CMC Flammable and Combustible Materials 5

Question 1

The primary reason for purging a cargo tank with inert gas BEFORE gas-freeing by ventilation is to:

Accepted Answer

Prevent the tank atmosphere from passing through the flammable range during the ventilation process

Answer

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.

Question 2

Under OSHA 29 CFR 1910.146, a confined space with a flammable atmosphere exceeding 10% LEL is classified as:

Accepted Answer

A hazardous atmosphere that requires permit-required confined space procedures

Answer

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.

Question 3

When a Marine Chemist tests a multi-level cargo hold or tank, atmospheric samples must be collected:

Accepted Answer

At multiple locations and levels including the top, middle, and bottom of the space

Answer

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.

Question 4

Electrostatic charge buildup during petroleum cargo transfer presents the greatest ignition risk when:

Accepted Answer

The tank atmosphere is within the flammable range between the LEL and UEL

Answer

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.

Question 5

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:

Accepted Answer

Request a new inspection and obtain a separate 'Safe for Hot Work' certificate before welding

Answer

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.

(CMC) Certified Marine Chemist Practice Test

(CMC) Certified Marine Chemist Practice Test

CMC Flammable and Combustible Materials 5