HSG258 Explained: The LEV Guidance in Brief

The LEV lifecycle

HSG258 in seven plain steps

1. Understand the contaminant first. Before any hood is bolted up, HSG258 wants you to know what you are trying to capture - the substance, how much of it there is, and how it behaves in the air. A fine, buoyant fume drifts very differently from a heavy grinding dust, and the whole design flows from getting this right.
2. Design for the cloud, not the room. The guidance is built around the idea of the contaminant cloud and capturing it at source before anyone can breathe it in. It classifies hoods and stresses that a hood placed close to the process, in the path of the cloud, will always beat a distant one fighting against draughts and cross-flows.
3. Commission and benchmark the system. When the system is installed it must be commissioned - proven to work and measured while it is doing so. Those first readings become your benchmark data, the numbers every future test is compared against. Without them, a later examiner has nothing to judge current performance by.
4. Give the user a logbook and clear checks. HSG258 expects the people operating the system to know what good looks like. That means a user manual, a logbook, and simple daily or weekly checks - a gauge reading here, a visual look at a filter there - so faults are caught early rather than months down the line.
5. Maintain it to a plan. Extraction wears, clogs and drifts out of tune. The guidance asks for planned, preventive maintenance rather than waiting for a breakdown, because a system that has quietly lost half its airflow can look perfectly fine from across the workshop.
6. Have it thoroughly examined and tested. This is the step most people know as LEV testing, and its proper name is the Thorough Examination and Test, or TExT. A competent person inspects the whole system, measures airflow against your commissioning data, checks hoods, ducts and filters, and issues a written report saying whether it still controls exposure - or where it falls short.
7. Keep the records. The report is not paperwork for its own sake. COSHH requires you to keep these records for at least five years, so you can show a clear, unbroken history of a system that has been kept in effective working order.

The rule everyone asks about

Where the 14-month figure comes from

The one number that follows HSG258 around is fourteen months. It does not come from the guidance itself but from COSHH Regulation 9, which requires most LEV systems to have a Thorough Examination and Test at least once every fourteen months. The odd figure exists on purpose - fourteen rather than twelve lets a business hold the test in the same working period each year without the date slowly creeping forward until it is overdue.

Fourteen months is a maximum, not a target, and it is not the interval for everyone. Certain higher-risk processes listed in COSHH Schedule 4 must be examined far more often - as frequently as every six months, and in some cases every month. These are the jobs with the most serious health links, and the shorter interval reflects how much is at stake if the extraction underperforms even briefly. If you are unsure which bracket a process falls into, that judgement is part of what a competent examiner brings.

It helps to see where LEV sits in the bigger picture. Extraction is an engineering control, which means it comes fairly low down the ranking of ways to manage a hazardous substance - you are expected to design the risk out or swap the substance first, and only then reach for equipment that captures what remains. That ranking is worth understanding in its own right, and we set it out in our guide to the hierarchy of control. HSG258 also does not stand alone - it is the practical partner to your wider COSHH duties, and the decision to fit LEV at all should fall out of a proper assessment, which is the ground covered in how COSHH assessments should actually be done.

The thread running through the whole document is honest evidence. A system that captures the cloud, benchmarked when new, checked by its users, maintained to a plan and tested on time gives you something an inspector can trust and, far more importantly, keeps your people breathing clean air.