The Health Case Behind LEV Testing Intervals

What the interval is built on

The fourteen-month figure comes from Regulation 9 of the Control of Substances Hazardous to Health Regulations (COSHH), which requires most local exhaust ventilation to undergo a thorough examination and test - often shortened to TExT - at least once every fourteen months. That number is not arbitrary, and it is not generous by accident. It sits two months beyond an annual cycle so that a system tested once a year never quietly slips past its legal maximum because of a scheduling clash. In other words, the law already assumes you are aiming for roughly twelve months and gives you a small buffer, not permission to stretch to fourteen as a matter of routine.

The detail behind that headline lives in HSG258, the HSE guidance titled Controlling airborne contaminants at work: a guide to local exhaust ventilation. It is the reference document a competent examiner works to, and it treats fourteen months as an outer limit rather than a universal answer. Where a process is more hazardous, or where wear and tear would be expected to degrade capture between visits, the interval should come down. COSHH Schedule 4 spells this out for a handful of named high-risk processes, setting intervals as short as one month or six months. A commercial kitchen is not usually on that list, but the principle behind it - match the interval to the risk - is exactly what should shape your own schedule.

This is where the health case and the compliance case stop being separate things. LEV testing is a legal duty, and the duty sits with the employer as the person in control of the workplace, not with the contractor or the equipment supplier. If you want the full picture of where that obligation comes from and who it lands on, we set it out in detail in our guide on whether LEV testing is a legal requirement. But the reason the duty exists is protective. A thorough examination is not a tick in a box - it is a structured check that the system still captures contaminant at source, still moves enough air at the hood face, still filters what it should and still discharges cleanly. When any of those fails, the people at the stove are the ones who find out, usually slowly and usually too late.

Consider how a kitchen canopy degrades. On the day it was commissioned, it was designed to pull contaminated air away from the cook before it reached their breathing zone. Grease then does what grease does. It builds on the filters, narrows the extract, coats the impeller and drags the fan away from its design duty. None of this announces itself. The extraction still hums, the canopy still looks the part, and the air above the range still appears to clear. But capture velocity - the speed of air at the point where fume is generated - can fall well below the level needed to actually draw contaminant in. The staff notice nothing except, perhaps, a warmer and stickier kitchen. Their exposure, meanwhile, has crept up. A test caught early flags that drift while it is still cheap to fix. A test left to the last legal day may certify a system that has been underperforming for months.

That gradual, invisible failure is the whole argument for treating the interval seriously. The pollutants a kitchen produces are not the kind that make you cough and leave. Ultrafine particles and fine particulate matter deposit deep in the lung and drive oxidative stress and inflammation. Aldehydes irritate the airway lining. Repeated across shifts, weeks and years, that low-grade exposure is exactly the pattern that produces occupational asthma, reduced lung function and chronic respiratory disease - conditions that rarely trace back to a single bad day. Good extraction, proven at a sensible interval, is what keeps that dose low enough to matter less.

There is also a record to think about, and it is more than bureaucracy. Examination reports must be kept for at least five years, and read as a series they tell a story your logbook alone cannot - whether performance is holding steady or sliding, whether a particular canopy needs attention sooner, whether the interval you have chosen is actually right for the way the kitchen is used. A single certificate proves a moment. A run of them proves a trend, and a trend is what lets you set an interval on evidence rather than habit.

So the practical answer to "how often" is rarely just fourteen months. For a light-use servery it might genuinely be the maximum. For a high-output kitchen running gas chargrills through long services, the honest interval is often shorter, because that is what the risk and the degradation rate demand. The number on the certificate should be the output of a judgement about exposure, not a default copied from the last engineer. Setting it that way is the difference between a system you hope is working and one you can show is protecting the people who rely on it.