Evaluation of flow controllers used with evacuated canisters to assess VOC exposures in occupational and non-occupational environments

Abstract

Ideally, measuring exposures to volatile organic compounds should allow for modifying sampling duration without loss in sensitivity. Traditional sorbent-based sampling can vary sampling duration, but sensitivity may be affected when capturing shorter tasks. Diaphragm and capillary flow controllers allow for a range of flow rates and sampling durations for air sampling with evacuated canisters. The goal of this study was to evaluate the extent to which commercialized capillary flow controllers satisfy the bias (±10%) and accuracy (±25%) criteria for air sampling methods as established by the National Institute for Occupational Safety and Health (NIOSH) using the framework of ASTM D6246 Standard Practice for Evaluating the Performance of Diffusive Samplers to compare their performance with diaphragm flow controllers in a long-term field study. Phase 1 consisted of a series of laboratory tests to evaluate capillary flow controller flow rates with respect to variations in temperature (−15–24 °C). The results demonstrated a slight increase in flow rate with lower temperatures. In Phase 2, the capillary flow controller was evaluated utilizing a matrix of parameters, including time-weighted average concentration, peak concentration (50–100× base concentration), air velocity across the sampler inlet (0.41–0.5 m/s), relative humidity (20–80%), and temperature (10–32 °C). Comparison of challenge concentrations with reference concentrations revealed the aggregate bias and overall accuracy for four tested compounds to be within the range of criteria for both NIOSH and ASTM standards. Additionally, capillary flow controllers displayed lower variability in flow rate and measured concentration (RSD: 2.4% and 4.3%, respectively) when compared with diaphragm flow controllers (RSD: 6.9% and 7.2%, respectively) for 24-hr laboratory tests. Phase 3 involved further testing of flow rate variability for both diaphragm and capillary flow controllers in a field study. The capillary flow controller displayed a lower level of variability (RSD: 5.2%) than the diaphragm flow controller (RSD: 8.0%) with respect to flow rate, while allowing for longer durations of sampling.

Keywords:

• Air sampling
• bias
• capillary flow controller
• diaphragm flow controller
• diffusive sampling
• sensitivity

Acknowledgments

The authors would like to acknowledge the following research assistants who participated in portions of this study: Victoria Goudreau, Benjamin Stone, and Emily Sullivan.

Disclaimer

The findings and conclusions in this report are those of the author(s) and do not necessarily represent the official position of the National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention. Mention of any company or product does not constitute endorsement by the National Institute for Occupational Safety and Health. In addition, citations to websites external to NIOSH do not constitute NIOSH endorsement of the sponsoring organizations or their programs or products. Furthermore, NIOSH is not responsible for the content of these websites. All web addresses referenced in this document were accessible as of the publication date.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availablilty statement

The data that support the findings of this study are available from the corresponding author, upon reasonable request.

Additional information

Funding

This work was partially funded by the Environmental Security Technology Certification Program (ESTCP), Project number: ER-201504. ESTCP is the Department of Defense’s environmental technology demonstration and validation program.