Mastering Tank Cleaning Operations and Safety

Table of Contents

1. Introduction
2. Tank Cleaning Operations and Safety
   • 2.1 Importance of a Detailed Plan for Tank Cleaning
   • 2.2 Factors to Consider while Preparing for Tank Cleaning
   • 2.3 Purging with Inert Gas for Gas-free Tanks
   • 2.4 Determining the Safety of Tanks for Personnel Entry
3. Preparations Before Tank Cleaning
   • 3.1 Time Management and Rostering of Personnel
   • 3.2 Checking the Location, Oil Content, and Atmosphere of Tanks
   • 3.3 Preparing the Inert Gas System
   • 3.4 Taking in Water for Tank Washing
4. Tank Cleaning Operations
   • 4.1 Open Cycle Water Washing
   • 4.2 Closed Cycle Water Washing
   • 4.3 Flushing and Stripping of Cargo Tanks
   • 4.4 Cleaning Gasoline Tanks for Man Entry
5. Decanting Slops and Accounting Operations
   • 5.1 Importance of Decanting Slop Tanks
   • 5.2 Secondary Slop Tanks and Overboard Discharge
   • 5.3 Stripping and Counting of Primary Slop Tank
   • 5.4 Preventing Inadvertent Discharge of Oil
6. Measurement and Valuation of Slop Oil
   • 6.1 Determining the Density of Mixed Crude Oil Residue
   • 6.2 Measuring the Volume and Temperature of Slop Oil
   • 6.3 Sampling and Measuring the Density of Slop Oil
7. Disposition of Slop Tanks
   • 7.1 Retaining Slop Tanks Onboard
   • 7.2 Loading Cargo on Top of Slop Tanks
   • 7.3 Discharging Slop Tanks
   • 7.4 Impact on Charter Party Agreements

Tank Cleaning Operations and Safety

Tank cleaning operations on board tankers are critical in ensuring the safety of personnel and the protection of the environment. Following a good plan for tank cleaning is crucial to minimize risks associated with cargo tank cleaning, slop disposal, and personnel entry. This section will provide an understanding of the importance of a detailed plan, the factors to consider before tank cleaning, the purging of tanks with inert gas, and determining the safety of tanks for crew entry.

Importance of a Detailed Plan for Tank Cleaning

A well-defined and detailed plan for tank cleaning operations is essential from the perspective of personnel safety. The plan should outline the time required for each stage of tank cleaning, which tanks need to be washed, the lines to be flushed, and the location at sea for tank cleaning operations. It should also address the proper decanting of tank washings into the sea, adhering to MARPOL regulations. Additionally, the plan should consider work and rest hours and the rotation of key personnel to ensure they are well-rested and available during critical operations.

Factors to Consider while Preparing for Tank Cleaning

Before commencing tank cleaning, several factors need to be taken into account. Firstly, the location of the ship is significant, as tank cleaning should not be carried out in designated Marco special areas. Secondly, the condition of oil in the tank bottoms and the oxygen content in the tank atmosphere should be checked to ensure safe cleaning operations. Additionally, the temperature of the sea water should be considered to optimize the effectiveness of tank washing. Preparing the tank atmosphere by checking inert gas systems and oxygen content is essential to create a safe environment for tank cleaning.

Purging with Inert Gas for Gas-free Tanks

Purging tanks with inert gas is necessary to make the tanks gas-free for personnel entry. This procedure involves measuring the oxygen content in the tank atmosphere, opening suitable openings for purging, and purging the tank with inert gas until the hydrocarbon content is reduced to 2% or less. Purging ensures that when air is introduced into the tank to bring oxygen levels up to 21%, all hydrocarbon vapors have been sufficiently reduced and are too weak to burn in normal air. It is crucial to follow proper purging protocols to prevent the tank atmosphere from entering the flammable zone.

Determining the Safety of Tanks for Personnel Entry

Ventilation is a crucial step in determining the safety of tanks for personnel entry. Ventilation can be achieved using inert gas fans, portable water-driven fans, or compressed air-driven fans at regular intervals. The hydrocarbon and oxygen concentrations should be measured during ventilation. When the oxygen concentration reaches 21% and the hydrocarbon concentration is 1% LEL (Lower Explosive Limit) or less, the tank is considered safe for personnel entry. It is essential to maintain closed radio communication between the duty navigating officer on the bridge and the person in charge on deck during tank cleaning and gas freeing operations. The deck logbook should also document all operations.

Preparations Before Tank Cleaning

Proper preparations before tank cleaning operations are crucial for the smooth execution of the process. This section will outline the key steps to be followed, including time management and rostering of personnel, checking the location and condition of tanks, preparing the inert gas system, and taking in water for tank washing.

Time Management and Rostering of Personnel

Tank cleaning operations require careful time management and the rotation of key personnel. As these operations are hazardous in nature, personnel should be well-rested and available at critical times, such as when lines are to be flushed or equipment needs to be shifted between tanks. Proper planning of work and rest hours, along with the rotation of personnel, ensures the safety of the crew during tank cleaning operations.

Checking the Location, Oil Content, and Atmosphere of Tanks

Before initiating tank cleaning, it is essential to check the location of the ship to ensure compliance with designated Marco special areas. Additionally, the condition of oil in tank bottoms and the oxygen content in the tank atmosphere should be inspected. This step ensures that tanks are in a suitable condition for cleaning operations and reduces the risks associated with oil residues and potential flammable atmospheres.

Preparing the Inert Gas System

Proper preparation of the inert gas system is crucial for creating a safe environment during tank cleaning operations. It is necessary to ensure that the sea-chest valve remains closed until the hump has been started and there is a partial vacuum on the inboard side of the sea chest valve. The inert gas pressure of the tanks should be topped up if they are in a low-pressure state. These precautions help maintain a positive tank pressure and prevent any oil traces from leaking overboard through the sea chest.

Taking in Water for Tank Washing

Safely taking in water for tank cleaning is an essential step that should be carried out according to established procedures. The sea suction valve must never be opened until the pump has been started, and there is negative pressure on the inboard side of the valve. This ensures the prevention of oil traces in the cargo line from leaking overboard through the sea chest. The pump should be properly aligned to take suction from the sea chest, and the machine valves should be opened to clean the crude oil washing line into the cargo tanks. It is important to avoid freefall of tank washing water into slop tanks due to the risk of sparks caused by static electricity.