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RR982 - Real time measurement of dichloromethane containing mixtures

Dichloromethane (DCM), also known as methylene chloride, is typically used as a component of proprietary paint strippers. Occasional workplace fatalities result from its use in GB. The aim of this project was to determine the suitability of commercial, real-time (direct-reading), portable gas detectors to monitor DCM in the presence of other volatile organic compounds typically found in paint strippers. Various types of gas detector (based on photoionisation, infrared and catalytic sensors) were exposed to air mixtures of DCM, methanol and isopropanol.

It was found that high sensitivity photoionisation detectors (PIDs) with high energy UV lamps are approximately 30 times more sensitive than PIDs with low energy UV lamps. Both PIDs can measure DCM at levels below the Workplace Exposure Level (WEL) of 300 ppm (15 minute short-term). They are both cross-sensitive to the other VOCs investigated. However, this may still allow reasonably accurate measurement of DCM, as the concentration of DCM in the vapour phase is typically much greater than the other VOCs. The other types of detector were not suitable for measurement of DCM around and below the WEL.

The high sensitivity PIDs were found to lose sensitivity quite rapidly and do not have a long shelf life when compared to the low sensitivity PIDs. Nevertheless, with care, they can be used to measure low (ppm) levels of DCM. Further work is required to evaluate the effect of hydrogen fluoride, another component of paint strippers, on the performance of PIDs.

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Updated 2019-09-03