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LEV testing - guidance
HSG258 is the document every proper LEV test is carried out to - but few people outside the trade have read it. Here is what it is, what it covers, and why it is the reference point for whether your extraction is doing its job.
The short answer
HSG258, Controlling airborne contaminants at work, is the Health and Safety Executive's guidance on using local exhaust ventilation to control dust, fume, mist and vapour. It covers an LEV system's whole life - designing it to control exposure, commissioning it, and thoroughly examining and testing it in service. It is guidance rather than law, but it is the recognised benchmark for how LEV should be designed and tested to meet the COSHH duty.
What it is
HSG258 is a Health and Safety Executive guidance document - its full title is Controlling airborne contaminants at work: A guide to local exhaust ventilation. It is not itself a regulation; the legal duty comes from COSHH, which requires you to control exposure and to maintain, examine and test the LEV that does it. HSG258 is the practical guide to how to meet that duty well.
Because it is the recognised guidance, it functions as the benchmark. When a thorough examination and test is described as carried out to HSG258, it means the examination followed the method the HSE sets out - which is what gives the result its authority with inspectors, insurers and risk assessors.
Design and commissioning
A common misunderstanding is that HSG258 is only about testing. In fact it covers the whole life of an LEV system, starting with design: capturing contaminant at source, choosing the right hood, providing adequate capture velocity, and sizing the ductwork and fan as a balanced system. Get those right and the system controls exposure; get them wrong and no amount of testing will fix it.
It also covers commissioning - establishing, when the system is installed, a benchmark of how it performs when working correctly. That benchmark is what every later examination is compared against. HSG258 treats design, commissioning and testing as one continuous story, because a system that passes is one that was built to control exposure in the first place.
The three-stage test
The part most people meet is the thorough examination and test, and HSG258 structures it in three stages. First, a thorough visual examination of the system's condition and integrity - hoods, ducting, filters, fan, discharge and indicators. Second, measurement of technical performance, such as face velocity and capture at each hood, to check the system is actually controlling exposure. Third, an assessment of whether that control is adequate for the people using it.
Those three stages are why a proper LEV test is more than a quick airflow reading. HSG258 requires the examiner to look at condition, measure performance, and judge control - and to produce a report saying, with figures, whether each part of the system is doing its job. A test that skips stages is not to HSG258, whatever it is called.
What it means for duty holders
You do not need to read HSG258 cover to cover to benefit from it. What matters for a duty holder is knowing that it exists, that it is the standard your LEV should be designed and tested to, and that a competent examiner works to it. When you ask whether a test was carried out to HSG258, you are asking whether it followed the recognised method - which is the difference between a defensible examination and a superficial one.
It is also useful context for the whole COSHH picture. HSG258 explains why capture at source matters, why commissioning gives a baseline, and why testing has to measure control rather than just airflow. That understanding helps you commission systems and tests that will actually protect people and stand up to scrutiny.
Where it fits
HSG258 sits alongside the broader COSHH duties rather than replacing them. COSHH requires the risk assessment, the control of exposure, the maintenance and testing of controls, and where needed monitoring and health surveillance. HSG258 is the detailed how-to for the LEV part of that - the design, commissioning and examination of the extraction that does the controlling.
So the useful way to place it is as the technical reference for getting LEV right, within the legal framework of COSHH. Meet the COSHH duty by controlling exposure; use HSG258 to make sure the LEV that achieves it is properly designed, commissioned and tested. Together they are how good extraction actually protects people.
Questions
The HSE guidance Controlling airborne contaminants at work, covering the use of local exhaust ventilation to control dust, fume, mist and vapour - including design, commissioning and the thorough examination and test of LEV systems.
No. It is HSE guidance. The legal duty comes from COSHH, which requires you to control exposure and to maintain, examine and test the LEV. HSG258 is the recognised guide to how to meet that duty.
No. It covers an LEV system's whole life - designing it to capture at source, commissioning it to establish a performance benchmark, and examining and testing it in service.
A visual examination of the system's condition, measurement of technical performance such as face velocity and capture, and an assessment of whether the control is adequate for the people using it.
Because it means the examination followed the HSE's recognised method - condition, performance and control - which is what gives the result authority with inspectors, insurers and risk assessors.
COSHH sets the legal duties; HSG258 is the detailed how-to for the LEV part - the design, commissioning and examination of the extraction that controls exposure.
We examine and test to HSG258 and advise at design and commissioning, so your extraction is proven the way the guidance sets out.
