CMC Hot Work Procedures 2 — Questions and Answers
Question 1: A Marine Chemist is asked to certify a tank for hot work immediately after gas-freeing. What is the MOST critical pre-certification check?
- Verify combustible gas readings are below 10% LEL throughout the space (Correct answer)
- Confirm the tank has been washed with fresh water
- Check that adjacent tanks contain no cargo
- Ensure the tank coating has fully cured
Correct answer: Verify combustible gas readings are below 10% LEL throughout the space
Combustible gas concentration must be below 10% LEL throughout the space before a hot work certificate can be issued.
Question 2: During hot work on a tank bulkhead, the adjoining tank contains an inert atmosphere with residual hydrocarbon cargo. What is the correct action?
- Proceed if the work side reads below 10% LEL
- Prohibit hot work because the adjacent space poses a through-bulkhead ignition risk (Correct answer)
- Allow hot work if a fire watch monitors the adjacent tank
- Reduce the inert gas pressure before proceeding
Correct answer: Prohibit hot work because the adjacent space poses a through-bulkhead ignition risk
Hot work must not be performed on a bulkhead adjacent to a space containing flammable vapors or cargo, regardless of readings on the work side.
Question 3: Which condition would cause a Marine Chemist to DENY a hot work certificate in a freshly gas-freed tank?
- Oxygen reading of 20.9% by volume
- Combustible gas reading of 0% LEL at the entry point but 12% LEL in a low corner (Correct answer)
- Presence of ventilation equipment still running
- Temperature inside the tank is 95°F
Correct answer: Combustible gas reading of 0% LEL at the entry point but 12% LEL in a low corner
Any location within the space reading at or above 10% LEL disqualifies the entire space from hot work authorization.
Question 4: What is the purpose of a 'hot work permit' as distinct from a Marine Chemist certificate?
- It replaces the Marine Chemist certificate when a chemist is unavailable
- It is the vessel management authorization document that references the Marine Chemist findings (Correct answer)
- It certifies the welder is qualified to perform the work
- It documents the type of welding equipment approved for use
Correct answer: It is the vessel management authorization document that references the Marine Chemist findings
The hot work permit is issued by vessel management and incorporates the Marine Chemist's atmospheric findings as the basis for authorization.
Question 5: Slag from overhead welding falls into an open void space during authorized hot work. What is the IMMEDIATE required response?
- Continue work if the void space previously tested safe
- Stop hot work and inspect the void space for fire or smoldering material (Correct answer)
- Notify the Coast Guard before taking any action
- Increase ventilation flow to the void space
Correct answer: Stop hot work and inspect the void space for fire or smoldering material
Hot slag can ignite residues or coatings in void spaces; work must stop immediately and the affected space must be inspected.
Question 6: A Marine Chemist certificate for hot work is typically valid for how long before re-testing is required?
- 72 hours regardless of conditions
- Until conditions change or work is interrupted for more than a designated period, typically 4–8 hours (Correct answer)
- 24 hours, renewable by the vessel's chief officer
- Indefinitely as long as continuous ventilation is maintained
Correct answer: Until conditions change or work is interrupted for more than a designated period, typically 4–8 hours
NFPA 306 requires re-testing whenever conditions change or work is interrupted beyond defined periods; continuous monitoring and re-certification protocols apply.
Question 7: When performing hot work near a cofferdam that separates a cargo tank from a ballast tank, the Marine Chemist should test:
- Only the space where hot work will occur
- Only the cargo tank side
- Both the work space and all adjacent spaces including the cofferdam (Correct answer)
- The ballast tank only if it previously held petroleum cargo
Correct answer: Both the work space and all adjacent spaces including the cofferdam
All spaces adjacent to the hot work location, including cofferdams, must be tested to ensure no flammable vapor migration exists.
CMC Hot Work Procedures 2
A Marine Chemist is asked to certify a tank for hot work immediately after gas-freeing.
What is the MOST critical pre-certification check?