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CIH practice questions

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Question 1Exposure Assessment

Which term describes the process of measuring or estimating the intensity, frequency, and duration of human exposure to an agent in the environment?

  1. Hazard identification
  2. Dose reconstruction
  3. Exposure assessment Correct answer.
  4. Risk characterization

Explanation

Exposure assessment quantifies contact between an agent and a receptor across time and includes magnitude, frequency, and duration. Risk characterization integrates exposure information with hazard information to describe risk.

Question 2Exposure Assessment

Where should a personal air sample be collected to estimate inhalation exposure?

  1. At the worker's waist, near the belt
  2. At the fixed location nearest the source
  3. At the exhaust duct of the room
  4. Within the worker's breathing zone Correct answer.

Explanation

Inhalation exposure is best represented by air in the worker's breathing zone, generally within about 6 to 9 inches of the nose and mouth. Air at the waist, at a fixed location, or in an exhaust duct may not represent what the worker actually inhales.

Question 3Exposure Assessment

A personal sample is collected at 2.0 L/min for 4.0 hours. What air volume, in liters, is collected?

  1. 480 L Correct answer.
  2. 2,400 L
  3. 8 L
  4. 120 L

Explanation

Volume is flow rate multiplied by time. Four hours equals 240 minutes, so 2.0 L/min times 240 min equals 480 L.

Question 4Exposure Assessment

What is the purpose of a field blank in an air sampling program?

  1. To detect contamination during handling and analysis Correct answer.
  2. To measure the workplace airborne concentration
  3. To identify the analyte's retention time
  4. To set the pump's flow rate before sampling

Explanation

A field blank is unexposed sampling media carried through the same handling, transport, storage, and analytical steps as the samples. Analyte found on the field blank indicates contamination introduced outside the workplace air sample.

Question 5Exposure Assessment

A similar exposure group (SEG) is best defined as a group of workers who:

  1. work in the same building and shift
  2. use the same type of respirator
  3. hold the same job title and pay grade
  4. have similar exposure profiles Correct answer.

Explanation

An SEG groups workers whose exposure profiles are expected to be similar for a given agent because of comparable tasks, controls, and conditions. Job title or location alone may be an inadequate basis for grouping.

Question 6Exposure Assessment

The limit of detection (LOD) of an analytical method is best described as the:

  1. concentration at which the method is most accurate
  2. lowest amount distinguishable from a blank Correct answer.
  3. highest concentration that can be measured without dilution
  4. average of the field blanks

Explanation

The LOD is the smallest amount that can be reliably distinguished from zero or a blank at a stated confidence level, often estimated as three times the standard deviation of blank responses. The upper measurement range and optimal accuracy range are separate method characteristics.

Question 7Exposure Assessment

Which device is considered a primary standard for calibrating an air sampling pump?

  1. Bubble flow meter Correct answer.
  2. Needle valve
  3. Calibrated orifice meter
  4. Variable-area rotameter

Explanation

A bubble flow meter measures gas volume and time directly, making it a primary flow standard. Rotameters and orifice meters are secondary standards that must themselves be calibrated.

Question 8Exposure Assessment

An OSHA permissible exposure limit expressed as an 8-hour time-weighted average refers to:

  1. the average concentration over an 8-hour work shift Correct answer.
  2. the maximum instantaneous concentration allowed
  3. a 15-minute average exposure limit
  4. the concentration that may never be exceeded for any duration

Explanation

An 8-hour time-weighted average averages exposure over a full 8-hour shift, allowing concentration fluctuations as long as the integrated average does not exceed the limit. Ceiling limits and short-term exposure limits address peak or brief exposures.

Question 9Exposure Assessment

A worker is exposed to 40 ppm for 2 hours, 10 ppm for 4 hours, and 0 ppm for 2 hours. What is the 8-hour TWA?

  1. 20 ppm
  2. 15 ppm Correct answer.
  3. 30 ppm
  4. 25 ppm

Explanation

The 8-hour TWA is the sum of each concentration multiplied by its duration, divided by 8 hours. The calculation is (40 times 2 plus 10 times 4 plus 0 times 2) divided by 8, which equals 15 ppm.

Question 10Exposure Assessment

An exposure limit for a mixture of two solvents with additive effects is evaluated by:

  1. multiplying the component concentrations
  2. averaging the component concentrations
  3. summing each component's ratio to its OEL Correct answer.
  4. using the lowest OEL among the components

Explanation

For additive effects, the mixture formula sums each component concentration divided by its own OEL. A sum greater than 1 indicates that the combined exposure exceeds the limit.

Question 11Exposure Assessment

What is the approximate concentration in mg/m³ of 100 ppm of a gas with molecular weight 60 at 25°C and 1 atm?

  1. 150 mg/m³
  2. 600 mg/m³
  3. 245 mg/m³ Correct answer.
  4. 24.5 mg/m³

Explanation

At 25°C and 1 atm, mg/m³ equals ppm multiplied by molecular weight and divided by 24.45. Thus 100 times 60 divided by 24.45 is approximately 245 mg/m³.

Question 12Exposure Assessment

When calibrating a personal sampling pump with a filter cassette, the calibration should be performed:

  1. with a representative sampling train in line Correct answer.
  2. with the cassette disconnected to avoid backpressure
  3. at a flow rate different from the sampling flow
  4. after the sample is collected only

Explanation

The sampler and media create backpressure that affects pump flow, so calibration must be done with a representative sampling train in line at the intended sampling flow rate. Calibrating without the sampler can produce an incorrect actual flow during sampling.

Question 13Exposure Assessment

In a sorbent tube sample, significant analyte found in the backup section indicates that:

  1. the analyte is a particulate
  2. breakthrough occurred and the result may underestimate exposure Correct answer.
  3. the pump flow rate was too low
  4. the sample is valid because the front section is saturated

Explanation

The backup section is intended to catch analyte that passes through the front section. Significant backup analyte means the sorbent capacity was exceeded, so the sample may underpredict the true exposure and is generally considered invalid or qualified.

Question 14Exposure Assessment

For a urinary metabolite with a short biological half-life, the most appropriate collection time to assess recent exposure is:

  1. at the end of the work shift Correct answer.
  2. at any time because timing does not matter
  3. 24 hours after exposure ends
  4. at the start of the next work shift

Explanation

A metabolite with a short half-life is cleared relatively quickly, so an end-of-shift sample best reflects same-day exposure. Sampling at the start of the next shift or 24 hours later may miss the exposure window.

Question 15Exposure Assessment

Increasing the number of personal samples within a similar exposure group generally:

  1. reduces the standard error of the mean Correct answer.
  2. increases the standard error of the mean
  3. eliminates all sampling and analytical error
  4. guarantees compliance with the OEL

Explanation

The standard error of the mean is the standard deviation divided by the square root of the number of samples. Increasing sample size reduces this uncertainty but does not remove measurement error or ensure compliance.

Question 16Exposure Assessment

Wipe sampling is most appropriate for assessing:

  1. airborne particulate concentration
  2. noise exposure
  3. surface contamination for dermal contact Correct answer.
  4. inhalation exposure to airborne gases and vapors

Explanation

Wipe samples collect removable residue from surfaces to estimate potential dermal contact or take-home contamination. They do not measure airborne concentrations or noise.

Question 17Exposure Assessment

Before use, a direct-reading gas detector should be calibrated using:

  1. distilled water
  2. a field blank cassette
  3. zero gas and a known span gas Correct answer.
  4. only untreated ambient room air

Explanation

Zero and span calibration establish the instrument baseline and response slope against known concentrations. Ambient room air may contain the analyte, and water or a blank cassette does not provide a known gas concentration.

Question 18Exposure Assessment

Which sampling medium is most appropriate for collecting an organic vapor such as toluene?

  1. Charcoal sorbent tube Correct answer.
  2. Polytetrafluoroethylene filter cassette
  3. Impinger with water
  4. Glass fiber filter

Explanation

Organic vapors are collected by adsorption onto sorbent media such as charcoal. Filters collect particulate matter, and water is not an effective collection medium for a nonpolar organic vapor.

Question 19Exposure Assessment

A cyclone sampler used for respirable particulate sampling typically has a 50% cut point of:

  1. 10 µm
  2. 4 µm Correct answer.
  3. 100 µm
  4. 0.1 µm

Explanation

The respirable particulate convention uses a 50% cut point of approximately 4 µm, while the inhalable convention uses 10 µm. Particles much smaller than 0.1 µm are in the ultrafine range.

Question 20Exposure Assessment

When sampling both particulate and vapor phases with a filter and sorbent tube in series, the filter should be placed:

  1. before the sorbent tube Correct answer.
  2. after the pump
  3. after the sorbent tube
  4. in parallel with the sorbent tube

Explanation

The filter is placed first so that particulate matter is removed before air reaches the sorbent. This prevents particles from contaminating or blocking the sorbent and allows the sorbent to collect the vapor phase.

Question 21Exposure Assessment

A probabilistic exposure assessment differs from a deterministic assessment primarily by:

  1. simulating outcomes from input distributions Correct answer.
  2. using only worst-case assumptions
  3. ignoring variability in exposure factors
  4. reporting a single point estimate

Explanation

Probabilistic methods assign distributions to input variables and simulate many possible outcomes to characterize variability and uncertainty. Deterministic methods typically use single point values, which may be conservative but do not describe the full range.

Question 22Exposure Assessment

The NIOSH accuracy criterion for sampling and analytical methods states that the method should be accurate within:

  1. ±5% at the 50% confidence level
  2. ±10% at the 90% confidence level
  3. ±25% at the 95% confidence level Correct answer.
  4. ±50% at the 99% confidence level

Explanation

The NIOSH accuracy criterion requires overall sampling and analytical accuracy of plus or minus 25% at the 95% confidence level over the evaluated range. The other combinations misstate either the tolerance or the confidence level.

Question 23Exposure Assessment

A sampling result is below the OEL, but the upper confidence limit of the mean exceeds it. The most appropriate interpretation is:

  1. the exposure is definitively compliant with the OEL
  2. the sample should be discarded
  3. additional sampling is needed to resolve uncertainty Correct answer.
  4. the OEL should be divided by the result

Explanation

Statistical uncertainty means the true mean exposure could exceed the OEL even though the point estimate is below it. Additional sampling or a refined strategy is needed before concluding compliance.

Question 24Exposure Assessment

Two SEGs have the same mean exposure, but SEG A has much greater between-worker variability. To characterize the 95th percentile exposure:

  1. more samples are generally needed for SEG A Correct answer.
  2. only area samples are needed
  3. fewer samples are needed for SEG A
  4. the same number of samples is sufficient for both

Explanation

Greater between-worker variability widens the distribution and increases the sample size needed to estimate an upper percentile with the same confidence. Equal sample numbers would provide less precision for the more variable group.

Question 25Exposure Assessment

Non-differential exposure misclassification in an epidemiological exposure assessment tends to:

  1. bias effect estimates toward the null Correct answer.
  2. increase the true variance of exposure
  3. eliminate confounding
  4. always exaggerate the exposure-response relationship

Explanation

When exposure is misclassified randomly and independently of the health outcome, observed associations are generally attenuated toward the null. This differs from differential misclassification, which can bias in either direction.

Question 26Exposure Assessment

In industrial hygiene, a worker's exposure to an airborne contaminant is best defined as which of the following?

  1. Contact of an agent with the outer boundary of a person over a period of time Correct answer.
  2. The total mass of an agent that is deposited in the lung during a work shift
  3. The amount of an agent that is absorbed into the bloodstream after inhalation
  4. The concentration of an agent measured at a fixed point in the workplace

Explanation

Exposure is contact between an agent and the outer boundary of the body (skin, respiratory tract, eyes) over time; it is the potential for dose, not the dose itself. Dose refers to the amount that actually crosses the boundary and is absorbed or deposited.

Question 27Exposure Assessment

A short-term exposure limit (STEL) is best described as which of the following?

  1. A peak value that may be exceeded up to four times during a workday
  2. A 15-minute TWA that should not be exceeded at any point in the workday Correct answer.
  3. An 8-hour time-weighted average that may be exceeded on any single shift
  4. A concentration that may be exceeded for up to 60 minutes per shift

Explanation

A STEL is a 15-minute time-weighted average that should not be exceeded at any time during the workday, even when the 8-hour TWA is within its limit. It supplements the 8-hour limit to control short, intense exposures.

Question 28Exposure Assessment

A ceiling limit for an airborne contaminant is best described as which of the following?

  1. A concentration that applies only to workers on shifts longer than 10 hours
  2. A concentration that must not be exceeded at any time during the exposure Correct answer.
  3. An average concentration that may be exceeded on any single workday
  4. A 15-minute time-weighted average that may be exceeded four times per shift

Explanation

A ceiling is an instantaneous maximum that must never be exceeded, and it is applied to agents whose toxicity is driven by brief high concentrations rather than by the shift-long average. It is monitored with direct-reading instruments or short grab samples.

Question 29Exposure Assessment

A gas concentration of 0.5% by volume corresponds to which concentration in parts per million?

  1. 50 ppm
  2. 50,000 ppm
  3. 500 ppm
  4. 5,000 ppm Correct answer.

Explanation

One percent by volume equals 10,000 ppm, so volume percent is converted to ppm by multiplying by 10,000. Multiplying 0.5 by 10,000 gives 5,000 ppm.

Question 30Exposure Assessment

A similar exposure group (SEG) is best described as which of the following?

  1. All workers with the same job title in a company
  2. All workers who report to the same supervisor and work the same shift schedule
  3. A group of workers with similar tasks, materials, and controls Correct answer.
  4. All workers employed in the same department of a single facility

Explanation

An SEG is defined by expected similarity of exposure, which arises from comparable tasks, materials, processes, and controls. Organizational boundaries such as department or supervisor do not by themselves establish exposure similarity.

Question 31Exposure Assessment

A grab sample used in exposure assessment is best described as which of the following?

  1. A sample collected over a period of seconds to a few minutes Correct answer.
  2. A sample collected continuously and averaged over 15 minutes
  3. A sample collected on a sorbent tube at a low flow rate for a full shift
  4. A sample collected continuously over an entire 8-hour work shift

Explanation

Grab samples are short-duration collections used to characterize peak or task-specific concentrations at a point in time. They are not representative of the full shift unless repeated, but they are valuable for ceiling and short-term comparisons.

Question 32Exposure Assessment

In a colorimetric detector tube, the airborne concentration is determined primarily from which observation?

  1. The length of the color change after a fixed number of pump strokes Correct answer.
  2. The mass of reagent consumed, measured by weighing the tube
  3. The intensity of the color change compared with a printed reference chart
  4. The time required for the reagent to change color completely

Explanation

Detector tubes rely on a length-of-stain reaction in which a known volume of air (set by the number of pump strokes) produces a colored zone whose length is proportional to the amount of contaminant. The tube is read against graduations printed on it.

Question 33Exposure Assessment

For a personal air sample, the breathing zone is best described as which of the following?

  1. Within 6 inches (15 cm) of the chest and shoulders
  2. The collar or lapel area of the worker's shirt, on the side facing the work
  3. A 9-inch (23 cm) radius hemisphere centered on the nose and mouth Correct answer.
  4. Within 3 feet (1 m) of the worker in any direction

Explanation

The breathing zone is defined as a hemisphere extending about 9 inches (23 cm) from the nose and mouth, and the sampler inlet is placed there so that the sample represents what the worker actually inhales.

Question 34Exposure Assessment

A personal filter sample collected 480 L of air and the filter was found to contain 0.72 mg of particulate. What is the airborne concentration?

  1. 1.5 mg/m³ Correct answer.
  2. 15 mg/m³
  3. 0.15 mg/m³
  4. 0.67 mg/m³

Explanation

Concentration equals mass divided by air volume expressed in cubic meters. Since 480 L equals 0.48 m³, dividing 0.72 mg by 0.48 m³ gives 1.5 mg/m³.

Question 35Exposure Assessment

How does the IOM inhalable sampler differ from a closed-face 37-mm cassette?

  1. It collects only the respirable fraction and is operated at 1.7 L/min
  2. It is used only for vapor-phase contaminants rather than aerosols
  3. The filter is housed inside the sampler body so all collected material is analyzed Correct answer.
  4. It uses a cyclone to remove particles larger than 4 micrometers

Explanation

In the IOM sampler the filter sits within the sampler body, so particles that would otherwise deposit on cassette walls are retained and analyzed, giving a truer inhalable-fraction sample. It is operated at 2 L/min and does not use a size-selective inlet.

Question 36Exposure Assessment

Silica gel is generally preferred over coconut-shell charcoal for sampling which of the following?

  1. Nonpolar solvents such as toluene and xylene
  2. Saturated aliphatic hydrocarbons such as hexane
  3. Polar compounds such as methanol and amines Correct answer.
  4. Halogenated solvents such as trichloroethylene

Explanation

Charcoal is a nonspecific adsorbent that works well for nonpolar and moderately polar organic vapors, whereas silica gel is used for very polar, low-molecular-weight compounds that are poorly retained on charcoal. Matching sorbent polarity to analyte polarity drives method selection.

Question 37Exposure Assessment

What is the primary purpose of submitting a field blank with a batch of personal samples?

  1. Establish the desorption efficiency of the sorbent used in the samples
  2. Assess contamination picked up during handling, transport, and storage Correct answer.
  3. Verify that the pump held its calibrated flow rate throughout the shift
  4. Determine the method's limit of detection for each batch of samples

Explanation

A field blank is carried to the field, left unopened, and analyzed with the samples, so any analyte found on it reflects contamination introduced during handling, transport, and storage. Sample results are corrected by subtracting the blank value.

Question 38Exposure Assessment

A sorbent tube method specifies a maximum recommended sample volume of 10 L. At a pump flow rate of 0.05 L/min, what is the longest acceptable sampling time?

  1. 200 minutes Correct answer.
  2. 100 minutes
  3. 500 minutes
  4. 20 minutes

Explanation

Sample volume equals flow rate multiplied by sampling time, so time equals volume divided by flow. Dividing 10 L by 0.05 L/min gives 200 minutes, beyond which breakthrough of the sorbent bed becomes likely.

Question 39Exposure Assessment

A photoionization detector fitted with a 10.6 eV lamp responds poorly to which of the following compounds?

  1. Toluene
  2. Benzene
  3. Methane Correct answer.
  4. Trichloroethylene

Explanation

A PID can only ionize molecules whose ionization potential is below the lamp energy. Methane's ionization potential of about 12.7 eV exceeds 10.6 eV, so it is essentially invisible to this lamp and requires a higher-energy lamp or a flame ionization detector.

Question 40Exposure Assessment

The 10-mm nylon cyclone used for personal respirable dust sampling must be operated at which flow rate to match the respirable sampling convention?

  1. 1.7 L/min Correct answer.
  2. 2.5 L/min
  3. 0.5 L/min
  4. 1.0 L/min

Explanation

The 10-mm nylon cyclone is calibrated to provide the respirable convention when operated at 1.7 L/min. Running it at a different flow shifts the cut point and invalidates the size-selective result.

Question 41Exposure Assessment

A worker is exposed to 20 ppm of a solvent for a 12-hour shift with no other exposure. What is the exposure expressed as an 8-hour time-weighted average?

  1. 20 ppm
  2. 24 ppm
  3. 30 ppm Correct answer.
  4. 13.3 ppm

Explanation

The 8-hour TWA is the total exposure dose divided by 8 hours regardless of actual shift length. Multiplying 20 ppm by 12 hours and dividing by 8 hours gives 30 ppm.

Question 42Exposure Assessment

The Brief and Scale model for unusual work schedules adjusts an occupational exposure limit by doing which of the following?

  1. Raising the limit in proportion to the length of the longer shift
  2. Converting the limit to a 24-hour average exposure value
  3. Leaving the limit unchanged but requiring more frequent sampling
  4. Lowering the limit to account for shorter recovery between shifts Correct answer.

Explanation

The model recognizes that a longer shift leaves fewer off-duty hours for recovery and elimination of the agent, so the permissible average concentration is reduced. The adjustment is based on the ratio of exposure hours to recovery hours.

Question 43Exposure Assessment

Which practice is essential when preparing sorbent tubes for shipment to the laboratory after sampling?

  1. Leave the tube open so residual vapor can escape before it is capped and shipped
  2. Cap both ends, label the tube, and ship with field blanks and chain-of-custody Correct answer.
  3. Heat the tube to 100 degrees C to drive off moisture before it is shipped
  4. Remove the sorbent sections and place them together in one vial for shipping

Explanation

Tubes must be capped at both ends immediately after sampling, labeled, and shipped with the appropriate blanks and documentation so that sample integrity and identity are preserved. Breaking the tube or heating it destroys the sample.

Question 44Exposure Assessment

Which sampling approach best characterizes a brief, task-based peak exposure to a solvent that causes acute central nervous system effects?

  1. A urine sample collected at the end of the work shift
  2. A charcoal tube operated at 0.05 L/min for the entire shift
  3. A data-logging direct-reading instrument worn during the task Correct answer.
  4. A 37-mm cassette operated at 2 L/min for the entire shift

Explanation

Peak exposures lasting minutes require an instrument with a short response time and time-resolved data logging; a full-shift integrated sample averages the peak away. Biological monitoring reflects absorbed dose and cannot resolve the timing of the peak.

Question 45Exposure Assessment

The vapor hazard ratio for a volatile liquid is used to accomplish which of the following?

  1. Determine the desorption efficiency of a sorbent tube Correct answer.
  2. Set the flow rate for a personal sampling pump
  3. Establish the odor threshold of a solvent in the workplace
  4. Rank the relative inhalation hazard of volatile liquids

Explanation

The vapor hazard ratio compares the saturated vapor concentration of a liquid with its occupational exposure limit, so a high ratio signals that realistic airborne concentrations can greatly exceed the limit. It is a screening tool for ranking inhalation hazards of volatile liquids.

Question 46Exposure Assessment

A worker wears a sampler for 6 hours of an 8-hour shift at a measured average of 60 ppm and is unexposed for the remaining 2 hours. If the 8-hour limit is 50 ppm, what is the 8-hour TWA and how does it compare with the limit?

  1. 48 ppm, which is below the limit
  2. 45 ppm, which is below the limit Correct answer.
  3. 30 ppm, which is below the limit
  4. 60 ppm, which is above the limit

Explanation

The 8-hour TWA is the total dose (60 ppm times 6 hours) divided by 8 hours, giving 45 ppm. Because the unsampled period is known to be unexposed, it legitimately dilutes the average and the result is below the limit.

Question 47Exposure Assessment

Personal exposures in a similar exposure group are lognormally distributed with a geometric mean of 2 ppm and a geometric standard deviation of 2.5. What is the estimated 95th percentile exposure?

  1. 5 ppm
  2. About 12.5 ppm
  3. About 20 ppm
  4. About 9 ppm Correct answer.

Explanation

For a lognormal distribution the 95th percentile equals the geometric mean multiplied by the geometric standard deviation raised to the 1.645 power. Here 2 ppm times 2.5^1.645 equals approximately 9 ppm.

Question 48Exposure Assessment

A preliminary study of a similar exposure group gives a standard deviation of 1.0 ppm. How many samples are needed to estimate the group mean with a 95% confidence interval half-width of 0.5 ppm?

  1. 8 samples
  2. 16 samples Correct answer.
  3. 12 samples
  4. 4 samples

Explanation

The required sample size is (z times the standard deviation divided by the desired half-width) squared. Using z of 1.96 gives (1.96 times 1.0 divided by 0.5) squared, about 15.4, which rounds up to 16 samples.

Question 49Exposure Assessment

Exposures in a group are lognormally distributed with a geometric mean of 5 ppm and a geometric standard deviation of 3. Approximately what percentage of exposures exceeds 50 ppm?

  1. About 2% Correct answer.
  2. About 0.5%
  3. About 16%
  4. About 10%

Explanation

The standardized normal deviate is the natural logarithm of 50 divided by 5, all divided by the natural logarithm of 3, giving about 2.10. The upper-tail area beyond z of 2.10 is roughly 1.8%, or about 2%.

Question 50Exposure Assessment

Why must dermal exposure be evaluated for a substance carrying a skin notation even when measured air concentrations are below the occupational exposure limit?

  1. Skin notation means the substance is a sensitizer that produces contact dermatitis
  2. Dermal absorption can add substantially to total dose even when air levels are low Correct answer.
  3. Skin notation indicates the airborne OEL already includes an allowance for dermal uptake
  4. Skin notation applies only to pesticides and other agricultural chemicals

Explanation

A skin notation signals that the agent can be absorbed through intact skin in amounts that may contribute significantly to total body burden. Airborne limits alone therefore do not control the hazard, and skin contact must be assessed and controlled separately.