CMC Vessel-Specific Hazards 3 — Questions and Answers
Question 1: Which type of vessel cargo space requires testing for phosphine (PH3) as a primary concern during the marine chemist's inspection?
- Tank vessels carrying sulfuric acid
- Bulk carriers that have carried grain fumigated with aluminum phosphide (Correct answer)
- LNG carriers after boil-off operations
- Chemical tankers carrying methanol cargo
Correct answer: Bulk carriers that have carried grain fumigated with aluminum phosphide
Aluminum phosphide is commonly used to fumigate grain shipments and reacts with moisture to produce toxic phosphine gas, which can persist in cargo holds and surrounding spaces.
Question 2: On an inert gas-protected tanker, a marine chemist must enter the inert gas deck seal compartment. What is the primary atmospheric hazard?
- Oxygen enrichment from seal water aeration
- Oxygen deficiency from nitrogen or flue gas used as inertant
- Carbon monoxide from boiler exhaust inert gas
- Both B and C are correct (Correct answer)
Correct answer: Both B and C are correct
Inert gas system spaces can contain oxygen-deficient atmospheres from both the inert gas itself (CO2/N2/flue gas) and may also contain carbon monoxide when flue gas is the inertant source.
Question 3: A marine chemist finds a tank certified as 'Safe for Hot Work' but later determines the adjacent fuel oil double-bottom was not tested. Under NFPA 306, what must occur?
- The hot work can proceed since the primary tank is certified
- The certificate must be revoked and adjacent spaces must be tested and certified (Correct answer)
- Additional fire watches are sufficient to proceed
- The chief officer may sign a waiver to proceed
Correct answer: The certificate must be revoked and adjacent spaces must be tested and certified
NFPA 306 requires that all spaces adjacent to an area where hot work will be performed must be tested and included in the certification.
Question 4: What is the specific hazard associated with the void spaces between the cargo tanks and hull of a chemical tanker?
- Explosive gas from electrolytic action of cathodic protection
- Cargo vapor permeation creating toxic or flammable atmospheres (Correct answer)
- Spontaneous combustion of insulation materials
- Nitrogen blanketing from cargo handling operations
Correct answer: Cargo vapor permeation creating toxic or flammable atmospheres
Cargo vapors from chemical cargoes can permeate through tank walls into interbarrier or void spaces, creating hazardous atmospheres requiring testing before entry.
Question 5: During gas freeing of a crude oil tanker, when is it MOST dangerous for personnel to be on deck near tank openings?
- When the tank atmosphere reads below 10% LEL
- When the tank atmosphere passes through the flammable range (LEL to UEL) during purging (Correct answer)
- When the tank has been fully gas-freed to 0% LEL
- When oxygen is first introduced to the inerted tank
Correct answer: When the tank atmosphere passes through the flammable range (LEL to UEL) during purging
As the tank atmosphere passes through the explosive range during gas freeing, ignition of escaping vapors could occur from static discharge, sparks, or other ignition sources near the openings.
Question 6: A cargo tank on a product tanker previously carried tetraethyl lead (TEL) blended gasoline. What special precaution applies to the marine chemist's inspection beyond standard hydrocarbon testing?
- Testing for lead vapor using specialized photoionization detection
- Requiring supplied-air equipment regardless of hydrocarbon readings due to lead contamination (Correct answer)
- Double the normal ventilation time before entry
- Requiring the Lloyd's surveyor to be present during testing
Correct answer: Requiring supplied-air equipment regardless of hydrocarbon readings due to lead contamination
Tetraethyl lead is an extremely toxic organolead compound that can persist as residue in tanks; supplied-air breathing apparatus is required for any entry into tanks that have carried TEL-blended fuels.
Question 7: What condition defines an 'oxygen-enriched atmosphere' hazard in a vessel space according to OSHA standards?
- Oxygen concentration above 20.9%
- Oxygen concentration above 22% (Correct answer)
- Oxygen concentration above 21.5%
- Oxygen concentration above 23.5%
Correct answer: Oxygen concentration above 22%
OSHA defines an oxygen-enriched atmosphere as one containing more than 22% oxygen by volume, which significantly increases fire and explosion risk.
CMC Vessel-Specific Hazards 3
Which type of vessel cargo space requires testing for phosphine (PH3) as a primary concern during the marine chemist's inspection?