CMC Atmospheric Hazard Testing 3

Question 1

Under NFPA 306, a 'Safe for Hot Work' certificate for a vessel tank is valid for a maximum of how long after issuance?

Accepted Answer

24 hours

Answer

NFPA 306 specifies that a marine chemist's certificate is valid for no more than 24 hours, after which re-testing and re-certification are required.

Question 2

When a photoionization detector (PID) is used to assess toxic vapor levels in a cargo tank, which factor most affects its accuracy?

Accepted Answer

The ionization potential (IP) of the target compound versus the lamp eV rating

Answer

A PID lamp can only ionize compounds whose ionization potential is below the lamp's photon energy (eV); compounds with IP above the lamp rating give zero or false readings.

Question 3

Carbon monoxide (CO) is particularly hazardous in marine spaces because it:

Accepted Answer

Is colorless and odorless, providing no sensory warning

Answer

CO is colorless and odorless, making it impossible to detect without instruments, and it binds to hemoglobin with ~240 times the affinity of oxygen.

Question 4

Which gas is most likely to accumulate at the top of a poorly ventilated cargo hold rather than the bottom?

Accepted Answer

Hydrogen (H₂)

Answer

Hydrogen has a molecular weight of ~2 g/mol, far lighter than air (~29 g/mol), so it rises and accumulates at the highest points of an enclosed space.

Question 5

A marine chemist must re-test an inerted cargo tank before it can be certified for hot work. The FIRST step upon re-opening the tank is to:

Accepted Answer

Test the atmosphere at the entry point before entering or inserting personnel

Answer

The atmosphere at the access point must be confirmed non-hazardous before any person or unprotected sampling equipment is deployed into the space.

(CMC) Certified Marine Chemist Practice Test

(CMC) Certified Marine Chemist Practice Test

CMC Atmospheric Hazard Testing 3