Sampling methods used for the assessment of exposure to volatile organic chemicals (VOCs) in the workplace or for environmental studies are now limited to an upper integrative sampling time of 24 hours or less. Generally, these methods lack versatility and are difficult to use. A passive sampler that can extend sampling periods was developed as part of this research. This novel sampler relies on capillary tubes to restrict and control ambient air entry into an evacuated sample container. / A mathematical model was derived by modifications to the Hagen-Poiseuille and ideal gas laws. This model defines the relationship between container volume and capillary geometry (length/internal diameter) required to provide selected sampling times. Based on theoretical considerations, simulations were performed to study the effects of dimensional parameters. From these results, capillaries having 0.05 and 0.10 mm internal diameters were selected according to their ability to reduce sampling flow rates and to increase sampling times. Different capillary lengths were tested on various sampler prototypes. It was found that a constant sampling flow rate was delivered when a maximum discharge rate was established under the influence of a pressure gradient between a vacuum and ambient pressure. Experimental flow rates from 0.018 to 2.6 ml/min were obtained and compared with model predictions. From this comparison, empirical relationships between capillary geometry and maximum discharge rate given by the pressure gradient were defined. Essentially, based on these empirical relationships, capillary sampling flow controller specifications can be calculated to offer extended integrated sampling periods. On this basis, sampler prototypes were configured for stationary sampling and personal sampling. / Studies, based on theory, have indicated that factors such as temperature, humidity and longitudinal molecular diffusion are not likely to influence the passive sampling process. Subsequent experiments confirmed that temperature changes should not significantly affect flow rates delivered by controllers, and that molecular diffusion does not have any impact on the representativeness of long-term samples. Recovery tests provided acceptable results demonstrating that selected capillaries do not contribute to adsorption that could seriously affect the validity of this sampling approach. / Field demonstration studies were performed with both stationary and personal sampler prototypes in the indoor and outdoor environments. The performance of the sampler compared favorably, and in some instances, exceeded that of accepted methodology. These novel samplers were more reliable, had greater versatility and principally, allowed sampling periods extending from hours to a month. These inherent qualities will assist industrial hygienists and environmentalists in the study of emission sources, pollutant concentrations, dispersion, migration and control measures. This novel sampler is presently the only device available for the effective study of episodic events of VOC emission. / Selected capillary geometries acting as a restriction to the entry of ambient air into evacuated sample container can provide a simple, versatile and reliable alternative for the collection of VOCs. This approach can contribute to a better understanding of VOC effects on human health and the environment.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.34455 |
| Date | January 1997 |
| Creators | Simon, Philippe, 1964- |
| Contributors | Farant, Jean-Pierre (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Occupational Health.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001559065, proquestno: NQ30387, Theses scanned by UMI/ProQuest. |
Page generated in 0.0019 seconds