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Spill emergencies and anti-pollution measures by chemical tankers

Seagoing chemical tanker design and operational routines all aim at reducing the risk for environmental pollution. Nevertheless: accidents can happen or be caused by improper action by anyone involved on board, ashore or by other ships. Traditional thinking rules that the vessel and her cargo should be salvaged on the basis of the values they represent. With chemical and oil cargoes this is not necessarily true. It is more a matter of containing the cargo on board or by other means until the situation can be mastered with due regard to weather, shipping etc.

Spills of any size in port, due to over-fillings, hose breakage etc, should be reported to the Port Authorities at once. Keep in mind that water supplies, other water intakes local fishing, public amenities etc can be affected with enormous human and economical consequences unless immediate counteractions can be taken.

chemical tanker navigation at sea
In order to reduce the danger for minor spillages deck scuppers should be closed, drip pans arranged under hose manifold and a close watch kept when topping up the cargo tanks.

Any accidental spills in port area and how spills are to be treated must be sought from Port Authorities, who will normally take charge of a spill situation.

Common cargoes which are particularly damaging to marine life when released to the sea: acetone cyanohydrin, acrolein. Strongly negative aesthetic effects will be caused by the release of: aniline, creasote, dodecyl benzene, acrolein, acetone cyanohydrin.

The biggest risk of a cargo spill is during cargo handling operations, either because of equipment failure or improper handling procedures. Cargo spills are therefore most likely to happen in port. In the event of a spill, the following actions should be taken immediately:

• Activate the alarm.

• Stop all cargo operations and close valves and hatches.

• If alongside a berth, notify the terminal staff of the chemicals involved and possible risk posed to personnel.

• Notify local port authorities, usually through the terminal staff.

• Prohibit smoking and use of naked lights throughout the ship.

• Clear all non-essential personnel from the area.

• Close all accommodation access doors, and stop all non-closed circuit ventilation.

• Arrange for main engines and steering gear to be brought to stand-by.

The primary factor affecting response will of course be the chemical or chemicals involved, but the action to be taken depends on the circumstances of the spillage, as well as its size and location. If there is a possibility of cargo or cargo vapour entering any accommodation or engine room air intake, appropriate preventive steps must be taken quickly. As a general rule, there should be a full initial response to any spill, the emergency party wearing the appropriate protective clothing and breathing apparatus.

Safety of personnel and the ship should take priority over environmental care. If it is possible and safe to do so, the released liquid should be pumped or washed into a slop tank or other containment, or collected for safe disposal using absorbent material. However, if it is not safe or if there is any doubt, the spillage should be washed overboard with very large amounts of water. If at sea, the tanker should be manoeuvred so as to disperse the vapour away from the ship’s accommodation.

For small, localised and contained spills, it may not be necessary to implement all the action points in the ship's contingency plan. However, the master must always keep in mind the local circumstances, the nature of the chemical involved, and the potential harm to personnel, ship's structure and the environment. In most cases it is better to overreact than to delay action.

The general advice for a corrosive cargo spillage on deck is to wash the spilled liquid overboard with large quantities of water from as far away as practicable. A fog nozzle should be used and not a direct jet of water. The emergency team should wear appropriate protection, approach the spill from upwind and direct the spray of water to the edge of the spill, gradually working towards the centre. The use of water on a fuming acid and other strong acids will initially cause a vigorous reaction that will cause increased fuming. However, this will be temporary while the spillage will be dealt with rapidly. If at sea, the ship should be turned off wind.

Deck valve and pipeline fittings leakage

If leakage develops from a deck pipeline, deck valve, cargo hose or metal arm, operations through that connection should be stopped and the situation treated as an emergency until the cause has been identified and the defect remedied. Permanent means for the retention of any slight leakage at ship and shore connections should have been provided. Operations should not be restarted until the fault has been rectified and all hazards from the released cargo eliminated.

If a pipeline, hose or arm bursts, or if there is an overflow, all cargo and bunker operations should be stopped immediately and the situation treated as a cargo spill.

Tank leakage within the ship

Leakage from a cargo tank into void or ballast spaces may cause damage to materials or equipment, and may create an explosive atmosphere and a potential personnel risk. The actions to be taken may differ depending on the product involved and other circumstances such as the weather, but should as a minimum include the following:

• Identify the products involved and the risks associated with them.

• Clear the area of all non-essential personnel.

• Identify the location of the leak

• Transfer the product in the leaking tank to an empty tank, if at all possible.

• Consider notifying port and local authorities, and ship's operators.

• Commence remedial measures.

Spills in confined spaces such as pumprooms should, where practicable, be first contained and then treated and collected for safe disposal. Spills may be contained with dry sand, earth or proprietary chemicals. Acid residues can be neutralised with sodium carbonate (soda ash) or special chemicals. Untreated acid spillage must be prevented from entering mild steel areas of the ship as rapid corrosion can follow: in extreme cases the consequent hull corrosion has caused the ship to sink.

Leakages from one cargo tank to another, or multiple leakages where there is a risk of mixing incompatible chemicals, should always be treated carefully. Where time allows, expert advice should be sought as to the possible risks involved.

A non-cargo space that has had a chemical leaking into it should be treated as a cargo space, and the same precautions taken. It should be cleaned and gas freed before any attempt is made for repairs. Remedial measures should be decided upon after consultation with the operator.

It should be borne in mind that individual ship has got own characteristics and limitations may involved handling various chemical cargoes . The master and all personnel in all cases must be aware of cargo/ship information that has been given and comply with relevant safety procedures.

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