CMC Hazardous Materials Management & Containment 2 — Questions and Answers
Question 1: Under NFPA 306, what oxygen concentration range is considered 'safe' for normal entry into a marine vessel space?
- 16.0%–19.5%
- 19.5%–22.0% (Correct answer)
- 22.0%–23.5%
- 18.0%–21.0%
Correct answer: 19.5%–22.0%
NFPA 306 defines a safe oxygen atmosphere as 19.5% to 22.0% by volume for normal entry.
Question 2: Which document must a Certified Marine Chemist issue before hot work is permitted in or near a confined space on a vessel?
- Material Safety Data Sheet
- Certificate of Fitness (Correct answer)
- Hazard Communication Plan
- Confined Space Entry Permit
Correct answer: Certificate of Fitness
A Marine Chemist Certificate of Fitness (or Safe-for-Hot-Work certificate) is required before hot work begins on or near vessel spaces.
Question 3: A cargo tank that previously held benzene is classified as 'Not Safe for Workers' primarily because benzene's IDLH is:
- 500 ppm
- 250 ppm
- 50 ppm (Correct answer)
- 1000 ppm
Correct answer: 50 ppm
NIOSH sets benzene's IDLH at 500 ppm, but OSHA's permissible exposure limit (1 ppm) and carcinogenicity mean even low concentrations preclude worker safety.
Question 4: When a hazardous material spill occurs in a vessel's bilge, the FIRST action under MARPOL Annex I is to:
- Discharge overboard if distance from shore exceeds 12 nm
- Activate the oil-water separator and record in the Oil Record Book
- Notify port state control before taking any action
- Transfer the mixture to a slop tank and prevent overboard discharge (Correct answer)
Correct answer: Transfer the mixture to a slop tank and prevent overboard discharge
MARPOL Annex I requires preventing unauthorized overboard discharge; spilled oily mixtures must be contained and transferred to a slop tank pending proper disposal.
Question 5: The Lower Explosive Limit (LEL) of a flammable vapor represents the concentration at which:
- The vapor becomes immediately dangerous to life and health
- The air-vapor mixture is too lean to ignite (Correct answer)
- The vapor is too rich to sustain combustion
- The atmosphere is oxygen-enriched
Correct answer: The air-vapor mixture is too lean to ignite
The LEL is the minimum concentration of flammable vapor in air below which ignition cannot propagate because the mixture is too lean.
Question 6: Which containment method is most appropriate for a deck spill of a water-reactive hazardous liquid on a vessel?
- Dilute immediately with seawater from fire hoses
- Apply dry absorbent material and prevent water contact (Correct answer)
- Wash down with fresh water into the bilge
- Use foam blanket and drain to scuppers
Correct answer: Apply dry absorbent material and prevent water contact
Water-reactive materials can generate toxic or flammable gases when contacted with water; dry absorbents contain the spill without triggering the reaction.
Question 7: A marine chemist testing a tank finds 18% LEL for methane. This atmosphere is classified as:
- Safe for hot work
- Safe for workers but not hot work (Correct answer)
- Not safe for workers or hot work
- Inert and safe for entry
Correct answer: Safe for workers but not hot work
NFPA 306 generally permits worker entry when flammable gas reads below 10% LEL, but readings of 10–20% LEL typically require 'Safe for Workers but Not Hot Work' designation depending on site conditions.
CMC Hazardous Materials Management & Containment 2
Under NFPA 306, what oxygen concentration range is considered 'safe' for normal entry into a marine vessel space?