LEV Risk Assessment Guide: How to Assess Whether Your Ventilation Is Adequate

Before you can determine what LEV you need — or whether what you have is good enough — you need a risk assessment. This isn't a separate process from your COSHH assessment. LEV sits directly within it. The risk assessment tells you whether airborne contaminants are a problem, what controls are needed, and whether your existing controls actually work.

If you operate processes that generate dust, fume, vapour, or mist, this applies to you.

What a COSHH Risk Assessment Is

The COSHH Regulations 2002 require employers to assess the risks to health from hazardous substances in the workplace. Regulation 6 sets out this duty. The assessment must identify what hazardous substances are present, who might be exposed, and what control measures are needed.

LEV enters the picture when the assessment identifies airborne contaminants that need controlling. Under COSHH's hierarchy of control, the preferred approach is:

Eliminate the substance or process entirely
Substitute with a less hazardous alternative
Enclose the process to prevent release
Local exhaust ventilation to capture contaminants at source
General ventilation to dilute residual airborne levels
Personal protective equipment as a last resort

LEV sits at step 4. If you can't eliminate, substitute, or fully enclose the process, LEV is the next control in the hierarchy. It's not optional when the higher-tier controls aren't practicable.

When an LEV Risk Assessment Is Needed

You need to assess LEV requirements whenever a work process generates airborne contaminants. The common triggers:

Dust. Woodworking, stonecutting, grinding, sanding, milling, flour handling, pharmaceutical processing. Any mechanical action on a solid material that produces airborne particles.

Fume. Welding, soldering, brazing, hot-dip galvanising, smelting. Thermal processes that generate metallic or chemical fume.

Vapour. Spray painting, degreasing, adhesive application, printing, chemical mixing. Processes involving volatile liquids that evaporate into breathable vapour.

Mist. Metalworking fluid spray, electroplating, some cleaning operations. Liquid aerosols generated by mechanical action or pressurised application.

If any of these are present in your workplace, your COSHH risk assessment must address them — and that assessment must consider whether LEV is needed.

Step-by-Step Risk Assessment Process

Step 1: Identify the hazardous substances

List every substance your processes generate or use that could become airborne. Be specific:

What is it? Name the substance. "Dust" isn't specific enough. Is it hardwood dust, MDF dust, silica dust, welding fume, isocyanate vapour? The identity determines the workplace exposure limit and the level of risk.
What form does it take? Dust, fume, vapour, mist — the form affects how it behaves in air and what extraction approach is needed.
What's the workplace exposure limit? Check EH40 for the relevant WEL. Some substances have very low limits (welding fume: 1 mg/m³; hardwood dust: 3 mg/m³). Others have higher limits but still require control.
What are the health effects? Carcinogenic, sensitising, irritant, toxic? The severity of potential health effects determines how rigorous your controls need to be. The HSE's lung disease guidance covers the most common occupational respiratory hazards.

Step 2: Assess the exposure

Determine who is exposed, how, and how much.

Who is exposed? The machine operator, nearby workers, people in adjacent areas, maintenance staff, cleaners?
How are they exposed? Directly at the point of generation? From background contamination that drifts across the workshop? During cleaning or maintenance?
What's the duration and frequency? Full-shift exposure every day is very different from 20 minutes of exposure twice a week. But even short-duration, high-concentration exposure can exceed the WEL.
What's the current exposure level? If you already have LEV or other controls, are they reducing exposure adequately? Air monitoring — either personal sampling or static sampling — can provide objective data. Without monitoring, you're estimating.

Step 3: Determine the controls needed

Based on what you've identified, work through the COSHH hierarchy:

Can you eliminate the substance? Switch to a dust-free process, use pre-cut material, reformulate with a non-hazardous alternative?
Can you substitute? Water-based paints instead of solvent-based. Lower-dust abrasives. Lower-fume welding consumables.
Can you enclose? A sealed grinding enclosure, a glove box, an enclosed conveyor system.
Do you need LEV? For most dust and fume-generating operations in small to medium workshops, the answer is yes. Elimination, substitution, and full enclosure are often not practicable for the core work process.

If LEV is the identified control, the assessment should specify what type of LEV is needed: capture hoods at each machine, flexible arm extractors, downdraft benches, on-tool extraction, or a combination.

Step 4: Review effectiveness

This is where many assessments stop too soon. Identifying that you need LEV isn't enough. You need to confirm that the LEV you have (or install) actually works.

Does the system capture contaminants effectively? Visible dust or fume escaping past the extraction point means capture is inadequate.
Is the system designed for the actual process? A system designed for one machine may not cope when you add a second extraction point. A fume arm sized for TIG welding may not handle the fume volume from MIG.
Are workers actually using it correctly? A perfectly designed system that's switched off, bypassed, or positioned wrongly doesn't control exposure.
What does the TExT report say? Your most recent thorough examination and test provides measured data on system performance. Use it.

How to Assess Whether Your Existing LEV Is Adequate

If you already have LEV installed, the risk assessment should evaluate whether it's doing its job. Here's a practical framework:

Check against the design specification. Every LEV system should have a commissioning record showing its design performance — capture velocities, air volumes, transport velocities. Compare current performance (from your latest TExT report) against these figures. A significant drop indicates degradation.

Look for visible evidence of failure. Dust settling on surfaces near extraction points. Fume visible in the worker's breathing zone. A haze in the workshop air. These are signs that the LEV isn't capturing effectively, regardless of what the last report said.

Review TExT history. Look across multiple TExT reports. Is performance steady, declining, or fluctuating? A gradual decline suggests the system is deteriorating. Fluctuating results may indicate intermittent problems — blocked filters that get cleaned just before the test, for example.

Check whether the process has changed. The LEV was designed for a specific process. If you've changed materials, increased production rates, added machines, or altered the work layout since the system was installed, the original design may no longer be adequate.

Assess the maintenance regime. A system that's poorly maintained between formal inspections will underperform regardless of its original design quality. Review your maintenance records as part of the assessment.

Consider air monitoring. Personal exposure monitoring provides objective evidence of whether the LEV is controlling exposure below the WEL. It's the most direct way to answer the question "is this LEV adequate?" The HSE's COSHH guidance covers when monitoring is required.

When You Need a New or Upgraded LEV System

Your risk assessment may conclude that the current LEV is inadequate. Common triggers for upgrading or replacing:

Exposure monitoring shows levels above the WEL despite the LEV running. The system isn't achieving adequate control.
The process has changed significantly since the system was designed — more machines, different materials, higher production rates, altered layout.
The system was never properly designed. Some LEV installations are cobbled together from available components rather than engineered for the specific process. They may never have been adequate.
The TExT examiner has flagged fundamental design problems. Not just wear-and-tear maintenance items, but issues with hood design, duct sizing, fan capacity, or system layout that can't be fixed by servicing.
You've added a new process that generates different contaminants or higher volumes than the existing system can handle.
Regulatory changes have lowered the WEL for a substance you work with (as happened with welding fume in 2019), meaning your previously adequate system no longer provides sufficient control.

In these cases, engage an LEV designer or occupational hygienist to specify what's needed. The replacement system should be designed to your specific process, not selected from a catalogue based on generic specifications.

Common Assessment Mistakes

Assessing the LEV in isolation. The LEV doesn't exist in a vacuum. It's part of a broader control strategy. Your assessment should consider how LEV interacts with work practices, housekeeping, RPE, and general ventilation. A great LEV system undermined by poor housekeeping (compressed air blowdowns, dry sweeping) still results in overexposure.

Relying on the LEV supplier's assurances. "This system is suitable for woodworking" doesn't replace your own assessment of whether it controls exposure in your specific workshop, for your specific process, to below the WEL. The employer's duty to assess cannot be delegated.

Not reassessing after changes. Your assessment is a snapshot. If you change the process, the materials, the layout, or the production volume, the assessment needs updating. A risk assessment from five years ago that predates a workshop expansion is no longer valid.

Ignoring maintenance condition. Assessing LEV adequacy based on design specifications alone ignores the reality that systems degrade. Include the actual condition and current performance data in your assessment, not just the theoretical capability.

Skipping the monitoring. For substances with low WELs — particularly carcinogens and sensitisers — personal exposure monitoring provides the only reliable evidence that controls are working. Relying on visual observation alone isn't sufficient for fine respirable dusts or fumes that are invisible at hazardous concentrations.

Documenting Your Assessment

Your COSHH risk assessment must be recorded if you employ five or more people. Even below that threshold, recording it is strongly recommended — it provides evidence of compliance and a baseline for future reviews.

The record should include:

What hazardous substances are present
Who is exposed and how
What control measures are in place (including LEV specifications)
Whether those controls are adequate, with supporting evidence
What further action is needed, with responsibilities and deadlines
The date of the assessment and when it's due for review

Review the assessment regularly — at least annually, and immediately after any significant change to processes, materials, or equipment.

Getting Started

If you haven't formally assessed your LEV, start now. Use our LEV compliance checklist generator to identify what your setup requires. Review your testing schedule to confirm your TExT dates are current. Then work through the four steps above.

LEVproof will help you keep your assessments, test records, and maintenance logs connected and audit-ready. 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
COSHH main page — HSE
Work-related lung disease — HSE
Local exhaust ventilation (LEV) guidance — 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.