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Fire & Explosion During Tank Cleaning on a chemical tanker

A recent case study onboard a chemical tanker revealed fatality During Tank Cleaning Operations.What has happened? A parcel size chemical tanker was in ballast voyage and was in the final stage of tank cleaning. The next cargo parcels to be loaded, included a grade requiring a high standard of Tank Cleanliness.

The Wall Wash Test taken by the ship crew upon completion of tank cleaning revealed unsatisfactory results. The ship’s crew decided to conduct a spray in the tank with methanol to achieve the required standard of WWT. This was conducted utilizing a portable air driven pump placed on top of the methanol drum on the catwalk in vicinity of the tank. The pump was connected to a PVC hose serving as the discharge hose.

chemical tanker navigation at sea
Contributing to the above operation, there was hot work on the fire line involving cutting with a grinder and welding of a pre-fabricated piece of about 1m section. No hot work permit had been issued nor any approval taken from company as required by the SMS. The senior officers of the ship and the crew working on deck were aware of both the operations involving the hot work and the tank cleaning operation.

The discharge hose connection to the pump was leaking resulting in a liquid/vapour trail reaching the source of ignition (Hot work on the fire line 29 meters abaft). Upon ignition, the fire flashed back to the area where the drum of methanol was positioned in vicinity of the cargo tank being sprayed with methanol resulting in a subsequent explosion inside the cargo tank.

damage to chemical tank bottom
Fig: Damage to chemical tank bottom

As a result of the explosion, three (3) crew members involved in the methanol spray operations were directly affected. The first crew member inside the cargo tank and a second crew member positioned on the main deck and in vicinity of the methanol drum, sustained severe burn injuries. The third crew member stationed outside the cargo tank in vicinity of the tank entrance was reported as missing and assumed fallen overboard due to the force of the explosion. The cargo tank, adjacent pair of cargo tank, the double bottom ballast tank and main deck was damaged structurally.

The search and rescue operations for the missing crew member was carried out by the Ship with sea support vessels of the regional rescue centre for the next two and half days without any success. The two (2) crew members with severe burn injuries were medically evacuated by a helicopter to the nearest hospital and subsequently to another hospital well equipped to treat burn patients. Unfortunately the crew members succumbed to their injuries after a few days of the treatment due to the extensive nature of the burns sustained.

What could be the cause?

i) Unsafe conditions – Presence of fuel (from methanol spray) & a source of ignition for combustion occurring concurrently. This completed the 3 sides of the fire triangle. The third side of the fire triangle – oxygen was available in the cargo tank, as the space was gas free prior to the spray of methanol

ii) Unsafe act – The spray of methanol & source of ignition existed due to non-compliance of procedures and operations conducted unbeknownst to the company. The company did not permit Methanol Spraying or the hot work. Hence the existing controls were violated.

Key learning’s

  1. The underlying/root causes derived as a result of this incident deal with human behaviour and each company/organization should undertake their own methods which motivates their workforce to achieve SAFETY, through compliance to their written procedures. Addressing the “Human Element,” is a long term measure and efforts taken should be continual and conducted tirelessly.

  2. Review & reinforcement of the training system should be periodically conducted to monitor its effectiveness.

  3. Consideration to Implement a separate session with senior officers to address leadership & teamwork issues, reinforce Behaviour Based System (BBS) training, and special emphasis on managing Non Compliance.

  4. Importance of intervention of an Unsafe Act - The crew working on deck at the time were aware of both, the hot work and the methanol spray operations but no attempt was made to stop either of the 2 operations being conducted concurrently resulting in a highly hazardous situation.

  5. Effective controls should be in place to increase compliance to the working procedure.

  6. In the trade practice onboard chemical tankers, it is not uncommon that the use of methanol or other chemical/detergents is undertaken to achieve the required standard of cleanliness inside the cargo tank, pipelines, cargo hoses, manifold adaptors/reducers, gauging equipment, etc. Industry publications clearly highlight and caution regarding their use due to their flammability and toxicity hazards. The spraying with Methanol is not supported due to the same.

  7. The easy availability of methanol on board the vessel attributed to this act being undertaken. As an immediate measure, the company decided to remove all flammable solvents/detergents used for cleaning of tanks, hoses and fittings. All existing stock of such solvents/detergents from the fleet has been off landed to shore facilities.

  8. A safer alternative is being sought for use, which is both non-toxic and non-flammable and tests being undertaken for the various commercially available detergents/chemicals for cleaning, achieving the desired results. This may increase the time for tank cleaning but having a safer alternative clearly outweighs the risk being taken to achieve tank preparedness utilizing flammable /toxic solvents.

Related info:
  1. Fixed and portable tank cleaning equipments
    The installation of fixed tank washing machines within a cargo tank allows an inert atmosphere to be maintained during the washing operation, and thus permits cleaning in a closed mode in compliance with port regulations prohibiting release of noxious vapours. Their installation and use also reduces crew exposure to cargo vapours and inert gas.

  2. Tank cleaning and risk with cargo contact
    Different chemicals affect the human body in many different ways. A general information and some practical advice are available in Appendix,7, of "Medical first aid guide for use in accidents involving dangerous goods" published by IMO, WHO and ILO ref (36).

  3. Practical example of solving tank cleaning problems
    Cleaning of tanks is usually the responsibilty of the ship. Tank cleaning and the cleanliness involved have different standards depending upon the previous cargo and the cargo to be loaded. But the matter can be still more complicated, as cleanliness for one and the same product may vary, depending on who the receiver is and for what purpose the cargo is finally intended.

  4. Tank cleaning fatality- case study & lessons learned
    In the trade practice onboard chemical tankers, it is not uncommon that the use of methanol or other chemical/detergents is undertaken to achieve the required standard of cleanliness inside the cargo tank, pipelines, cargo hoses, manifold adaptors/reducers, gauging equipment, etc. Industry publications clearly highlight and caution regarding their use due to their flammability and toxicity hazards.

  5. Pre-cleaning /washing of cargo tanks
    Washing between different grades of cargo is the most common reason for tank cleaning. In most cargo sequences on chemical tankers, this cleaning may consist of no more than a simple hot or cold seawater wash. A simple water wash will disperse many types of chemicals and has been found effective between clean petroleum products such as gas oil and kerosene.

  6. Final cleaning of cargo tanks prior loading
    Method of final cleaning to be used depends on both previous cargo and cargo to be loaded. As a general rule the tanks and piping shall be completely drained of water or residues before loading. The bottom of the tanks may have to be dried up with rags.

  7. Tank cleaning and posoning hazards
    Certain substances affect the tissues locally as an irritant (cashew nut shell oil) or cause grave damage to the eyes, skin or mucous membranes (e g strong acids and caustic). Other substances may be absorbed by contact to the skin without local effects (e g nitrobenzene, aniline).

  8. Testing of tanks and cargoes
    Most common tests and checks for oil and chemical cargoes include testing tank walls for cleanliness. Testing is normally carried out by independent surveyors who, according to local practice or a written agreement in the charter party, are accepted by shipper, receiver and owner.

  9. Practical tank cleaning methods for various noxious liquid cargo
    Tanks that may have contained monomer or drying oils should first be cleaned with sufficient cold water quantities to avoid polymerization of cargo residues. In some cases, it is necessary to employ tank cleaning chemicals, but their use is generally limited as it may be difficult to dispose of slops.

  10. Special tank cleaning method
    If a special method involving cleaning agents is to be used, it may create an additional hazard for the crew. Shipboard procedures should ensure that personnel are familiar with, and protected from, the health hazards associated with such a method. The cleaning agents may be added to the wash water or used alone. The cleaning procedures adopted should not entail the need for personnel to enter the tank.

  11. Determining proper tank cleaning by acid wash method
    The acid wash method is used if there is any suspicion that a cargo of aromatics may have been contaminated by a previous oil cargo. The method is also used as a check that a tank is sufficiently cleaned before loading aromatics.

  12. Supervision of all tank cleaning and gas freeing operations
    Tank cleaning is essential on-a chemical tanker, but it must be recognised as a potentially hazardous operation, and rigorous precautions should be observed throughout the process. Together with gas freeing, it is probably the most hazardous operation routinely undertaken on a chemical tanker.

  13. Disposal of tank washings, slops and dirty ballast - safe method
    During normal operations of a chemical carrier, the main need to dispose of chemical residues, slops or water contaminated with cargo will arise during or immediately after tank cleaning. Final disposal of slops or washwater should be in accordance with the ship's P&A Manual. Tank washings and slops may be retained on board in a slop tank, or discharged ashore or into barges.

  14. Cargo tank damage during pigging operations
    Blowing and pigging of pipelines at terminals poses inherent risks for the terminal and a chemical tanker. Frequent damages to tanks have occurred. If there are doubts about the shore operation or signs of problems ashore the OOW must immediately request clarification.

  15. Determining water contamination in chemical cargo
    Presence of free water in non water-soluble products can, very roughly be determined on board by warming a sample of the product in a test tube or in a bottle. Water will then collect at the bottom of the tube and can be seen after some time.

  16. Determining Sulphur contamination (sulphides) in chemical cargo
    Certain products, in particular "virgin naphta feedstock'' (petroleum naphta) are severely contaminated by minor amounts of sulphides (and also lead compounds), which poison catalysts in further processing. Previous heavy oils or dirty harbour ballast water may have left traces of sulphides in the cargo tanks.

  17. Chloride contamination in chemical cargo - how to resolve?
    Certain cargoes are very senstive to chloride contamination, in particular glycols, methanol, ethanol . The tanks should be finally washed with fresh water. However, chlorides (salt) may still be present and a check might be useful. The greatest risk for salt deposits is on horizontal surfaces.

  18. APHA (Hazen) method for determining color of very light chemical products
    A method called APHA (Hazen) is often used for very light products, defined in ASTM D-1209, viz aromatics, ketones. This colour scale is defined with an origin in 100 cc distilled water (value 0) to succesively higher values (max 500) by adding APHA-solution (a platinum-cobolt salt solution).

  19. Loading, discharging & care of Phenol - Safety guideline
    PHENOL is carried at sea in a generally pure state. As a result, it has a high freezing point of approximately 40~ 41deg C. PHENOL is also extremely dangerous when it comes into contact with the eyes or skin and can be fatal.

  20. Hazards of Phenol - safe handling of Phenol on chemical tankers.
    Phenol must be carried at temperatures within charterers instructions, typically between +50 and + 60 degrees C. Heating instructions of the Shipper or Owners must be followed to avoid protests and delays in the port of discharge. Overheating can damage this cargo. A full cargo heating log must be maintained.

  21. Handling benzene & methanol safety precautions
    Benzene is known as a strong carcinogen and known to cause leukaemia. When handling cargoes with more than Benzene concentration of 0.5%, the Master is to ensure that all personnel involved are aware of the long term hazards.

  22. Personal protective equipments for carcinogens & cyanide-like cargoes onboard chemical tankers
    A carcinogen is a substance that may cause cancer by contact or by inhalation. It is therefore essential that the highest safety precautions are taken when handling these cargoes. Access to deck areas must be restricted to duty personnel only. All accommodation doors and ports must be closed and ventilation put on recirculation. Any member of crews involved in cargo operations must wear chemical protective suits and breathing apparatus

  23. Handling ACRYLONITRILE safety precautions
    ACRYLONITRILE are high value and require sophisticated handling for safety, health and loss prevention reasons. They need careful consideration prior loading , tank coating compatibility, cross compatibility with other cargoes carried, environmental controls if required (inerting).

  24. handling ISOCYANATES safety precautions
    Product safety data sheets may be available from various sources. For safety preparation, until the specific product safety data sheet can be obtained, Chemical Data Guide for Bulk Shipment by Water (U.S. DoT), should be used.

  25. Loading, carrying & discharging of Sulphuric acid - regulatory requirements & special handling methods
    IBC code compatibility chart strictly prohibits water in adjacent compartment to Sulphuric acid as you are aware if both come in contact with each other will generate a violent reaction. It is therefore recommended that the during loading of sulphuric acid adjacent ballast tanks to be always stripped dry to the maximum efficiency of the deballasting equipment used.

Following reference publications provide useful guidance and international regulations for carrying hazardous chemicals at sea.

Our detail pages contain somewhat larger lists of resources where you may find more useful information.

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