Flammable and Combustible Materials 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 Flammable and Combustible Materials flashcards as text
The primary reason for purging a cargo tank with inert gas BEFORE gas-freeing by ventilation is to:
Answer: Prevent the tank atmosphere from passing through the flammable range during the ventilation process
Purging with inert gas first reduces hydrocarbon concentration below the LEL so that when air is introduced during gas-freeing, the atmosphere never passes through the explosive range between LEL and UEL.
Under OSHA 29 CFR 1910.146, a confined space with a flammable atmosphere exceeding 10% LEL is classified as:
Answer: A hazardous atmosphere that requires permit-required confined space procedures
OSHA 1910.146 defines a hazardous atmosphere (triggering permit-required confined space requirements) as one with flammable vapor concentration exceeding 10% of its lower flammable limit.
When a Marine Chemist tests a multi-level cargo hold or tank, atmospheric samples must be collected:
Answer: At multiple locations and levels including the top, middle, and bottom of the space
Because vapor stratification can occur and different hazards may be present at different levels (heavy vapors pooling low, oxygen deficiency at various heights), NFPA 326 requires testing throughout the entire vertical extent of the space.
Electrostatic charge buildup during petroleum cargo transfer presents the greatest ignition risk when:
Answer: The tank atmosphere is within the flammable range between the LEL and UEL
Static electricity discharge is only capable of causing ignition if the surrounding atmosphere is in the flammable range; outside that range (too lean or too rich), a static spark will not ignite the atmosphere.
When a Marine Chemist has issued a 'Safe for Entry' certificate that explicitly excludes hot work, and a worker wishes to perform welding nearby, the correct action is:
Answer: Request a new inspection and obtain a separate 'Safe for Hot Work' certificate before welding
A Safe for Entry certificate and a Safe for Hot Work certificate are distinct — the more stringent hot work certification (requiring <10% LEL) must be separately obtained before any ignition-source work.
The term 'inerting' a cargo tank refers to:
Answer: Introducing an inert gas to reduce oxygen concentration below the level needed to support combustion
Inerting replaces or dilutes oxygen in the tank atmosphere with inert gas (typically flue gas or nitrogen) until oxygen drops below approximately 8% by volume, preventing ignition even if flammable vapors are present.
A Marine Chemist tests a space and finds: 0% LEL, 20.9% O₂, and 15 ppm H₂S. The correct certification decision is:
Answer: The space cannot be certified Safe for Entry without respiratory protection because H₂S at 15 ppm exceeds the OSHA ceiling limit
OSHA's H₂S ceiling limit is 20 ppm (ACGIH TLV-C is 1 ppm), and 15 ppm exceeds what would be considered acceptable for unprotected entry under many authorities; a Marine Chemist must account for all atmospheric hazards, not only LEL and oxygen.