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LEV testing - monitoring
An LEV test tells you the extraction is working. It does not tell you how much of a substance a worker is actually breathing. For that you need air sampling - and knowing when you need it is part of controlling exposure properly.
The short answer
A thorough examination and test confirms the LEV is controlling contaminant at source. Air sampling - exposure monitoring - measures how much of a substance is actually in the air a worker breathes, against workplace exposure limits. It is needed when the LEV test alone cannot answer whether exposure is adequately controlled: high-risk substances, uncertain control, a legal duty to monitor, or a system whose performance is in doubt.
Two different questions
LEV testing and air sampling answer different questions. The thorough examination and test looks at the equipment - is the hood capturing, is the airflow adequate, is the control working at the point of release. Air sampling looks at the person - how much of the substance is actually present in their breathing zone over a working period, expressed as a dose that can be compared to a limit.
A system can pass its LEV test and a worker can still be over-exposed - through a task the hood does not fully cover, a source outside the capture zone, or a substance so hazardous that even good capture leaves a residual worth measuring. The test says the control works; sampling says whether the person is actually protected. Sometimes you need both to be sure.
When it is needed
Air sampling comes into play in a few situations. Where the substance is particularly hazardous and the consequences of over-exposure are severe, measuring actual exposure gives assurance that capture alone cannot. Where there is genuine doubt about whether control is adequate - a marginal system, an awkward task, a complaint or symptom - sampling settles it with a figure. And where the risk assessment or the law calls for exposure monitoring as a duty in its own right, it has to be done regardless.
COSHH itself requires exposure monitoring in certain circumstances - where it is needed to ensure control is adequate, or for specified substances and processes. In those cases air sampling is not an optional extra to the LEV test; it is a separate legal obligation that the test does not discharge.
What sampling measures
Air sampling measures the concentration of a substance in the air a worker breathes, typically over a representative period, using recognised methods. The result is compared against the relevant workplace exposure limit - the level below which exposure is considered adequately controlled for that substance. Personal sampling, worn by the worker, captures what they actually breathe; static sampling measures the general area.
The output is a number with real meaning: an exposure figure set against a limit, showing whether a worker is protected or not. That is something an LEV test, which measures the equipment rather than the person, cannot provide - which is why the two are complementary rather than interchangeable.
How they work together
In practice the two fit together. The LEV keeps exposure down by capturing contaminant at source; the thorough examination and test confirms the LEV is doing that; and air sampling, where it is needed, verifies that the resulting exposure is actually within safe limits. Each layer checks a different thing, and together they give a complete picture of whether people are protected.
Sampling can also feed back into the LEV. A result showing exposure creeping towards a limit is a prompt to look hard at the control, even if it recently passed its test - the equipment may be adequate on paper but not enough for the task in practice. The two readings inform one another.
Deciding for your site
Whether you need air sampling is a question for your COSHH risk assessment, not a default add-on to every LEV test. Most lower-risk, well-controlled situations are adequately handled by good LEV and its thorough examination and test. Sampling is called for where the hazard, the doubt or the law makes measuring actual exposure necessary.
The practical approach is to treat LEV testing as the routine baseline and air sampling as the targeted tool for the situations that need it. Where your risk assessment identifies one of those situations, sampling is how you close the gap between knowing the control works and knowing the worker is safe.
Questions
Exposure monitoring that measures how much of a substance is actually in the air a worker breathes, compared against a workplace exposure limit - as opposed to an LEV test, which checks the extraction equipment is controlling contaminant at source.
Where the substance is particularly hazardous, where there is genuine doubt about whether control is adequate, or where the COSHH risk assessment or the law requires exposure monitoring as a duty in its own right.
Not necessarily. A system can pass its test while a worker is still over-exposed through a task the hood does not fully cover. Where the risk calls for it, sampling is a separate check the test does not replace.
The relevant workplace exposure limit for the substance - the level below which exposure is considered adequately controlled. Personal sampling worn by the worker captures what they actually breathe.
COSHH requires it in certain circumstances - where it is needed to ensure control is adequate, or for specified substances and processes. In those cases it is a separate obligation, not an optional extra to the LEV test.
The LEV controls exposure, the test confirms the LEV works, and sampling verifies the resulting exposure is within safe limits. Each checks a different thing, giving a complete picture of protection.
We test your LEV to COSHH and HSG258 and advise where exposure monitoring is needed alongside it.
