CMC - Certified Marine Chemist Flammable and Combustible Materials Questions and Answers

Question 1

According to NFPA 30, a liquid with a closed-cup flash point at or above 100°F (37.8°C) is classified as what type of material?

Accepted Answer

Combustible Liquid

Answer

NFPA 30, 'Flammable and Combustible Liquids Code', defines a combustible liquid as one having a closed-cup flash point at or above 100°F (37.8°C). A flammable liquid is defined as having a flash point below 100°F (37.8°C).

Question 2

A Marine Chemist is testing a tank that previously contained hexane (vapor density ≈ 3.0). If any residual vapor is present, where should the chemist expect to find the highest concentration?

Accepted Answer

Concentrated in the lower portions and sumps of the tank.

Answer

Vapor density is the weight of a vapor compared to an equal volume of air (air = 1.0). A vapor density greater than 1.0 means the vapor is heavier than air and will sink, accumulating in the lowest points of a space, such as the tank bottom and sumps. Hexane's vapor density of approximately 3.0 makes it significantly heavier than air.

Question 3

A cargo tank containing residual flammable vapors is tested and found to be at 50% by volume (well above the UEL). A Marine Chemist advises the crew to begin ventilation to bring the tank to 0% LEL. What is the primary hazard during the initial phase of this ventilation process?

Accepted Answer

The atmosphere will pass through the explosive (flammable) range.

Answer

The atmosphere is initially above the Upper Explosive Limit (UEL), meaning there is too much fuel and not enough oxygen to support combustion. As ventilation introduces air, the concentration of flammable vapor will decrease, passing down through the explosive range (between the UEL and LEL) before reaching a safe level below the LEL. This period presents a significant explosion hazard if an ignition source is present.

Question 4

Hot work is planned for a bulkhead in a vessel's engine room. The adjacent space is a fuel oil tank that has been emptied but not cleaned. Which of the following is a valid method, per NFPA 306, for making the adjacent fuel tank safe for this hot work?

Accepted Answer

Cleaning the fuel tank until it is safe for hot work.

Answer

NFPA 306 requires that the space adjacent to the one where hot work is being performed must also be made safe. For a boundary bulkhead, this means the adjacent space must be cleaned to the point it is safe for hot work, inerted, or filled with water. Simply monitoring the work side or posting a watch is insufficient to control the hazard of heat transfer igniting the contents of the adjacent tank.

Question 5

A vessel's storeroom contains a large pile of rags soaked in linseed oil that were used for maintenance. What is the primary, unique fire hazard associated with these materials that a Marine Chemist or Competent Person should be concerned about?

Accepted Answer

Spontaneous combustion

Answer

Linseed oil and other drying oils cure through an exothermic oxidation process, meaning they generate heat. When rags soaked in these oils are piled together, the heat cannot dissipate. This can cause the temperature to rise to the oil's autoignition point, resulting in a fire without an external ignition source. This phenomenon is known as spontaneous combustion.

(CMC) Certified Marine Chemist Practice Test

(CMC) Certified Marine Chemist Practice Test

CMC - Certified Marine Chemist Flammable and Combustible Materials Questions and Answers