CIH Air Sampling and Instrumentation 3 — Questions and Answers
Question 1: An industrial hygienist needs to evaluate worker exposure to a mixture of organic solvents with synergistic health effects. Which sampling strategy is most appropriate?
- Sample only the highest-boiling-point component
- Use separate sorbent tubes optimized for each component and sum the fractions of their respective OELs (Correct answer)
- Sample with a single charcoal tube and report only the dominant compound
- Use a photoionization detector for instantaneous readings only
Correct answer: Use separate sorbent tubes optimized for each component and sum the fractions of their respective OELs
For synergistic mixtures, ACGIH and OSHA require that the sum of fractions (C1/TLV1 + C2/TLV2…) must not exceed 1.0, necessitating quantification of each component.
Question 2: The NIOSH Manual of Analytical Methods (NMAM) specifies that sorbent tubes must be stored at what temperature after field sampling?
- Room temperature (20–25°C)
- Refrigerator temperature (4°C or below) (Correct answer)
- Freezer temperature (−20°C)
- Ambient field temperature until shipment
Correct answer: Refrigerator temperature (4°C or below)
NMAM methods require refrigeration at ≤4°C after sampling to minimize analyte loss from desorption or degradation during transport.
Question 3: A rotameter used to calibrate a sampling pump reads differently when positioned horizontally versus vertically. What is the correct operating orientation?
- Horizontal, to eliminate gravity effects on the float
- Vertical with flow upward, as specified by the manufacturer (Correct answer)
- Any orientation, since rotameters are orientation-independent
- Inverted vertical, to maximize float travel
Correct answer: Vertical with flow upward, as specified by the manufacturer
Rotameters rely on gravity to position the float; they must be held vertically with flow upward for accurate readings.
Question 4: Which filter medium is recommended by NIOSH for collecting metal fume aerosols (e.g., lead fume) for ICP-MS analysis?
- Polyvinyl chloride (PVC) filter
- Mixed cellulose ester (MCE) filter (Correct answer)
- Polytetrafluoroethylene (PTFE) filter
- Glass fiber filter
Correct answer: Mixed cellulose ester (MCE) filter
MCE filters are recommended for metals because they dissolve readily in acid digestion, resulting in complete recovery for ICP-MS analysis.
Question 5: When using a direct-reading instrument for a confined space entry evaluation, which parameter should be checked FIRST before entering?
- Volatile organic compound level
- Oxygen concentration (Correct answer)
- Carbon monoxide level
- Hydrogen sulfide level
Correct answer: Oxygen concentration
Oxygen deficiency (below 19.5%) or enrichment (above 23.5%) is checked first because it affects combustibility readings and is immediately life-threatening.
Question 6: The relative standard deviation (RSD) for a NIOSH analytical method must be ≤ 0.05 to be acceptable. This value represents the:
- Absolute uncertainty in ppm units
- Coefficient of variation expressed as a decimal fraction (Correct answer)
- 95% confidence interval of the measurement
- Ratio of systematic to random error
Correct answer: Coefficient of variation expressed as a decimal fraction
RSD (coefficient of variation) = standard deviation / mean; a value ≤ 0.05 (5%) indicates acceptable analytical precision for NIOSH methods.
Question 7: An electrochemical sensor used for carbon monoxide monitoring must be checked with a known-concentration calibration gas at minimum how often during continuous use?
- Once per year
- Once per month
- Before each use or daily per manufacturer recommendation (Correct answer)
- Only when the alarm activates
Correct answer: Before each use or daily per manufacturer recommendation
NIOSH and most manufacturers require bump-testing or calibration verification before each use to ensure the sensor responds accurately.
CIH Air Sampling and Instrumentation 3
An industrial hygienist needs to evaluate worker exposure to a mixture of organic solvents with synergistic health effects.
Which sampling strategy is most appropriate?