CIH Air Sampling and Instrumentation 4 — Questions and Answers
Question 1: A hygienist collects duplicate side-by-side personal samples. What is the primary purpose of collecting field duplicates?
- To double the total volume sampled for lower detection limits
- To assess the sampling and analytical error (precision) of the method (Correct answer)
- To provide a backup sample if one is lost in transit
- To compare morning versus afternoon exposure levels
Correct answer: To assess the sampling and analytical error (precision) of the method
Field duplicates quantify the combined sampling and analytical variability, allowing calculation of the overall method precision (CVT).
Question 2: Which ACGIH-defined aerosol fraction would a 4-mm-diameter particle with aerodynamic equivalent diameter (AED) of 4 µm be classified as?
- Inhalable fraction only
- Thoracic fraction only
- Respirable fraction (Correct answer)
- None of the above; it would be excluded
Correct answer: Respirable fraction
The respirable fraction includes particles with 50% cut point at 4 µm AED, so a 4 µm AED particle has a 50% probability of being captured in the respirable fraction.
Question 3: A hygienist needs to collect a wipe sample for beryllium surface contamination. Which wipe medium is specified by NIOSH Method 9100?
- Dry cotton gauze
- Ghost Wipe wetted with water (Correct answer)
- Dry polyester wipe
- Filter paper moistened with ethanol
Correct answer: Ghost Wipe wetted with water
NIOSH Method 9100 specifies Ghost Wipes pre-wetted with deionized water for beryllium surface wipe sampling.
Question 4: When using an impinger to collect an air sample for a water-soluble gas, the primary collection mechanism is:
- Inertial impaction onto a liquid surface
- Absorption of gas molecules into the liquid medium (Correct answer)
- Diffusion through a porous membrane into the liquid
- Electrostatic precipitation onto a charged liquid droplet
Correct answer: Absorption of gas molecules into the liquid medium
Impingers capture water-soluble gases primarily through gas absorption as the airstream bubbles through the collection liquid.
Question 5: A hygienist observes that a charcoal sorbent tube backup section contains more than 25% of the mass found in the front section. This indicates:
- The sample is acceptable with a correction factor applied
- Breakthrough has occurred, and the sample result is invalid (Correct answer)
- The analytical method requires two separate desorptions
- The sampling rate was too low
Correct answer: Breakthrough has occurred, and the sample result is invalid
When the backup section contains >25% of the front section's mass, breakthrough has occurred and the sample underestimates true exposure.
Question 6: A photoacoustic infrared (PAIR) monitor detects gases by measuring:
- Change in electrical conductivity of a heated sensor filament
- Sound waves generated when infrared-absorbing molecules are periodically excited (Correct answer)
- Fluorescence emission after UV excitation of target molecules
- Pressure change across a differential pressure transducer
Correct answer: Sound waves generated when infrared-absorbing molecules are periodically excited
PAIR instruments use a modulated IR source; absorbed energy causes periodic heating and expansion of gas molecules, generating acoustic waves detected by a microphone.
Question 7: For sampling asbestos fibers using phase contrast microscopy (PCM), the NIOSH 7400 method uses which filter type and pore size?
- PVC filter, 5.0 µm pore
- MCE filter, 0.8 µm pore (Correct answer)
- PTFE filter, 1.0 µm pore
- Polycarbonate filter, 0.4 µm pore
Correct answer: MCE filter, 0.8 µm pore
NIOSH 7400 specifies a 25-mm MCE filter with 0.8 µm pore size, which retains fibers while allowing the filter to be cleared for microscopic analysis.
CIH Air Sampling and Instrumentation 4
A hygienist collects duplicate side-by-side personal samples.
What is the primary purpose of collecting field duplicates?