Emergency procedures have to be pre-planned and ready for immediate implementation in the event of an emergency. The procedures must anticipate and cover such foreseeable types of emergencies which might be encountered at sea or in port as grounding, fire, collision and cargo spill. In each situation, the first stages of a plan should be:
• raising the alarm,
• locating and assessing the incident, the possible dangers, and action to be taken, • organising manpower and equipment.
The detailed circumstances of an actual emergency will differ in many cases from those envisaged during pre- planning; however, the standard procedures should ensure that basic action can be taken quickly and that decisions on how to tackle any additional problems can be made in an orderly and adequate manner.
Company regulations will be tailored to individual ships, and will cover organisation, preliminary action and procedures to be followed. This guide gives general advice on aspects relevant to the carriage of liquefied gas. 7.3.1 Water Leakage into Hold or Interbarrier Space
If water leaks into a hold or interbarrier space, it may damage the insulation and, in the case of a membrane tank system, result in tank wall corrosion. These spaces are normally equipped with a water detection alarm system which will indicate if leakages occur; the water should be pumped out and the leakage remedied if possible. 7.3.2 Hose Burst, Pipezvork Fracture or Cargo Spillage
This is likely to result from the effects of pressure surge, excessive ship movement, defective hoses, leaking flange packing or overfilling of tanks.
The following actions should be taken immediately:
% the alarm should be raised and the terminal informed immediately;
• all cargo operations should be stopped and all valves in the liquid line closed both on the ship and ashore as necessary;
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• all accommodation access doors should be shut and all ventilation (except closed-circuit systems) shut down; • smoking and naked lights should be prohibited everywhere on the ship, and electrical switches used as little as possible;
• if liquid spillage occurs, fire hoses and water sprays (which should always be ready for immediate action) should be used to disperse the liquid overboard and to maintain steel temperatures so that brittle fracture is avoided: water sprays from hoses can also be used to deflect a gas cloud: for this reason water spray equipment should be available in way of the manifold during cargo operations and transfer (see paragraph 7.3.3); and • appropriate fire-fighting equipment and breathing apparatus should be assembled for immediate use: the emergency parties should wear breathing apparatus and protective clothing.
7.3.3 Dispersion of Liquid Spill and Vapour Emissions by Water Spray
The best design and operational technique is to prevent liquid spillage and vapour emission incidents altogether. However, if such incidents occur existing fire-fighting water monitors and hand-held water spray nozzles can often provide a rapid and flexible means of effecting dispersion:
• by controlling the direction of the dispersion;
• by diluting the gas with air entrained in the water spray; • by heating the relatively cold gas cloud to increase its buoyancy;
• by absorbing some toxic gases which are soluble in water e.g. ammonia and chlorine.
The size of a spillage or vapour emission which can be controlled or dispersed by water spray will depend upon available fire main water pressure and the number of jet/spray nozzles which can be employed. Leakages which can generally be dealt with will be those from loading arm swivel joints, pipeline flange connections and cargo pump shaft seals. Vapour vented from a ship's mast riser due to the operation of a cargo tank pressure relief valve may also be dispersed in this way.
However, large flammable gas leakages require extreme caution in the use of water sprays as the spray may not dilute the gas to below the LFL but simply increase the volume of the premixed cloud, increasing its buoyancy and thus enhancing the likelihood of access to an ignition source. Similarly the use of water sprays may not prevent ignition: indeed, the turbulence and mixing caused by water spray may increase the flame speed on ignition. On the other hand, water spray will assist the protection of people, structures and equipment from radiation heat damage should ignition occur.
If a flammable gas cloud is to be controlled by water spray, for example to prevent it reaching a potential source of ignition, the maximum quantity of water spray available should be brought to bear as quickly as possible to redirect the gas cloud away from the ignition source. Small pipeline liquid leakages may be vapourised with water from one hose and dispersed to below LFL with water spray from another hose. It is normal practice to protect the steel deck structure of a ship by sluicing liquid spills over the side, and additional water jets can assist spill dispersal down and away from the ship's side.
7.3.4 Tank Leakage
Cargo tank leakage to the hold space or interbarrier spaces is detected by the gas detection equipment, and constant monitoring will give continuous information on the change of vapour concentration. The stability or rate of change of equipment readings will indicate the magnitude of the leakage and, together with constant monitoring of the hold or interbarrier space pressure and temperature, will enable the operator to establish the leak rate. All leakages from cargo tanks should be regarded as serious and reported immediately.
Any specific instructions for the ship should be observed, and the following courses of action should be considered:
• pumping liquid in the hold or interbarrier spaces into an undamaged tank with compatible cargo and sufficient ullage available,
• using the reliquefaction plant or other means in order to reduce the tank pressure, and therefore the static head on the leak. Care should be taken to avoid drawing air into the tank, thereby creating a flammable mixture.
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7.3.5 Emergency Discharge of Cargo at Sea
If any tank develops a serious defect at sea, cargo should be transferred to any other tank containing compatible cargo and with sufficient ullage available. Remaining cargo which cannot be transferred will need to be discharged overboard, taking into account trim, stability and stress considerations, local circumstances and the amount of cargo to be discharged.
If cargo is to be discharged, the stern line should be used. If no stern line is fitted, an extension pipe for the midship crossover should be provided, sufficiently long to extend over the side and properly supported to prevent overstressing the manifold. The extension piece should be of material suitable for the cargo, angled downwards and fitted at the end with a suitable reducer to increase the discharge velocity and to prevent liquid from coming into direct contact with the hull and causing brittle fractures.
If emergency cargo discharge has to be undertaken, the precautions listed in paragraph 7.3.2 should be observed. In addition, the following points should be considered:
• informing or consulting the operator;
• advising local authorities such as the Coast Guard;
• broadcasting a radio warning to all other ships in the vicinity;
• heading the ship so that the direction of discharge is down the relative wind, if possible, while ensuring that the vessel is free from gas clouds;
• controlling the pumping rate in such a way as to get the cargo as far as possible from the ship, and • taking any other precautions specified for the particular ship.
7.3.6 Accidents Involving Personnel
If personnel come into contact with the cargo, the emergency action specified in the data sheet for that cargo should be taken (see Chapter 9 and Appendix 1).
If personnel are overcome or affected by the cargo, the alarm should be raised and the rescue team mobilised. The agreed rescue plan should be implemented and the responsible officer informed.
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