Analysis of VOCs in hyperbaric atmospheres
This purpose of this investigation was to develop a methods for the determination of trace level VOCs present in offshore hyperbaric diving environments using Thermal Desorption Gas Chromatography-Mass Spectrometry. As the hyperbaric chambers would usually be onboard a ship, the sampling and transportation of samples would be in cylinders rather than canisters or sorbent tubes. The sensitivity of the method had to be greater than methods for normobaric occupational exposure, as a chamber pressure was typically ten times normal atmospheric pressure and the divers were continuously exposed to all the VOCs present in the atmosphere. To reduce background contamination, cleaning procedures were put in place for both Tenax tubes and sampling cylinders. The performance of the Tenax tubes, the recovery from cylinders and GC-MS were investigated systematically using standards, CRM and environmental samples. This ensured that results determined were both qualitative and quantitative. The cylinder sampling experiments had shown that electropolished cylinders were quantitative for all types of trace VOC gas mixtures, while the Teflon lined and sand-blasted cyclinders showed reasonable recoveries for humid samples, like those of hyperbaric but low recoveries for dry gas mixtures. The VOC concentrations present in hyperbaric atmospheres were typically ten times those found in normobaric work environments, in the range of 50 - 300 mg/m3 for living chambers. Many compounds had been detected, including benzene, toluene, substituted aromatics, alkanes, chloroform, trichloroethylene and even compounds like pinene or limonene. In general all locations showed levels well below their HOELs or OELs. The method was also adapted to determine VOCs present in atmospheres by Tenax tube diffusive sampling. These experiments showed clearly that the method could be used for detection of VOCs in occupational environments and also urban air environments if required.