Analysis, Measurement, and Quality Assurance
Analysis, Measurement, and Quality Assurance tests whether you can produce defensible data: sampling strategy, instrument selection, calibration, chain of custody, statistics, and quality control. Items ask you to spot a sampling plan that cannot answer the exposure question or a result that should not be reported.
Core rules
- Sampling plan: define the decision, the agent, the averaging time (e.g., 8-hour TWA), the population, and the number of samples. Representative sampling beats convenient sampling.
- Methods: use validated methods (e.g., NIOSH or OSHA methods) with specified media, flow rate, and analytical technique; record everything.
- Quality control: calibration before and after use, field blanks, media blanks, duplicates, and chain-of-custody forms for legal or regulatory defensibility.
- Statistics: distinguish accuracy (closeness to truth) from precision (repeatability); report uncertainty and limit of detection; do not report below-LOD values as zero.
- Control charts: a point beyond three sigma signals a special cause; trends signal drift.
Worked example
A worker is sampled for solvent vapor: 4 hours at 100 ppm and 4 hours at 20 ppm. The 8-hour TWA is (100×4 + 20×4)/8 = 60 ppm. If the exposure limit is 50 ppm, the result exceeds it, even though the second half of the shift looked low. Reasoning: the TWA weights concentration by time; short high exposures can dominate. A single grab sample from the morning would have mischaracterized the shift.
Traps
- Using a grab sample to represent a full shift.
- Calibrating only before sampling, then discovering drift afterward.
- Reporting a result without the detection limit or uncertainty.
- Confusing precision with accuracy.
- Ignoring non-representative weather, production peaks, or worker tasks.