Acid Air Sampling
Acid Mist · Acid Mist overview
Acid air sampling is the practical measurement step behind any COSHH acid mist assessment. Personal pumped sampling draws workplace air through a medium selected for the target acid, and the laboratory result is compared with the relevant EH40 Workplace Exposure Limit.
Sampling methods used for acid mists and vapours
The right sampling medium depends on the acid and the phase it exists in. Sulphuric acid mist is typically collected on a treated filter and analysed for sulphate. Hydrochloric and nitric acids exist as both gas and aerosol, and are collected on sorbent tubes, impregnated filters or denuders that capture both phases. Chromic acid mist is collected as Cr(VI) on a PVC filter following HSE MDHS-style methodology.
Sampling pumps run at the flow rate validated for each method, with calibration before and after the sample. Sampling heads are clipped within the operator's breathing zone — typically within 300 mm of the nose and mouth — so the measured concentration reflects what the operator actually inhales.
Personal versus static sampling
Personal sampling is the basis for comparison with EH40 WELs because exposure depends on where the operator stands, how often they lean over the tank, and which tasks they carry out. Static (area) samples are useful for characterising mist drift across a plating shop or pickling line, but they do not replace personal sampling for the operator's exposure judgement.
Sampling strategy under BS EN 689
Sample numbers per similar exposure group are set against the BS EN 689 framework. For each group the strategy considers both the 8-hour TWA and any short-term (15-minute) WEL, so peak exposures at tank-side are not hidden inside a quiet shift average.
Analysis and reporting
Samples are analysed in a UKAS-accredited laboratory, most often by ion chromatography, and reported in mg/m³ against the appropriate EH40 limit. A defensible report records the sampling method reference, flow rate, sample duration, blank result, limit of detection and the operating condition during sampling, so the result can be defended in an HSE review.
Frequently asked questions
Can one sampling visit cover several acids?
Yes — multiple media can be run in parallel on the same operator to cover different acids, provided each method is selected for the chemistry in use. The sampling plan must record which medium relates to which acid.
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