Atmospheric Hazard Testing Flashcards
7 cards from real CMC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Atmospheric Hazard Testing flashcards as text
Under NFPA 306, a 'Safe for Hot Work' certificate for a vessel tank is valid for a maximum of how long after issuance?
Answer: 24 hours
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.
When a photoionization detector (PID) is used to assess toxic vapor levels in a cargo tank, which factor most affects its accuracy?
Answer: The ionization potential (IP) of the target compound versus the lamp eV rating
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.
Carbon monoxide (CO) is particularly hazardous in marine spaces because it:
Answer: Is colorless and odorless, providing no sensory warning
CO is colorless and odorless, making it impossible to detect without instruments, and it binds to hemoglobin with ~240 times the affinity of oxygen.
Which gas is most likely to accumulate at the top of a poorly ventilated cargo hold rather than the bottom?
Answer: Hydrogen (H₂)
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.
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:
Answer: Test the atmosphere at the entry point before entering or inserting personnel
The atmosphere at the access point must be confirmed non-hazardous before any person or unprotected sampling equipment is deployed into the space.
The Threshold Limit Value–Ceiling (TLV-C) for a substance differs from TLV-TWA in that it:
Answer: Must never be exceeded even instantaneously
TLV-C is a concentration that must never be exceeded at any time during the workday, unlike the TWA which is averaged over 8 hours.
When calibrating a combustible gas indicator (CGI) for use in a tank that previously held gasoline, the technician should calibrate using:
Answer: Methane as the reference gas and apply a correction factor for gasoline
CGIs are typically calibrated with methane or pentane as reference gases, and published correction factors are applied when the target gas is a different hydrocarbon such as gasoline.