CMC Chemical Sampling & Analysis Techniques 3

Question 1

A Marine Chemist must verify that a tank atmosphere is below 10% LEL before hot work. The CGI reads 8% LEL. What is the correct action?

Accepted Answer

Do not issue the certificate; the space must be further ventilated until readings are consistently below 10% LEL at all sampling points

Answer

A single reading of 8% LEL is at the threshold and may not be representative of all areas; consistent readings below 10% LEL at all required points must be confirmed before issuing a hot work certificate.

Question 2

Which analytical technique is most commonly used in a laboratory to confirm the identity and quantify trace concentrations of chlorinated solvents in a tank atmosphere sample collected on a sorbent tube?

Accepted Answer

Gas chromatography with electron capture detection (GC-ECD)

Answer

GC-ECD provides excellent sensitivity and selectivity for halogenated compounds, making it the standard method for confirming chlorinated solvent identities and concentrations.

Question 3

During hydrogen sulfide (H2S) sampling in a sludge tank, the detector reads 0 ppm at the hatch but a longer sampling probe at 6 feet depth reads 200 ppm. What does this demonstrate?

Accepted Answer

H2S can stratify near tank surfaces and sediments; sampling at multiple depths is essential

Answer

H2S, being heavier than air, can accumulate at lower levels near sludge layers while near-hatch readings appear safe, demonstrating the necessity of multi-depth sampling.

Question 4

What is the purpose of a zero-air calibration check performed on a photoionization detector (PID) before atmospheric sampling?

Accepted Answer

To confirm the instrument reads zero in clean, hydrocarbon-free air and establish a baseline

Answer

A zero-air check ensures the PID is not drifting or contaminated from previous use, establishing a clean baseline before measurements in the field.

Question 5

When a Marine Chemist collects an air sample using activated charcoal sorbent tubes, the sample must be sealed and shipped to the laboratory under what condition?

Accepted Answer

Capped, labeled with sampling data, stored cold (4°C), and shipped promptly with chain-of-custody documentation

Answer

Activated charcoal tubes must be capped immediately after sampling, refrigerated, and accompanied by chain-of-custody records to prevent desorption losses and ensure sample integrity.

(CMC) Certified Marine Chemist Practice Test

(CMC) Certified Marine Chemist Practice Test

CMC Chemical Sampling & Analysis Techniques 3