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 marine chemist discovers that a tank previously certified 'Safe for Workers' now has an H₂S reading of 15 ppm. The correct immediate action is to:
Answer: Immediately void or suspend the certificate and require re-ventilation before re-testing
Any detected H₂S represents a change in conditions from the certified atmosphere; the certificate must be suspended and the space re-ventilated and re-tested before workers enter.
The 'Lower Flammable Limit' (LFL) and 'Lower Explosive Limit' (LEL) of a gas are:
Answer: The same concept expressed identically
LFL and LEL describe the same phenomenon — the minimum concentration of gas in air that will propagate flame — and the terms are used interchangeably in marine chemistry.
Under NFPA 306, which person is qualified to issue a marine chemist certificate?
Answer: A National Fire Protection Association (NFPA) licensed marine chemist
NFPA 306 requires that certificates be issued only by a marine chemist holding current NFPA certification, which requires passing a rigorous examination and demonstrating field competency.
When testing for toxic atmospheres in a freshly cleaned tank that held benzene cargo, which instrument is MOST appropriate for low-concentration detection?
Answer: Photoionization detector (PID)
PIDs can detect benzene at sub-ppm concentrations well below LEL and are the instrument of choice for assessing toxic hydrocarbon vapor levels where worker health limits apply.
A confined space atmosphere test shows 22% O₂, 8% LEL, and 5 ppm H₂S. Which certificate designation applies?
Answer: Neither Safe for Workers nor Safe for Hot Work
8% LEL exceeds the 5% LEL threshold for hot work, and the combined conditions of flammable vapor and H₂S make the space unsafe for unprotected workers; no standard certificate can be issued.
Electrochemical sensors used for oxygen detection can be compromised by long-term exposure to which compound commonly found in marine cargo tanks?
Answer: Chlorinated solvents and strong oxidizers
Chlorinated solvents and strong oxidizing agents can corrode electrochemical cell electrodes or interfere with the electrochemical reaction, leading to sensor degradation and inaccurate oxygen readings.
The purpose of a 'continuous atmosphere monitoring' requirement during hot work inside a marine confined space is to:
Answer: Detect any change in atmospheric conditions that would invalidate the safe-work certificate
Continuous monitoring during hot work provides real-time detection of atmospheric changes — such as vapor ingress or oxygen depletion — so work can be stopped before conditions become dangerous.