The Health and Safety Executive (HSE) has recently published new research into recirculating local exhaust ventilation (Recirculating LEV) systems – equipment designed to capture dusts, mists, fumes and other airborne contaminants before they can be breathed in.
While most LEV systems discharge filtered air outside the building, some clean and return (recirculate) the air back into the workplace. This approach can save on heating costs and avoid the need for building alterations, but it comes with a critical caveat: if the filtration isn’t working properly, harmful contaminants can be reintroduced straight into the breathing zone.
The HSE’s RR1224 report looked at the selection, use and maintenance of recirculating LEV fitted with particle filters. Using industry surveys, site inspections and a workshop of experts, the study uncovered some important findings:
Not all systems are working effectively – Site inspections found examples where filters weren’t checked or replaced as recommended, even when a Thorough Examination and Test (TExT) had been completed.
Confusion over filter performance standards – There are multiple national and international filter standards, and not all duty holders understand what “thoroughly cleaned” air actually means.
Monitoring is key – The use of particle monitors and alarms can give early warning of filter failure, but not all systems have them fitted.
Maintenance matters – A regular filter inspection and replacement schedule is essential, and must follow manufacturer recommendations.
The research also identified differences across industries in how recirculating LEV is applied. Woodworking, stone working and metal fabrication are priority areas for further study, given the hazardous nature of the dusts and fumes involved.
What this means for employers
If you operate recirculating LEV, you should:
Know your filter type and efficiency rating – and the standard it was tested to.
Follow the manufacturer’s maintenance schedule – don’t wait for performance to drop before acting.
Incorporate TExT and routine visual/pressure checks – both are needed to confirm continued effectiveness.
Consider real-time particle monitoring – pressure gauges alone may not detect filter breakthrough.
Ensure staff understand the risks – provide training on why filter care is essential.
The bottom line? Recirculating LEV can be safe and effective, but only if designed, maintained and monitored correctly. Without this, you could be creating the very hazard you’re trying to remove.
You can read the full HSE research report here: RR1224 – The selection, use, and maintenance of recirculation LEV.
