Evaluation of Sampling Bias During VOC Exposures Involving Peaks Using Capillary Flow Controllers Coupled with Evacuated Canisters

Details

• Personal Author:
  LeBouf, Ryan F.
• Description:
  Objective: NIOSH is in the process of evaluating canister methods for sampling of a wide range of VOCs. Capillary flow controllers have a well-defined drop in flow rate over the sampling period as the pressure in the canister rises closer to atmospheric pressure. Peak exposures during this period will give rise to a positive or negative bias in sampling results. This study was conducted to assess the influence of the time of occurrence of the peak on the performance of the method. Methods: Six flow controllers coupled with 400 mL evacuated canisters were tested in a small chamber (32 L) to evaluate sampling bias with respect to grab samples using canisters. All samples were pressurized with ultra-high purity nitrogen and analyzed with a 1 mL gas sample loop and a gas chromatograph/flame ionization detector. Toluene was used as a representative chemical of indoor/industrial contaminants. A 2 ppm concentration of toluene was generated in a chamber using a Dynamic Dilution System. Peaks of 200 ppm (100x) were generated at either the beginning of the sampling period to assess positive sampling bias or at the end of the sampling period to assess negative sampling bias. A photoionization detector was used to monitor the stability of the concentration of toluene throughout the sampling period. Two sampling periods were assessed: 4 hours and 8 hours representing 25% and 50% volume filled in the canister. Three experiments were run for each sampling period with six replicate canisters per experiment. The reference concentration was established using a series of canisters drawn directly from the chamber with no flow control device (grab sampler). Comparison of the reference values to the concentrations collected by the capillary flow controllers allowed for an assessment of the capillary flow controller bias. Results: The bias for all experiment trials ranged from 0.01% to -25% as compared to the reference concentrations. Relative standard deviations ranged from 1.0% to 16.3%. Reducing the volume filled in the canister from one-half to one-quarter decreased sampling bias from -25% to -16% for a peak at the end of the sampling period. Conclusions: Full-shift and half-shift sampling with small, evacuated canisters were found to provide results comparable to the reference values. Sampling bias can be reduced by filling the canister to a smaller percentage of the canister volume. [Description provided by NIOSH]
• Subjects:
  Occupational Health Safety Volatile Organic Compounds
• Keywords:
  Exposure Assessment Performance Capability Sampling Equipment Sampling Methods VOCs Volatile Organic Compounds
• Publisher:
  American Industrial Hygiene Association
• Document Type:
  Text
• Genre:
  Abstract or Summary
• Place as Subject:
  Maryland ; OSHA Region 3 ; West Virginia
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Division:
  RHD - Respiratory Health Division
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  94-95
• NIOSHTIC Number:
  nn:20066055
• Citation:
  AIHce 2016: American Industrial Hygiene Conference and Exposition Pathways to Progress, May 21-26, 2016, Baltimore, Maryland. Falls Church, VA: American Industrial Hygiene Association, 2016 May; :94-95
• Contact Point Address:
  R. LeBouf, CDC/NIOSH, Morgantown, WV
• CAS Registry Number:
  Toluene (CAS RN 108-88-3)
• Federal Fiscal Year:
  2016
• Peer Reviewed:
  False
• Source Full Name:
  AIHce 2016: American Industrial Hygiene Conference and Exposition Pathways to Progress, May 21-26, 2016, Baltimore, Maryland
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:90fd463299ab48527234b90dffd466ed14d75e46910cb7a8a30a7d9a91a176d1ac1d8b18491db9ea79f98f57862e33c2aab6462d16a86c1cb7787299b196d97b
• Download URL:
  https://stacks.cdc.gov/view/cdc/209134/cdc_209134_DS1.pdf
• File Type:
  [PDF - 1.44 MB ]