CIH CIH - Certified Industrial Hygienist Sampling Strategy and Statistical Analysis Questions and Answers 2 — Questions and Answers
Question 1: What does a coefficient of variation (CV) represent in the context of analytical method performance?
- The recovery efficiency of the desorption solvent
- The relative standard deviation, expressing precision as a percentage of the mean (Correct answer)
- The detection limit of the analytical instrument
- The ratio of field blanks to total samples collected
Correct answer: The relative standard deviation, expressing precision as a percentage of the mean
The coefficient of variation (CV) is the relative standard deviation expressed as a percentage of the mean, used to quantify the precision (reproducibility) of an analytical method.
Question 2: According to OSHA's compliance sampling strategy, what constitutes an overexposure finding for an 8-hour TWA?
- Any single sample exceeding 50% of the PEL
- The measured TWA exceeds the PEL after accounting for sampling and analytical error (Correct answer)
- The geometric mean of all samples exceeds the action level
- Any instantaneous reading exceeding the ceiling value
Correct answer: The measured TWA exceeds the PEL after accounting for sampling and analytical error
OSHA considers an overexposure confirmed when the measured TWA exceeds the PEL even after subtracting the combined sampling and analytical error (CSAE) from the result.
Question 3: What is the purpose of a field blank in industrial hygiene air sampling?
- To calibrate the sampling pump flow rate
- To detect and correct for contamination introduced during sample handling and shipping (Correct answer)
- To measure background concentrations in the general plant environment
- To verify the integrity of the sampling media before use
Correct answer: To detect and correct for contamination introduced during sample handling and shipping
A field blank is an unexposed sample handled identically to field samples to detect contamination from transport, handling, or environmental sources that would falsely elevate results.
Question 4: When sampling for a substance with a ceiling limit (C), what is the correct sampling duration according to OSHA guidelines?
- Full 8-hour shift TWA sampling
- 15-minute short-term samples taken during peak exposure periods (Correct answer)
- 2-hour samples averaged over the work shift
- Instantaneous detector tube readings only
Correct answer: 15-minute short-term samples taken during peak exposure periods
Ceiling limits apply to 15-minute short-term exposures at times of expected peak concentrations; OSHA requires short-term sampling during maximum exposure conditions to evaluate compliance.
Question 5: What statistical tool is used to determine whether measured 95th percentile exposure significantly exceeds an OEL using lognormal exposure data?
- Student's t-test on raw sample values
- Land's exact method or lognormal upper confidence limit on the 95th percentile (Correct answer)
- Chi-square goodness-of-fit test
- ANOVA comparing means across worker groups
Correct answer: Land's exact method or lognormal upper confidence limit on the 95th percentile
Land's exact method calculates the upper confidence limit (UCL) on the 95th percentile of a lognormal distribution, which is the standard approach for evaluating whether upper-tail exposures exceed the OEL.
Question 6: In the context of industrial hygiene sampling, what is meant by 'combined sampling and analytical error' (CSAE)?
- The total variability introduced only by laboratory analysis
- The combined uncertainty from both field sampling and laboratory analysis expressed as a percentage (Correct answer)
- The difference between replicate samples collected simultaneously
- The error introduced by improper pump calibration alone
Correct answer: The combined uncertainty from both field sampling and laboratory analysis expressed as a percentage
CSAE combines the variability from both the sampling process (pump flow, media efficiency) and laboratory analysis (recovery, instrument precision) into one total uncertainty value at a specified confidence level.
CIH CIH - Certified Industrial Hygienist Sampling Strategy and Statistical Analysis Questions and Answers 2
What does a coefficient of variation (CV) represent in the context of analytical method performance?