CMC Chemical Sampling & Analysis Techniques 2

Question 1

When collecting an air sample from a confined space using a detector tube, what is the correct procedure for ensuring accurate results?

Accepted Answer

Draw the specified volume of air through the tube at the rate indicated by the manufacturer

Answer

Detector tubes must be used strictly per manufacturer specifications, including drawing the exact air volume at the correct rate, to ensure accurate readings.

Question 2

A Marine Chemist is sampling ballast water for oxygen content. Which instrument provides a real-time continuous measurement rather than a grab sample reading?

Accepted Answer

Electrochemical oxygen analyzer with in-line probe

Answer

Electrochemical analyzers with in-line probes continuously monitor oxygen levels, whereas titration and colorimetric kits analyze discrete grab samples.

Question 3

Which sampling method is most appropriate for determining the time-weighted average (TWA) concentration of benzene in a cargo hold over an 8-hour period?

Accepted Answer

Personal passive diffusion badge worn throughout the work shift

Answer

Passive diffusion badges integrate exposure over the entire wearing period, providing a true TWA concentration for comparison to occupational exposure limits.

Question 4

When using a flame ionization detector (FID) to measure hydrocarbon vapors in a tank, the instrument reads in units of ppm as what reference gas?

Accepted Answer

Methane or hexane equivalent, depending on calibration

Answer

FIDs measure total hydrocarbons referenced to a calibration gas, commonly methane (CH4) or hexane (C6H14), and results are expressed as ppm of that equivalent.

Question 5

A sample collected from the bottom of a cargo tank is found to have a different composition than one collected from the top. This stratification is most likely caused by:

Accepted Answer

Differences in vapor density causing heavier gases to sink and lighter gases to rise

Answer

Gases with higher molecular weights are denser and tend to accumulate at lower levels, while lighter gases rise, creating concentration gradients within a confined space.

(CMC) Certified Marine Chemist Practice Test

(CMC) Certified Marine Chemist Practice Test

CMC Chemical Sampling & Analysis Techniques 2