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
A tank atmosphere reads 21% O₂ and 0% LEL, yet a worker reports dizziness upon entry. Which toxic gas is most likely responsible?
Answer: Carbon dioxide at elevated levels
CO₂ can accumulate to toxic concentrations while oxygen remains near normal; at 3–5% CO₂, symptoms of hypercapnia (dizziness, headache) occur even with adequate oxygen.
Under OSHA 29 CFR 1910.146, which condition by itself classifies a space as a 'permit-required confined space'?
Answer: The space has an internal atmosphere that could contain a serious safety or health hazard
A permit-required confined space is defined by OSHA as having limited entry/exit AND containing or potentially containing a serious safety/health hazard; it is the hazard potential that triggers permit requirements.
Infrared (IR) gas detectors used for hydrocarbon measurement in marine tanks have a significant limitation in that they:
Answer: Cannot detect hydrogen gas because H₂ has no IR absorption spectrum
Homonuclear diatomic molecules like H₂ are IR-inactive and produce no infrared absorption signal, making IR detectors blind to hydrogen.
A marine chemist performs atmosphere testing on a double-bottom tank after bulk liquid has been pumped out. The reading is 18% O₂, 0% LEL. The CORRECT certificate to issue is:
Answer: Neither — the atmosphere is oxygen-deficient and the space requires ventilation before entry
18% O₂ is below the OSHA/NFPA minimum of 19.5%, classifying the atmosphere as oxygen-deficient; no entry certificate can be issued until ventilation restores oxygen to the acceptable range.
When using a direct-reading sampling tube (colorimetric tube) to measure a specific gas, the marine chemist must account for:
Answer: Cross-sensitivity to other gases that may produce false color change
Colorimetric tubes can change color in response to interfering gases other than the target compound, potentially causing false positive or false negative readings.
The term 'inerting' of a cargo tank in marine operations refers to:
Answer: Reducing oxygen concentration below 8% using inert gas to prevent combustion
Inerting introduces inert gas (typically flue gas or nitrogen) to reduce oxygen below the limiting oxygen concentration (~8%), preventing ignition of flammable vapors.
Which phenomenon causes a combustible gas indicator to read artificially LOW in the presence of very high vapor concentrations (above 100% LEL)?
Answer: The 'over-range' or 'rich-burn' effect where excess fuel smothers the catalytic bead
At concentrations far above the stoichiometric point, insufficient oxygen causes incomplete combustion on the catalytic bead, producing a lower reading even as concentration increases — the 'rich mixture' failure mode.