CIH - Certified Industrial Hygienist Air Sampling and Instrumentation Questions and Answers — Questions and Answers
Question 1: An industrial hygienist is sampling for respirable crystalline silica in a dusty construction environment using a 10-mm nylon cyclone. To ensure the cyclone correctly separates the respirable fraction according to the ACGIH/ISO/CEN convention, what is the required flow rate and corresponding 50% cut-point?
- 1.7 L/min for a 5.0 µm cut-point
- 2.5 L/min for a 4.0 µm cut-point (Correct answer)
- 2.0 L/min for a 10.0 µm cut-point
- 3.0 L/min for a 3.5 µm cut-point
Correct answer: 2.5 L/min for a 4.0 µm cut-point
To match the internationally accepted ACGIH/ISO/CEN respirable particulate matter curve, a 10-mm nylon cyclone (like the SKC Aluminum Cyclone) must be operated at a flow rate of 2.5 L/min. At this flow rate, it has a 50% cut-point (D50) of 4.0 µm, meaning it effectively captures 50% of particles with an aerodynamic diameter of 4.0 µm while collecting a progressively higher percentage of smaller particles and a lower percentage of larger particles.
Question 2: A key limitation of using Phase Contrast Microscopy (PCM) via NIOSH Method 7400 for analyzing asbestos samples is its inability to:
- Quantify fibers smaller than 5 µm in length.
- Be used for personal air sampling.
- Differentiate between asbestos and non-asbestos fibers. (Correct answer)
- Achieve a low enough detection limit for clearance sampling.
Correct answer: Differentiate between asbestos and non-asbestos fibers.
NIOSH Method 7400, which uses Phase Contrast Microscopy (PCM), is a method for counting fibers of a certain size but cannot distinguish between different types of fibers. Therefore, it counts all fibers (e.g., cellulose, gypsum, fiberglass) that meet the size criteria, not just asbestos. This can lead to an overestimation of the actual asbestos concentration. Transmission Electron Microscopy (TEM) is required to definitively identify fibers as asbestos.
Question 3: Which of the following direct-reading instruments is most suitable for detecting a broad range of volatile organic compounds (VOCs) at low parts-per-million (ppm) levels and operates by using a high-energy ultraviolet lamp to ionize the target molecules?
- Electrochemical Sensor
- Catalytic Combustion Sensor
- Non-Dispersive Infrared (NDIR) Analyzer
- Photoionization Detector (PID) (Correct answer)
Correct answer: Photoionization Detector (PID)
A Photoionization Detector (PID) uses a high-energy ultraviolet (UV) lamp to ionize airborne VOCs and other chemical compounds. The resulting charged ions create an electrical current that is proportional to the concentration of the contaminant. PIDs are known for their ability to detect a wide array of VOCs at low ppm or even parts-per-billion (ppb) levels, making them excellent for screening and real-time monitoring.
Question 4: An industrial hygienist is setting up a personal sampling pump for an 8-hour TWA sample. According to standard industrial hygiene practice, when must the pump's flow rate be checked with a calibrated flowmeter?
- Only at the beginning of the shift
- Only at the end of the shift
- At the beginning and end of the shift (Correct answer)
- Once per week, if used daily
Correct answer: At the beginning and end of the shift
To ensure the accuracy of the total volume of air sampled, it is standard and required practice to verify the flow rate of a personal sampling pump both before and after the sampling period. The pre- and post-sample flow rates are typically averaged to calculate the sample volume. This procedure accounts for any drift in the pump's flow rate that may have occurred during the sampling period due to factors like battery drain or filter loading.
Question 5: A significant advantage of using passive dosimeters for personal exposure monitoring compared to active sampling methods is that they:
- Provide real-time concentration readings.
- Do not require a sampling pump or calibration. (Correct answer)
- Are suitable for sampling all types of chemical hazards.
- Have higher sampling rates for short-duration tasks.
Correct answer: Do not require a sampling pump or calibration.
Passive dosimeters function based on the principle of diffusion, where airborne contaminants move from an area of higher concentration to a lower concentration across a membrane at a known rate. This process does not require a mechanical pump to draw air through the media. Consequently, they are simpler to use, less obtrusive to the worker, and eliminate the need for pump calibration.
Question 6: In the context of direct-reading gas monitors, the process of exposing the instrument to a known concentration of a target gas to adjust its response is correctly termed:
- Zeroing
- Bump Testing
- Calibration (or Span Calibration) (Correct answer)
- Field Screening
Correct answer: Calibration (or Span Calibration)
Calibration, often called span calibration, is the process of adjusting an instrument's reading to coincide with a known concentration (the span gas) of the target analyte. This ensures the instrument's response is accurate across its measurement range. Zeroing sets the instrument's baseline in clean air, and a bump test is a qualitative check to ensure sensors are responding, but only a span calibration provides quantitative accuracy.
CIH - Certified Industrial Hygienist Air Sampling and Instrumentation Questions and Answers
An industrial hygienist is sampling for respirable crystalline silica in a dusty construction environment using a 10-mm nylon cyclone.
To ensure the cyclone correctly separates the respirable fraction according to the ACGIH/ISO/CEN convention, what is the required flow rate and corresponding 50% cut-point?