Acid LEV Testing
Ventilation & Controls · Ventilation & Controls overview
Acid LEV testing is the statutory Thorough Examination and Test of local exhaust ventilation that captures acid mists, alkaline aerosols and corrosive fumes at source. Under regulation 9 of the Control of Substances Hazardous to Health (COSHH) Regulations 2002 every LEV system controlling exposure to a hazardous substance must be examined and tested at least every 14 months, and more often for high-hazard chemistries. For acid and corrosive duty, that examination is a specialised exercise — the hoods, ducting, fans and discharge are all in chemically aggressive service, and the test must demonstrate that capture, containment and exhaust are still controlling exposure at the operator's breathing zone.
Where acid LEV is used
Acid LEV is the primary engineering control wherever an open acid or alkaline process is operated. The most common UK applications are electroplating and anodising lines, pickling and passivation tanks, battery formation and electrolyte filling, semiconductor wet benches, laboratory acid digestion, and chemical reactors that vent acid vapour during charging or sampling. In each case the LEV is what stands between the operator and a substance with an EH40 Workplace Exposure Limit measured in fractions of a milligram per cubic metre.
The dominant LEV configurations on acid duty are lip extraction along the long edges of plating and pickling tanks, push-pull systems on wider tanks where lip extraction alone cannot reach the centre, partial enclosures with acid-rated extract on wet benches and acid mixing stations, and fume cupboards on laboratory acid work. Each configuration has a different test signature, and the LEV report has to reflect the actual design.
- Lip and slot extraction on plating, anodising and pickling tanks.
- Push-pull systems on wide chrome, sulphuric and nitric tanks.
- Acid wet benches and partial enclosures with corrosive extract.
- Fume cupboards on laboratory acid digestion and HF work.
- Acid mixing, dosing and electrolyte filling stations.
- Acid storage vent extraction and bunded transfer points.
What an acid LEV thorough examination covers
The HSE guidance in HSG258 sets out the framework for an LEV Thorough Examination and Test, and acid LEV is examined against the same three questions: is the system in good working order, is it still controlling exposure as designed, and is the user operating and maintaining it correctly. On acid duty the engineer also has to make a judgement on the corrosion state of the system — pitted ducting, perished gaskets, blocked drains and failing scrubber media all degrade capture before the airflow numbers change.
The visual and condition assessment looks at hood geometry against the original commissioning intent, ducting material and condition, dampers, flexible connections, fan housing and impeller, scrubber or mist eliminator, and the discharge point. The performance measurements record face velocities at the hood, capture velocities in the operator's working position, static pressures at defined test points, airflow volumes, and where appropriate the dust- and mist-laden plume behaviour with smoke.
Capture and containment on acid systems
Capture velocity is the airflow the hood must generate in the working position to entrain the contaminant cloud and pull it into the hood. For acid mist released by gassing electrolysis or by hot acid pickling, the practical capture velocity at the bath edge is in the range of 0.5–1.0 m/s, and the LEV test demonstrates that velocity is still achieved across the working length of the tank.
Containment is the second control. Push-pull systems and partial enclosures are tested by smoke and tracer to show that the acid plume is held inside the hood envelope under realistic disturbances — operator movement, cross-draughts from doors, forklift passes and adjacent extraction. A system that achieves the airflow numbers but loses containment under real conditions is not adequately controlling exposure.
Material compatibility and corrosion
Acid LEV is corrosive duty from hood to stack. Hoods, ducting, dampers, fan casing and any wetted instrumentation have to be specified for the chemistry — typically polypropylene or FRP for sulphuric, hydrochloric and nitric mists, with PVDF for HF and hot nitric. The Thorough Examination records the condition of each component, flags any incompatible repairs (mild steel patches, unsuitable sealant, ferrous fixings inside the airstream) and recommends remediation before the next test.
Drain points, scrubber media and mist eliminator pads are inspected and, where they have reached the end of service life, the report makes a defined recommendation rather than passing the system on numbers alone.
Linking LEV evidence to personal exposure
A passing LEV test is necessary but not sufficient. The COSHH judgement on whether acid exposure is adequately controlled is made on personal monitoring evidence at the operator's breathing zone against the EH40 limit. The LEV report and the personal monitoring report are two halves of the same control case, and the most defensible UK acid sites keep them on the same review cycle.
Where personal sampling shows borderline or non-compliant exposure, the LEV test is the first place to look — typically reduced capture velocity, lost containment, scrubber breakthrough, or a change in process that the LEV was not designed for.
When to test acid LEV
The statutory maximum interval is 14 months. In practice acid LEV is tested annually to keep the cycle inside the legal limit, and high-hazard chemistries (chromium VI, HF, fuming nitric, chlorine) are tested at six-monthly intervals or after every campaign. Re-test is also triggered by any modification, a change of chemistry, a change of process throughput, a scrubber media change, operator symptoms or an enforcement or insurer audit.
Frequently asked questions
How often does acid LEV need to be tested?
At least every 14 months under COSHH regulation 9. Most UK acid sites work to a 12-month cycle, and high-hazard chemistries (chromium VI, HF, fuming nitric) are tested more frequently.
Does an LEV test prove acid exposure is controlled?
It is half the case. LEV testing shows the engineering controls are still working as designed; personal monitoring at the breathing zone against the EH40 limit shows the operator is actually controlled. Both are required for a defensible COSHH judgement.
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