CIH Air Sampling and Instrumentation 5 — Questions and Answers
Question 1: A hygienist samples noise using a personal noise dosimeter. The dosimeter reading after an 8-hour shift is 87%. What is this worker's 8-hour TWA equivalent sound level?
- 87 dBA
- Less than 85 dBA (Correct answer)
- Approximately 89.4 dBA
- Exactly 90 dBA
Correct answer: Less than 85 dBA
A dose of 100% equals an 8-hour TWA of 90 dBA (OSHA criterion); 87% dose corresponds to a TWA slightly below 90 dBA, calculated as TWA = 16.61 × log10(D/100) + 90.
Question 2: Which type of air sampling pump is required when sampling in a potentially explosive atmosphere (e.g., solvent vapor above 10% LEL)?
- Standard AC-powered diaphragm pump
- Intrinsically safe (IS) certified personal sampling pump (Correct answer)
- Peristaltic pump with carbon-brush motor
- Any pump rated for outdoor use
Correct answer: Intrinsically safe (IS) certified personal sampling pump
Intrinsically safe pumps are designed to prevent ignition of flammable atmospheres by limiting electrical energy to levels that cannot cause ignition.
Question 3: The limit of detection (LOD) for an analytical method is defined as the analyte concentration producing a signal equal to:
- Two times the background noise
- Three times the standard deviation of the blank signal (Correct answer)
- Five percent of the calibration range
- The lowest calibration standard concentration
Correct answer: Three times the standard deviation of the blank signal
LOD is conventionally set at three times the standard deviation of blank measurements (3σ), representing the smallest detectable signal above noise.
Question 4: A hygienist wants to determine area airborne concentrations of a contaminant without disturbing workers. Which sampling approach is most appropriate?
- Personal sampler clipped to a stationary tripod in the breathing zone area
- Open-face filter cassette placed at a fixed location in the work area (Correct answer)
- Closed-face personal sampler worn by the supervisor
- Grab sample using a Tedlar bag collected manually
Correct answer: Open-face filter cassette placed at a fixed location in the work area
Open-face cassettes are used for area/general air monitoring to characterize the airborne environment without being placed in a worker's breathing zone.
Question 5: When preparing a sampling train for hydrogen sulfide using NIOSH Method 6013, the collection medium is:
- Activated charcoal tube
- Silica gel tube
- Cadmium sulfate-impregnated filter followed by a sulfuric acid impinger (Correct answer)
- Thermal desorption tube with Tenax sorbent
Correct answer: Cadmium sulfate-impregnated filter followed by a sulfuric acid impinger
NIOSH 6013 uses a cadmium sulfate-treated filter to collect H2S as cadmium sulfide for subsequent colorimetric or ion chromatographic analysis.
Question 6: A hygienist calibrates a sampling pump using a soap bubble meter. The bubble travels 500 mL in 15 seconds. What is the flow rate in L/min?
- 1.5 L/min
- 2.0 L/min (Correct answer)
- 0.5 L/min
- 3.0 L/min
Correct answer: 2.0 L/min
Flow rate = volume / time = 500 mL / 15 s = 33.3 mL/s × 60 s/min = 2,000 mL/min = 2.0 L/min.
Question 7: Which direct-reading instrument is best suited for detecting and quantifying low-level benzene in the presence of a complex hydrocarbon mixture?
- Non-dispersive infrared (NDIR) analyzer
- Photoionization detector (PID) with a 10.6 eV lamp (Correct answer)
- Flame ionization detector (FID) without separation
- Metal oxide semiconductor (MOS) sensor array
Correct answer: Photoionization detector (PID) with a 10.6 eV lamp
A PID with a 10.6 eV lamp ionizes benzene (IP = 9.24 eV) selectively and is widely used for low-ppm VOC detection in mixed environments.
CIH Air Sampling and Instrumentation 5
A hygienist samples noise using a personal noise dosimeter.
The dosimeter reading after an 8-hour shift is 87%.
What is this worker's 8-hour TWA equivalent sound level?