain processes involving lead or specific chemicals may require examination every 6 months.

The 14-month maximum is not a target. It's a deadline. If your system was last tested on 1 January 2026, it must be tested again by 1 March 2027 at the latest. Miss that window and you're in breach of COSHH. See our detailed guide on how often LEV should be tested for more on the timing rules.

Record-keeping

COSHH Regulation 9 also requires that the results of every TExT are recorded and that records are kept for at least 5 years. The record must contain specific information set out in HSG258. Failure to keep adequate records is itself a breach, even if the testing was actually carried out. For guidance on record-keeping, see our comparison of paper vs digital LEV log books.

HSG258

HSG258 is the HSE's technical guidance document that underpins LEV testing. While not legislation itself, it's the standard inspectors use to judge whether an examination was thorough enough and whether the report is adequate. Our HSG258 explainer covers the key chapters.

Types of Testing Carried Out During a TExT

A thorough examination and test isn't a single activity. It's a combination of different assessment methods, each checking a different aspect of the system's performance.

Visual inspection

The examiner inspects every visible component of the LEV system. This includes hoods and capture points, flexible and rigid ductwork, joints and connections, dampers and blast gates, the fan unit, the air cleaning device (filters, collectors, cyclones), and the discharge point.

They're looking for physical damage, corrosion, wear, dust buildup, disconnections, modifications since the last examination, and anything that could reduce the system's performance or create a safety risk.

Measurement of capture velocities

Capture velocity is the air speed at the point where the LEV hood captures contaminants. The examiner uses an anemometer to measure air velocity at the face of each hood or at specified distances from the capture point.

These measurements confirm whether the system is generating enough airflow to capture contaminants before they escape into the worker's breathing zone. Inadequate capture velocity is one of the most common reasons for a TExT failure.

Airflow measurements

The examiner measures the volume of air moving through the system, typically at the hood face and at key points in the ductwork. These measurements are compared against the system's design specifications (if available) or against HSG258 guidance values.

Declining airflow over successive examinations indicates the system is losing performance — possibly due to filter loading, duct blockages, or fan deterioration.

Static pressure measurements

Static pressure readings taken at various points in the ductwork help diagnose system problems. Pressure drops across filters indicate filter loading. Pressure differences between duct sections can reveal blockages or leaks. The examiner uses a manometer to take these readings.

Smoke or tracer tests

The examiner may use a smoke tube, smoke pencil, or other tracer to visualise airflow patterns at the capture point. This reveals whether the hood is capturing contaminants effectively, whether there are disruptive draughts interfering with capture, and whether the direction of airflow is correct.

Smoke testing is particularly useful for showing problems that measurements alone might miss — for example, a cross-draught from an open door that periodically pushes contaminants past the hood.

Filter integrity testing

For systems with filtration — bag filters, cartridge filters, HEPA filters — the examiner checks filter condition, seal integrity, and whether the air cleaning device is actually removing contaminants. A torn filter bag, a poorly seated cartridge, or a damaged seal can allow contaminants to pass through the system and be discharged back into the workplace.

Ductwork condition assessment

Beyond visual inspection, the examiner may check ductwork for internal dust accumulation, corrosion, and leak points. Excessive dust buildup in ducts indicates transport velocities are too low — the system isn't moving air fast enough to carry particles to the collector. This reduces system performance and, for combustible dusts, creates a fire or explosion risk.

What the Examiner Does: Step by Step

Understanding the process helps you prepare and know what to expect.

1. Review documentation. The examiner starts by reviewing any existing documentation — previous TExT reports, the system's original commissioning data (if available), and maintenance records. This gives them a baseline to work from and highlights any previously identified issues.

2. System walkthrough. The examiner walks the entire system from hood to discharge, noting the general condition, layout, and any visible problems. They'll identify all the measurement points they need to access during the examination.

3. System operating checks. With the system running under normal operating conditions, the examiner checks that all components are functioning — fans running, dampers set correctly, hoods positioned properly.

4. Quantitative measurements. The examiner takes measurements at each hood (capture velocity, face velocity), at duct measurement points (transport velocity, static pressure), across the air cleaner (pressure drop), and at the fan (operating point). These measurements form the quantitative core of the report.

5. Smoke or tracer testing. At each capture point, the examiner may use smoke to visualise airflow and confirm that contaminants are being captured effectively under actual working conditions.

6. Filter and air cleaner assessment. The air cleaning device is inspected for condition, loading, and integrity. The examiner checks that the device is functioning correctly and that cleaned air meets the required standard.

7. Assessment and reporting. Based on all observations and measurements, the examiner forms a professional judgement about whether the system is in efficient working order and provides adequate control. They compile their findings into a written report with measurements, defects, recommendations, and a compliance statement.

The entire process takes anywhere from one to several hours per system, depending on complexity.

What Happens After the Test

You receive a report

The examiner produces a written report that becomes your compliance record. This report must contain all the information specified in HSG258. See our guide on what a TExT report must include for the full list of required contents.

You act on the findings

If the report identifies defects or makes recommendations, you need to act on them. Some defects require immediate action — particularly anything that means the system isn't providing adequate control. Others may be scheduled for the next maintenance window.

Record what action you took and when. This creates evidence that you responded to the examination findings — which is exactly what the HSE expects to see.

You schedule the next examination

The report will state when the next TExT is due. Record this date and set reminders. Use the LEV testing due date calculator to confirm the deadline and set up alerts. The most common compliance failure is simply letting the 14-month window expire.

How Much Does LEV Testing Cost?

Typical TExT costs in the UK range from £150 to £400 per system, depending on the type and complexity of the LEV, the number of systems being examined, accessibility, and geographic location. For a detailed breakdown of pricing factors and budgeting tips, see our guide on LEV testing costs.

How to Prepare Your LEV System for Testing

Preparation reduces wasted time during the examination and can lower the cost. It also demonstrates to the examiner that the system is being actively managed.

Make the system accessible. Clear obstructions from around hoods, ductwork, and the air cleaning device. The examiner needs to reach measurement points, inspect components, and access the fan unit. If equipment is stored in front of ductwork or the filter unit is blocked in, move it before the examiner arrives.

Have the system running. The examination is carried out with the system operating under normal conditions. Make sure the system is switched on and running before the examiner starts. If specific machines or processes need to be running during the test, coordinate this in advance.

Gather your documentation. Have the previous TExT report available. If you have commissioning data, design specifications, or a system schematic, have those ready too. Maintenance records and user check logs help the examiner understand the system's history.

Complete any outstanding maintenance. If you know about problems — a filter that needs changing, a damaged flexible connection, a hood that's been repositioned — fix them before the examination. Don't pay for an examiner to document known faults. Deal with them in advance so the examination focuses on finding things you don't know about.

Brief the examiner. If there are access constraints, time restrictions, or specific concerns about the system, tell the examiner at the start. If workers have reported reduced extraction performance or unusual noises, mention it. The examiner can investigate known concerns during their assessment.

Ensure blast gates and dampers are set correctly. If your system has blast gates or volume control dampers, check they're in the correct positions before the examination starts. A blast gate left closed on a branch the examiner wants to test wastes time. Set gates to reflect normal operating conditions.

Common Test Failures and How to Prevent Them

Understanding why LEV systems fail their TExT examination helps you avoid the same problems.

Low capture velocity

The most common failure. The hood isn't capturing contaminants effectively. Causes include blocked filters (increasing system resistance and reducing airflow), leaking ductwork (airflow escaping before it reaches the hood), worn fan belts (reducing fan speed and output), or hoods positioned too far from the dust source. Regular maintenance between inspections prevents most of these.

Ductwork damage or leaks

Flexible ductwork degrades over time — kinks, tears, collapsed sections. Rigid ductwork develops corrosion holes or leaking joints. Every leak reduces the airflow reaching the hood. Inspect ductwork regularly as part of your user checks and repair damage promptly.

Blocked or overloaded filters

A filter at capacity can't pass air. System resistance climbs. Airflow drops. Capture performance deteriorates. Monitor filter condition and differential pressure regularly. Change filters before they reach the point of restricting airflow.

Incorrect damper or blast gate settings

If your system has multiple branches with blast gates, incorrect settings redirect airflow away from where it's needed. Ensure all gates are set for normal operating conditions and that staff understand how to set them correctly.

Modified or repositioned hoods

Hoods get moved, bent, or removed to make way for other activities. A hood that's no longer in the correct position relative to the dust source won't capture effectively, even if the system behind it is performing well. Check hood positions regularly and fix any that have moved.

Fan problems

Worn belts, misaligned pulleys, bearing wear, motor faults — all reduce fan output. Listen for unusual noises. Check belt tension. Monitor fan performance through static pressure readings. Address problems early.

Inadequate transport velocity

If duct transport velocities are too low, dust settles in the ductwork instead of being carried to the collector. This progressively restricts the duct, further reducing velocity, creating a worsening cycle. Adequate transport velocity depends on the type of dust — heavier particles need higher velocities.

Staying on Top of Compliance

LEV testing is not a one-off event. It's a recurring obligation that runs for as long as you operate LEV systems. The key to managing it is structure: know your deadlines, keep your records, maintain your systems between examinations, and act on examination findings.

The LEV compliance checklist generator can help you build a structured compliance framework tailored to your systems. The record-keeping requirements checker confirms your documentation meets COSHH requirements.

LEVproof is being built to manage your LEV testing schedule, store examination reports, track maintenance, and send automated reminders before deadlines expire. Join the waitlist for early access.

Sources

• Control of Substances Hazardous to Health Regulations 2002 (COSHH) — legislation.gov.uk
• HSG258: Controlling airborne contaminants at work — HSE
• LEV guidance for employers — HSE
• Local exhaust ventilation (LEV) guidance — HSE
• COSHH main page — HSE
• Work-related lung disease — HSE

This guide summarises published HSE and government guidance. It does not constitute legal advice. Consult a qualified professional for advice specific to your situation.