Monitoring & metering
An introduction to sampling for vapours
in this article, adeel Hassan, technical product manager at Casella, discusses the importance of employers across industrial sectors monitoring for exposure of harmful dusts, gases and vapours, in order to meet the requirements of the CosHH regulations. Hassan provides an in-depth introduction to sampling for vapours, measuring exposure, sampling media and calibration
M
anufacturing processes found across many industrial sectors have the potential to expose workers to harmful
dusts, gases and vapours and as a consequence, UK employers must meet the requirements of the CoSHH Regulations and in the US, the Code of Federal Regulations (CFR). Similar legislation exists worldwide, the common theme being an onus on hazard identification, risk assessment and the provision of appropriate control measures. Volatile organic compounds (VOCs) (some of
which are hydrocarbons) are common hazards found in the chemical, pharmaceutical and oil and gas industries, typically released through process leaks but also routinely during plant maintenance. There are a raft of other hazardous chemicals found in diverse manufacturing subsectors ranging from fabricated metal to textiles and furniture but also painting and printing. VOCs in particular have a significant vapour pressure at normal ambient temperature which means they evaporate (volatilise) at low temperatures and can easily enter the body through normal breathing, so monitoring the workplace air is vitally important. Indeed, if exposure or failure of control measures could lead to exposure limits being breached then exposure monitoring is expressly required. High chemical concentrations can pose an
immediate (acute) risk to life but repeated exposure to relatively low concentrations can lead to long term (chronic) illnesses, cancers and even hearing loss in the case of ototoxic chemicals such as solvents, nitriles, metals and their compounds.
Measuring exposure A direct reading instrument is often used, for detecting single or multiple hazardous gasses where there is an acute risk but this does not
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Flow pumps can be clipped onto a belt or worn in a pocket
August 2019 Instrumentation Monthly
account for low level exposures which may vary throughout the workspace and/or with time. There are basically three ways of sampling gases
or vapours for subsequent laboratory analysis: - By collecting a small amount of the workplace
atmosphere in a suitable airtight container By drawing air through a solution in a
1 2
bubbler or impinger where the contaminant reacts with the liquid
3 By allowing workplace air to pass through an
adsorbent material. Static sampling will generally lead to an
underestimate of personal exposure but may be useful when examining the effectiveness of control measures, to identify sources or monitor known ‘hotspots’ in process plant. Personal monitoring is a preferred solution whereby a long-term average concentration may be determined and the use of
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