CMC - Certified Marine Chemist Flammable and Combustible Materials Questions and Answers 1 — 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?
- Flammable Liquid
- Combustible Liquid (Correct answer)
- Volatile Liquid
- Inert Liquid
Correct answer: Combustible Liquid
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?
- Evenly distributed throughout the tank.
- Stratified in a layer near the top of the tank.
- Concentrated in the lower portions and sumps of the tank. (Correct answer)
- Adhering only to the vertical surfaces of the tank.
Correct answer: Concentrated in the lower portions and sumps of the tank.
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?
- The oxygen level will drop to a dangerously low concentration.
- The atmosphere will pass through the explosive (flammable) range. (Correct answer)
- The ventilation will cause a static electricity discharge.
- The concentration of toxic components will increase tenfold.
Correct answer: The atmosphere will pass through the explosive (flammable) range.
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?
- Securing a fire watch on the opposite side of the bulkhead.
- Pressurizing the fuel tank with compressed air to prevent vapor leakage.
- Testing the engine room side only for flammable vapors.
- Cleaning the fuel tank until it is safe for hot work. (Correct answer)
Correct answer: Cleaning the fuel tank until it is safe for hot work.
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?
- Spontaneous combustion (Correct answer)
- Corrosive reaction with steel
- Rapid oxygen displacement
- High vapor pressure
Correct answer: Spontaneous combustion
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.
Question 6: A Marine Chemist is testing a tank that has been inerted with nitrogen. The oxygen meter reads 5%, and the chemist attempts to use a standard catalytic combustion-type Combustible Gas Indicator (CGI) to check for flammable vapors. The CGI reads 0% LEL. Why is this LEL reading unreliable?
- The nitrogen gas chemically neutralizes the flammable vapors.
- The CGI is not calibrated for use in atmospheres containing nitrogen.
- Catalytic combustion sensors require a minimum oxygen concentration to function correctly. (Correct answer)
- The low temperature of the nitrogen gas prevents the sensor from working.
Correct answer: Catalytic combustion sensors require a minimum oxygen concentration to function correctly.
A standard catalytic combustion (or hot-bead) LEL sensor works by burning a sample of the atmosphere on a heated filament. This combustion process requires oxygen. Most manufacturers specify a minimum oxygen level, typically between 10% and 12%, for the sensor to provide an accurate reading. In an oxygen-deficient atmosphere (5% O2), the sensor will give a false low or zero reading.
CMC - Certified Marine Chemist Flammable and Combustible Materials Questions and Answers 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?