CMC Cargo Tank Cleaning Procedures & Residue Management 2 — Questions and Answers
Question 1: When determining a tank cleaning procedure for a chemical tanker, which document serves as the primary operational reference for cargo-specific cleaning requirements and compatibility?
- The vessel's ISM Safety Management System manual
- MARPOL Convention Annex II alone
- The Chemical Data Guide or the tanker company's proprietary tank cleaning guide (Correct answer)
- OSHA 29 CFR 1910.146 confined space standard
Correct answer: The Chemical Data Guide or the tanker company's proprietary tank cleaning guide
The Chemical Data Guide (e.g., Witherby's) or a tanker company's tank cleaning guide provides cargo-by-cargo cleaning sequences, compatibility matrices, and wall wash criteria.
Question 2: Why is a cargo's miscibility with water an important consideration in planning tank cleaning operations?
- It determines the required pump capacity for final cargo discharge
- It determines whether water washing is effective or if alternative solvents are needed first (Correct answer)
- It determines the cargo's flash point and fire hazard classification
- It determines the required ventilation rate during gas-freeing
Correct answer: It determines whether water washing is effective or if alternative solvents are needed first
Water-miscible cargoes dissolve in wash water and are effectively removed by water washing, while water-immiscible cargoes require a compatible solvent pre-flush before water washing can be effective.
Question 3: During hot-water tank washing operations, what is the primary atmospheric hazard that increases compared to cold-water washing?
- Increased corrosion rate of tank coatings, releasing toxic decomposition products
- Enhanced volatilization of cargo residues, potentially intensifying flammable or toxic vapor generation (Correct answer)
- Excessive water pressure causing structural fatigue and metal particle release
- Crystallization of dissolved salts creating a conductive dust hazard
Correct answer: Enhanced volatilization of cargo residues, potentially intensifying flammable or toxic vapor generation
Elevated water temperature increases the vapor pressure of cargo residues, generating more vapors and potentially creating or worsening a flammable or toxic atmosphere during washing.
Question 4: What is 'wall wash testing' used for in chemical tanker operations?
- Testing the structural integrity and thickness of tank walls under hydrostatic pressure
- Verifying that a tank has been adequately cleaned so the next cargo will not be contaminated (Correct answer)
- Measuring the remaining thickness of anti-corrosion tank coating
- Checking for crevice corrosion on tank internals before loading a corrosive cargo
Correct answer: Verifying that a tank has been adequately cleaned so the next cargo will not be contaminated
Wall wash testing involves wiping a solvent across cleaned tank surfaces and analyzing the solution to confirm residue levels are below limits that would contaminate the next cargo.
Question 5: Which agency enforces MARPOL Annex II cargo tank cleaning and discharge requirements for chemical tankers operating in United States waters?
- The Environmental Protection Agency (EPA) under RCRA authority
- The Occupational Safety and Health Administration (OSHA)
- The United States Coast Guard (USCG) (Correct answer)
- The National Transportation Safety Board (NTSB)
Correct answer: The United States Coast Guard (USCG)
The USCG is the primary federal agency responsible for enforcing MARPOL requirements, including Annex II cargo tank cleaning and washings discharge rules, in US waters.
Question 6: What is the Marine Chemist's specific role with respect to cargo tank residue conditions before personnel may enter for cleaning?
- To determine the residue volume and update the cargo manifest accordingly
- To test the tank atmosphere and issue certification that conditions are safe for personnel entry (Correct answer)
- To calculate the financial liability for cargo loss attributable to residue
- To approve the tank cleaning program and select the washing agent
Correct answer: To test the tank atmosphere and issue certification that conditions are safe for personnel entry
A Marine Chemist evaluates the tank atmosphere for oxygen content, flammability, and toxicity, then certifies whether conditions meet safety requirements for personnel entry under NFPA 306.
Question 7: When a tank survey reveals that residue from a previous cargo is chemically reactive with the intended next cargo, what is the required course of action?
- Load the new cargo immediately to dilute and neutralize the reactive residue
- Perform additional cleaning until the tank is certified free of reactive residue (Correct answer)
- Permanently condemn the tank and notify the classification society
- Apply a chemical inhibitor to the residue and seal the tank for later treatment
Correct answer: Perform additional cleaning until the tank is certified free of reactive residue
Reactive cargo residues pose serious chemical reaction, fire, and explosion hazards; additional cleaning must be performed until the tank is certified safe for the next cargo.
CMC Cargo Tank Cleaning Procedures & Residue Management 2
When determining a tank cleaning procedure for a chemical tanker, which document serves as the primary operational reference for cargo-specific cleaning requirements and compatibility?