Ventilation Assessment
Services · Services overview
A workplace ventilation assessment is a structured engineering review of how a building's ventilation actually performs against what the work being carried out requires. It looks at airflow, sources of contamination, work patterns, system condition and indoor air quality together, and gives the duty-holder a clear, prioritised picture of where the ventilation is adequate, where it is borderline, and where it needs intervention.
What a workplace ventilation assessment is
Ventilation assessments sit one level above routine LEV testing. Where an LEV TExT examines a specific extraction system against its design benchmark, a ventilation assessment examines the whole ventilation strategy of a workspace and asks whether it is the right strategy for the activity, the building and the people working in it.
The output is a written report covering airflow measurements, capture and dilution performance, indoor air quality indicators, observations of how work is done in practice, and a prioritised list of improvement actions. It is the document that helps managers, engineers and safety teams make informed decisions about where to invest, what to monitor and what to fix first.
When an assessment is needed
There is no single statutory interval for a ventilation assessment, but several trigger points make one the right next step:
- Process or substance change — new materials, new equipment, increased throughput or modified workflows.
- Building change — extensions, partitioning, new mezzanines, relocated fresh-air intakes or discharge points.
- Operator concerns — reports of symptoms, visible dust or fume, persistent odours or thermal discomfort.
- Compliance triggers — upcoming LEV TExT, HSE inspection follow-up, insurance audit, or new COSHH assessment.
- Performance triggers — failed or borderline LEV results, escalating filter maintenance, or unexplained energy use.
- Capital planning — feasibility for a new line, factory extension or retrofit, where understanding the current ventilation envelope matters.
What is reviewed during an assessment
A competent assessment is multi-layered. Each layer addresses a different aspect of how the ventilation is performing and how it is being used.
- Airflow — supply and extract volumes by zone, room air change rates, and pressure relationships between zones.
- Sources — where airborne contaminants are released, in what form, at what rate, and how those releases interact with the room airflow.
- Work patterns — how operators move, where they stand, how long they spend in higher-emission tasks, and whether ventilation provision matches reality.
- System condition — hoods, ductwork, dampers, filters, fans and discharge points, including how well they have been maintained.
- Extraction performance — capture velocity, face velocity and transport velocity for any LEV in the assessed area.
- Room air movement — short-circuiting between supply and extract, dead zones, and unintended airflow from doors, gates and process equipment.
- Indoor air quality indicators — CO₂, respirable and inhalable particulate, VOC totals and thermal comfort metrics where relevant.
- Odours and contaminant escape — visible escape, complaints, and the locations where escape concentrates.
Assessment versus LEV TExT
A statutory LEV TExT under HSG258 is required to verify that an installed local exhaust ventilation system is performing against its commissioned benchmarks. It is hood-by-hood, instrument-led and compliance-focused.
A ventilation assessment is broader. It includes the same instrument measurements where they are relevant, but it also takes a step back to ask whether the chosen ventilation strategy is the right one for the current process. A failing LEV TExT often prompts a ventilation assessment to decide whether the answer is repair, redesign or a fundamentally different control approach.
Practical outputs of an assessment
The assessment report should leave the duty-holder with three things: a clear picture of current performance, a clear picture of where it is falling short, and a clear set of options for putting it right.
Findings are typically grouped by zone or process and graded by risk. Recommended actions are prioritised — immediate, short-term, planned — with an indication of the expected outcome and, where useful, an outline of the engineering options. The aim is to give managers enough to make a decision without having to re-do the engineering thinking themselves.
What good looks like
A useful ventilation assessment is unambiguous about both the verdict and the next step. It names the zones examined, the parameters measured, the benchmark applied, the verdict and the action. It avoids generic recommendations and resists the temptation to default to 'install more extraction' when the underlying issue is a process or hood-position problem.
Where the assessment identifies that the current ventilation is adequate, it should say so plainly. Reports written to find faults are no more useful than reports written to confirm what is already in place — both undermine the duty-holder's ability to act with confidence.
Frequently asked questions
Is a ventilation assessment a legal requirement?
There is no single statutory requirement to carry out a ventilation assessment by name, but COSHH risk assessment, the Workplace (Health, Safety and Welfare) Regulations and HSG258 all rely on an underlying understanding of how the workspace's ventilation actually performs. A formal assessment is the most defensible way to develop and document that understanding.
How is a ventilation assessment different from a LEV test?
An LEV test verifies the performance of a specific extraction system against its commissioned benchmarks. A ventilation assessment is broader — it covers room airflow, indoor air quality, work patterns and system condition together, and judges whether the overall ventilation strategy is appropriate for the process being done.
How long does a ventilation assessment take?
It depends on the size and complexity of the site. A single production hall with one or two extraction systems can usually be assessed in a day on site plus follow-up reporting. A large multi-zone manufacturing site with multiple LEV systems and process areas will take longer and may be staged.
What documentation should we provide for an assessment?
Existing COSHH risk assessments, the LEV user manual and previous TExT reports, any commissioning data for ventilation equipment, recent process or layout changes, and any operator concerns or symptom reports are all useful. Where documentation is missing, the assessor will reconstruct what is needed from the system as found.
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