GTM-8.18 Gas Tanker Manual
GTM
Emergency Procedures
 Form No.: GTM-8.18
Revision: 01
Date: 15 Oct 2024
Issued by: DPA
Approved by: MD

18. EMERGENCY PROCEDURES

The following procedures are those associated with action due to a failure of plant or an emergency situation particular to gas carriers. The overall safety procedures associated with health and safety, and major hazards are included in the Safety and Environmental Manual. Reference is also to be made to the vessel’s SOPEP/SMPEP and the relevant publications carried on board as listed in SAF 18.

18.1 UNLOADING WITHOUT DEEP WELL PUMPS

Chapter 7 of the Tanker Safety Guide – Liquefied Gases must be read in conjunction with this section.

With the exception of fully refrigerated vessels and in the event of a failure of a main cargo pump the tank may be discharged using vapour pressure to transfer cargo directly ashore or to another tank, or to the suction of a booster pump. Vapour for this procedure can be supplied from another tank, produced in the vaporiser or LPG Compressor, onboard inert gas generator, or received from shore.

Discharging by displacement with vapour is a much slower process than by using deep well pumps; the actual rate being dependent upon the physical properties of the cargo, cargo temperature, gas temperature, and available overpressure.

If cargo gas is used, it is estimated that between 30% and 50% will condense out, thus lowering the discharge rate still further.

The pressure above the liquid is to be kept constant throughout the discharge, which may not be easy as the level approaches the bottom of the tank. Frequent adjustments to the discharge rate will be necessary to maintain pressure.

18.2 FREEZING (HYDRATES IN THE CARGO)

Water loaded with the cargo, or loaded into tanks which have not been thoroughly dried, can result in ice forming at the following key locations:

Problems will occur if the water has not been drained off and the cargo is cooled down below +5°C during the voyage, as it can block deep well pumps and expansion valves. Methanol injection points are located at most of the vulnerable locations, but methanol can contaminate the cargo, and in some cases, is not allowed to be used.

(a) A blocked cargo manifold filter catcher will be signalled by a high pressure drop and reduced flow. During loading, regular draining is to occur to remove water. If it is blocked by ice, the inlet and outlet valves are to be closed and the vessel pressurised with cargo or inlet gas. Warm gas can be used if necessary.

(b) A blocked deep well pump will probably need to be cleared by methanol injection if it cannot be turned. If the sump is frozen as well, this may require considerable quantities of methanol, and attention should be given to the acceptable levels of methanol-in-cargo contamination. If this method of defrosting is not successful, or methanol is not allowed, the tank will have to be unloaded by displacement with cargo or inert gas - see paragraph 16.1.

18.3 FLAMMABILITY

All liquefied gases presently transported in bulk by sea, with the exception of chlorine and nitrogen, are flammable. The vapours of liquefied gases are generally as easily ignited as those of oil cargoes. The exception to this is ammonia vapour, which requires considerably higher ignition source energy to ignite than the other flammable vapours. Statistically, therefore, fires following ammonia leakage are less likely than those with other cargoes but it would be unwise to discount thereby the possibility of an ammonia fire.

Because of the high vapour pressure and rapid vaporisation of spilled liquefied gases, the spread of flammable vapour is likely to be more extensive than in the case of a similar liquid spillage of oil. The chances of ignition following a spill of liquefied gas are thereby greater. Radiation from liquefied gas fires, because of the rapidity of vapour production, may be intense and no fire-fighting should be attempted without full fire-fighting protective clothing.

Leakage of a liquid or vapour from a pipeline under pressure will burn as a jet if ignited which will continue as long as fuel is supplied.

A particularly destructive form of vapour burn associated with the transportation of liquefied gas in pressurised containers is the BLEVE (Boiling Liquid Expanding Vapour Explosion). This arises from the rise in pressure within the container together with the weakening of the uninsulated and uncooled part of the container shell due to surrounding fire or due to radiation from the ignited vapour emission from the safety relief valve. As a result, the container suddenly splits open, releasing the pressurised liquid to atmospheric pressure. The consequent flash of liquid vapour provides fuel for a rising fireball and parts of the ruptured container may be projected apart with considerable violence. The BLEVE is a well known occurrence in road and rail transportation but has never occurred in marine transportation and is unlikely so to occur for the following reasons:

18.4 VAPORISATION OF SPILLED LIQUID

When a gas is stored as a liquid, whether under pressure or refrigeration, it will vaporise when released to the atmosphere, taking heat from its surroundings in so doing. Depending upon the liquid spilled, the spill size and whether the spill is on land or water, the rate of vaporisation and the temperature and density of the ensuing vapour cloud will vary. Almost certainly the cloud will be low lying (only methane when warmer than -100°C, ethylene and ammonia are lighter than air), will be initially cold, and will drift downwind; its occurrence will, in general, be visible as a white 'cloud' which is condensed atmospheric water vapour.

18.5 TOXICITY AND TOXIC PRODUCTS OF COMBUSTION

Some liquefied gases present toxic hazards principally if the vapours are inhaled. Four of these toxic gases, ammonia, chlorine, ethylene oxide and propylene oxide, are also irritants to the skin and mucous membrane. Incomplete combustion of hydrocarbon vapours may produce the toxic gas carbon monoxide which is found on occasion in inert gas. Combustion of vinyl chloride may produce toxic carbonyl chloride.

18.6 BRITTLE FRACTURE

Liquefied gas spilled onto constructional steel such as ship's decks not designed for low temperatures may cool this steel to temperatures where it becomes brittle. Stress already within the steel together with that resulting from differential contraction may cause fracture of the steel in the cooled areas. The resultant fractures are generally fine and unlikely to propagate beyond the cooled areas. Detailed investigations have suggested that even with shipboard spills, the integrity of the ship is unlikely to be affected and that the seepage of liquid through the fine fractures is unlikely to have any significant consequences.

18.7 COLLISION

The SOPEP/Contingency plan is to be used in the event of a collision but special considerations on board gas carriers are:

18.8 GROUNDING

The vessel’s SOPEP/Contingency Plan is to be followed for these events.

18.9 FIRE FIGHTING

The SOPEP/Contingency plan is to be used in the event of a fire but the following points must in addition be considered.

18.9.1 Cargo Area Fire

The fire may affect the cargo and increase the boil off and subsequent cargo tank pressure. Cool area by actuating water spray system. Use reliquefaction plant.

The source of fuel should be cut off and the initial attack should be with dry powder. If necessary use fixed fire fighting system - Foam, CO2, Halon ensuring area has been evacuated.

Consider:

18.9.2 Vent Mast Fire

Ignition can be caused by a lightning strike or other source of ignition when venting.

Consider:

18.9.3 Fire on Ship or Vicinity

It is the duty of any person on board who discovers an outbreak of fire to raise the alarm immediately. Thereafter they should attempt to control the fire using the nearest available appropriate means until an organised party takes over.

In port, shore assistance must be called immediately, if possible all cargo hoses should be isolated and disconnected. Bring main engines to readiness.

At sea the ship should be manoeuvred so as to minimise the risk of fire spreading. Consider stopping mechanical ventilation in affected area.

18.9.4 Extinguishing Agents

Water
Water must never be applied onto a burning liquefied gas pool since it will provide a heat source for more rapid vaporisation of the liquid and thereby increase the rate of burning. Nevertheless, water remains a prime contributor to liquefied gas fire fighting. Being freely available in most circumstances, water is an excellent cooling agent for surfaces exposed to radiation or direct fire impingement. It may be used in spray form as a radiation screen or to deflect an unignited vapour cloud away from ignition sources. In some circumstances, water can be used to extinguish a jet or column of burning gas.

Fixed water deluge systems are fitted for covering ship structures, deck tanks, and piping.

Water spray from fixed monitors or from hand held hose nozzles can provide radiation protection for personnel in their approach to shut off valves or to leaking jet or vent fires in order more effectively to deliver an attack by dry chemicals to extinguish the flame.

Dry Chemical Powder
Dry chemical powders such as sodium bicarbonate, potassium bicarbonate and urea potassium bicarbonate can be very rapidly effective in extinguishing small LNG or LPG fires. Gas carriers are required by IMO Codes to be fitted with fixed dry powder systems capable of delivering adequate powder to any part of the cargo area by means of fixed monitors and/or hand held hoses. Jetty manifold areas are also usually provided with substantial portable or fixed dry powder systems. Dry chemical powders are effective in dealing with ignited spills on deck or in manifold drip trays or in extinguishing flames torching from a pipeline flange or fracture and have been used successfully in extinguishing fires at relief valve mast head outlets. Dry chemicals attack the flame by the absorption of free radicals in the combustion process but have a negligible cooling effect. Re-ignition from adjacent hot surfaces, therefore, must be guarded against by cooling any obvious hot areas with water before extinguishing the flame with dry powder.

Inert Gas

Inert gas from combustion generators or nitrogen gas provided from insulated liquid nitrogen containers is commonly used on gas carriers and in terminals for permanent inerting of interbarrier spaces or for protective inerting cargo related spaces, such as ships' hold spaces or enclosed plant spaces on shore, which are normally air filled but in which flammable gas may be detected. Because of the comparatively low rate at which such gas can be delivered, it is not normally used for the rapid inerting of an enclosed space in which a fire has already begun. For this, high pressure bottled CO2 gas or halon is injected through multiple nozzles, the mechanical ventilation system to the space having been first shut off.

While CO2 injection systems are rapidly effective in enclosed space fire extinguishing, they have two disadvantages. Their fire extinguishing action is achieved by displacing oxygen in the space to a level which will not support combustion and it is therefore essential that all personnel completely evacuate the space before the injection begins. Secondly, the necessarily rapid injection of CO2 produces electrostatic charging which can be an ignition hazard if CO2 is injected inadvertently or as a precautionary measure into a flammable atmosphere.

CO2 or nitrogen injected into safety relief valve vent outlet risers may be used as an alternative to the external use of a dry powder screen as an effective means of extinguishing vapour fires at the vent outlet, particularly once the initial full pressure gas flow has subsided.

Foam

In general foam installations are not provided on gas carriers for liquefied gas fire fighting. However, when the vessel has the capability of carrying cargoes also covered by the IBC code, then the flag administration may require a foam installation.

18.10 PERSONAL PROTECTION

Breathing Apparatus

Breathing apparatus is required for personnel involved in firefighting, entry into hazardous areas, and in operations involving the handling of toxic or flammable gases. The equipment should be readily available and maintained to ensure that it is in good working condition. The crew must be properly trained in its use and must know the appropriate procedures for donning and using the apparatus.

It is always preferable to achieve a gas free condition in a tank or enclosed space prior to entry. Where this is not possible, entry should only be permitted in exceptional circumstances and when there is no practical alternative, in full compliance with VMS SEP 7.5.9 (g)

18.11 PROTECTIVE CLOTHING

In addition to breathing apparatus, full protective clothing should be worn when entering an area where contact with cargo is a possibility. Types of protective clothing vary from those providing protection against liquid splashes to a full positive pressure gas-tight suit which will normally incorporate helmet, gloves, and boots. Such clothing is also to be resistant to low temperatures and solvents.

Full protective clothing is particularly important when entering a space that has contained toxic gas such as ammonia, chlorine, ethylene oxide, VCM, or butadiene.

One complete set of protective clothing is to consist of:

At least 5 suits of protective clothing are supplied to the Company’s LPG ships, and these should be stowed:

When wearing protective clothing, it is important to ensure that neither the sleeves are tucked into the gloves nor the trousers into the boots. This is to avoid low temperature cargo falling into the gloves and boots of personnel working in areas where splashing of cargo or spillage is possible. Sleeves are to pass over gloves, and trousers over the boots of all protective clothing.

In some ships, the construction, size, or type may necessitate a departure from this distribution. Where this is the case, the location of equipment will be established by the Superintendent and noted in the ship’s Safety & Training Record Book.

Suitably marked decontamination showers and eyewash should be available on deck in convenient locations. The showers and eyewash should be operable in all ambient conditions.

18.12 EMERGENCY ACTION - GENERAL

Speed of response is crucial, and particular attention must be paid to Emergency Party drills and the training of substitutes.

Prior to cargo operations, dry powder hoses and fire-fighting equipment must be run out, ready for use, and sited close to the manifold being used.

The Emergency Organisation is to react according to the contents of the SOPEP/Contingency plan, except that:

18.13 ESCAPE OF GAS ON DECK

Whether a spillage of liquid or a leak of vapour, the priorities of the Emergency Party are to:

The flow of gas from a source which is between two valves on the Emergency Shut Down system will be limited. However, personnel advancing to close a valve manually close to the source of a spillage or leak must:

Care must be taken to avoid cargo coming into contact with the skin.

Any leak of LPG will produce a rapidly expanding cloud of explosive vapour, which must be prevented from coming into contact with a source of ignition. It is imperative, therefore, to isolate any source of ignition and ensure that no vapours enter the accommodation. Early consideration must be given to altering course and/or speed, and if necessary, to stopping ventilation fans. Personnel who have to leave the accommodation to close vent intakes must wear breathing apparatus and protective clothing.

If a vapour cloud approaches a known source of ignition, consideration must be given to attempting to "bend" its path by putting up a solid water wall.

The rate of dispersal of a vapour cloud will depend on climatic conditions. However, the use of liberal quantities of water in spray form will increase the rate of vaporisation, and, in the case of liquid spillage, reduce the risk of cold fractures of steel. Solid water jets must not be used on liquid spills, as they will result in splashing of cold liquid. Fixed water sprays may also assist in vapour dispersal if near enough to the cloud.

18.14 FIRES INVOLVING LPG

The highest priority of action must be given to stopping the gas flow to limit the amount of flammable material available, and contain the fire in as small an area as possible. This may happen automatically with the operation of the Emergency Shut Down System. Fire fighters must wear protective clothing and self-contained compressed air breathing apparatus. Tackling the fire requires the use of two media, water and dry powder.

Large quantities of water spray are to be used:

The normal extinguishing medium for LPG fires is dry powder, which is propelled by nitrogen. The Master is to ensure that all Officers are familiar with the operation of this equipment, and the technique to be used in fighting an LPG fire.

The best results are achieved by applying dry powder at a maximum rate by using as many guns as possible from upwind. The guns must sweep rapidly backwards and forwards over the fire area. If a liquid spillage is involved, the surface of the spillage must not be disturbed by direct impact.

Dry powder guns discharge at not less than 4 kilos per second. The initial recoil and subsequent force exerted by discharge means that in order to avoid the wastage of dry powder, a second person may be needed to help the operator maintain control of the gun.

If it is judged preferable to allow a flame to burn from a controlled leak, such as a pipe fracture, water spray is to be used to contain the fire without extinguishing the flame.

Either CO2 or Halon are fitted to the Cargo Control Room, Compressor Room and Motor Room on LPG ships.

18.15 ABANDONING THE SHIP IN THE PRESENCE OF TOXIC VAPOURS

The Master may have to consider abandoning ship in the presence of toxic gas following, for example, a collision or fracture in the loading line. For this purpose, sufficient escape breathing apparatus of 15 minutes duration are supplied for all on board.

(a) At Sea

If, during cargo operations, the accommodation becomes filled with toxic vapours (e.g. Anhydrous Ammonia) such that it is impossible for personnel to remain therein, the Master may order the ship to be abandoned, or at least to move the ship's company upwind of the source.

In this case, the Emergency Party, wearing full breathing apparatus, is to prepare the most suitable lifeboats, and lower them to the embarkation level.

When instructed, personnel and supernumeraries inside the accommodation are to put on their escape breathing apparatus and man the lifeboats with the minimum of delay. The Officer on the brake is to board the lifeboat by way of the ladder when the boat is in the water. Some types of fully enclosed boats may be lowered from inside the boat.

The lifeboat is to be manoeuvred upwind, clear of the vapour before the engine is started. This restriction may not be necessary with enclosed lifeboats. This operation is to be undertaken by personnel wearing full breathing apparatus, with their own escape breathing apparatus as standby.

Once the escape breathing apparatus has been put on, action must be swift and completed well within the 15 minutes duration of the sets.

This is a difficult operation and is only to be attempted if there are no alternatives. Whenever a suitable opportunity presents itself, the Master is to conduct exercises as outlined involving the whole ship's company.

(b) In Port

Circumstances may arise where the Master has to order the ship to be abandoned when the accommodation area is enveloped in a cloud of toxic vapour. In this case, the Emergency Party, wearing full breathing apparatus, will be responsible for indicating the route to be taken by personnel (wearing their escape breathing apparatus).

18.16 EMERGENCY SHUT DOWN SYSTEM

The Emergency Shut Down (ESD) system is a requirement of the IMO Code for the carriage of liquefied gases in bulk and is a recommendation of SIGTTO.

All members of the ship’s company must be aware of locations and the methods of activating and testing the Emergency Shut Down System specific to their vessel. The Emergency Shut Down System is a quick closing system, which may be activated automatically or manually. It will close all deck valves and shut down all cargo machinery.

ESD could be initiated by one of the following:

The initiation of ESD will lead to the following:

The emergency shut down system may comprise of two separate systems - an electrical loop with operating buttons located at strategic points on the ship and/or a pneumatic loop containing fusible plugs. The two systems may be interconnected by a pressure switch in the electrical loop.

If the electrical circuit is broken by operation of a push button, or the air pressure drops by the melting of a fusible plug, the following action is initiated:

The immediate effect of this action is to release pneumatic pressure and activate the spray system if fusible plugs have melted and the deck spray system is set to 'Automatic'.

This results in the immediate closure of all hydraulically operated valves and shut down of the gas plant.

A weekly test routine is to be established for the ESD system. The routine must ensure that all release points are tested over a monthly cycle. Test records are to be maintained in the SSTRB or PMS, as appropriate.

Testing to include portable ESD systems (umbilical) and fusible plugs locations where possible (fitted with adjacent release valve).

Activation of the ESD can create a pressure surge because of change in the rate of flow of liquid in cargo lines. The surge can be dangerous if the change of flow rate is too rapid.

Refer to LPG Manual Section 6.4.1 for further guidance.

18.17 EXPOSURE TO GAS CARGOES

18.17.1 Precautions to Avoid Exposure

During cargo operations, the number of personnel allowed on deck forward of the accommodation must be kept to the minimum. Under normal circumstances, they are to be restricted to those persons directly concerned with the loading/discharging operation.

During all cargo and gas freeing operations, the Master is to consider the risk to personnel on deck encountering a concentration of cargo vapour. If the cargo is particularly hazardous, he is to ensure that personnel working on deck carry the Emergency Life Support Apparatus.

In vessels carrying Vinyl Chloride Monomer or Propylene Oxide where there is a possibility of vapour or liquid escaping, all operations such as hose disconnection and cargo sampling will be carried out or supervised by personnel wearing full CABA and totally enclosed protective clothing.

18.17.2 Action in the Event of Exposure

The action to be taken will depend on whether exposure has resulted in:

Action in each case is similar for many types of cargo carried in LPG ships, but chemical data sheets (MSDS’s) must be checked before handling begins.

Decontamination centres and eye wash facilities are provided to assist persons who have been contaminated by cargo.

Immediate medical advice and assistance should be sought in all cases of exposure to gas cargoes.

18.17.3 VINYL CHLORIDE MONOMER

Vinyl Chloride Monomer (V.C.M.) is carried as a liquid in certain LPG ships, which have been converted or built for the purpose.

V.C.M. is a chlorinated hydrocarbon and has flammability limit of 4 – 33% by volume and toxicity characteristics similar to many cargoes of hydrocarbon origin. In addition, however, long-term exposure to high concentrations has been linked with a rare form of cancer, the TLV has therefore been set at 1 ppm – a level well below the bottom of the flammable range. V.C.M. has an odour threshold of 2000 ppm, and therefore smell cannot be relied upon as a means of detection.

It should be noted however, that to date, no cases have been recorded relating to exposure to the monomer. The only cases have been linked with production processes, and in particular to cleaning of the autoclaves used in the production of PVC.

Nevertheless, it is policy that exposure levels should not exceed 10 ppm unless suitable protection such as CABA, ELSA, and possible chemical suits are used.

Ships, which are in the VCM trade for all or part of the time, have specialised detection and protective equipment. In addition, modified emergency procedures have been developed to deal with the problems, which may arise from the presence of PVC.

Nevertheless, it is policy that exposure levels should not exceed 1 ppm unless suitable protection such as CABA, ELSA, and possible chemical suits are used.

Ships, which are in the VCM trade for all or part of the time, have specialised detection and protective equipment. In addition, modified emergency procedures have been developed to deal with the problems, which may arise from the presence of the gas.

18.17.4 PROPYLENE OXIDE

Propylene Oxide (PO) is an eserine with wide flammable limits of 2.8 – 37% by volume. The TLV of this product is 50 ppm, while its odour threshold is 200 ppm. Exposure to the liquid or high concentrations of the vapour can lead to eye burns, skin irritation and blistering, vomiting, lack of co-ordination and depression.

18.17.5 Air Supply/Air Conditioning

When certain toxic cargoes such as chlorine are carried, the IMO IGC Code requires that a space within the accommodation is designated as a safe haven or citadel. This may be the bridge or cargo control room and is required to accommodate the entire ship’s company and provide an uncontaminated supply of air for a period of not less than four hours. Easy access is to be made available from the open deck and the accommodation via an airlock which has a decontamination shower fitted close by.

It should be noted that when the accommodation air supply/conditioner is on 100% recirculation, a partial vacuum exists. It is important therefore that the double doors to the accommodation are kept shut in order to avoid gas entering the accommodation.