Figure 10.1 Pool fire configurations
of wind in deflecting the axis of the flame and in shortening flame-length. The emissive power of a flame surface increases with pool diameter. LNG vapours burn in the initial stages with a comparatively clear flame; LPG, however, burns with a greater production of soot and, as a result, maximum surface emissive powers are lower than for LNG. Heat radiation levels from both LNG and LPG pool fires dictate that unprotected personnel must escape from the immediate vicinity as quickly as possible.
Heat radiation from a fire falls away approximately as the inverse square of the distance between the object and the flame. The human body will feel extreme pain on bare skin after only 10 seconds of incident radiation of 6 kW/m2 and will suffer severe blistering after 10 seconds exposure to 10 kW/m2. Incident radiation greater than 10 kW/m2 will quickly vaporise PVC cables and will seriously affect fibreglass lifeboats. The estimation of safe distances from a pool fire involves complex factors but, for a large pool fire, such safe distances are likely to be some tens of metres.
Because of the damage which radiation can inflict on surrounding tanks and plant, such equipment is always protected (often by insulation or by remotely operated water deluge systems). Also, the bunds and culverts where pool fires may occur are often provided with remotely operated dry powder installations. Alternatively, they may be fitted with a high expansion foam system for rapidly building up and maintaining a depth of foam to control the rate of burning.
10.2.4 Fires in compressor rooms
Enclosed spaces containing cargo plant such as compressors, heat exchangers or pumps will normally be provided with a fixed and remotely activated fire extinguishing system such as carbon dioxide. Provided no major disruption to the enclosure has occurred, these systems should be immediately effective.
10.3 LIQUEFIED GAS FIRE-FIGHTING
10.3.1 Alarm procedures
Each gas ship and terminal should have fire-fighting plans and muster lists prominently displayed. These should be carefully read and understood by all personnel. As a general guide, when a liquid gas fire occurs, the correct procedure to adopt is as follows:—
• Raise the alarm
• Assess the fire's source and extent, and if personnel are at risk
• Implement the emergency plan
• Stop the spread of the fire by isolating the source of fuel
• Cool surfaces under radiation or flame impingement with water, and
• Extinguish the fire with appropriate equipment or, if this is not possible or desirable, control the spread of the fire as above
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Raising the alarm and initial action
Fundamental to emergency procedures is how to report and how the alarm should be given to all concerned. These procedures should be developed independently for the terminal, the ship and the ship/shore system.
Procedures should warn that a seemingly minor incident may quickly escalate to one of a more serious nature. Much is gained by immediately reporting any abnormal occurrence, thereby permitting early consideration of whether a general alarm is desirable.
In the case of incidents on a ship or on a jetty while a ship is alongside, the manpower and facilities immediately available on the ship will generally make it appropriate that the ship takes first autonomous action by initiating cargo transfer ESD by the agreed safe means, alerting the terminal to provide assistance as quickly as possible and immediately putting into action the ship's own emergency procedure.
10.3.2 Extinguishing mediums
There are a number of established and proven methods for dealing with gas fires but, to be effective, the appropriate extinguishing medium must be used.
Water
Water should never be applied to a burning liquefied gas pool. This would provide a heat source for more rapid vaporisation of the liquid and increase the rate of burning. Nevertheless, water remains a prime fire extinguishing medium for liquefied gas fire-fighting. Being abundantly available, water is an excellent cooling agent for surfaces exposed to radiation or direct fire impingement. Also, it may be used in spray form as a radiation screen to protect fire-fighters. In some circumstances, water can be used to extinguish a jet of burning gas but this is not always desirable.
Fixed water deluge systems are customary for surfaces such as ships' structures, deck tanks and piping, shore storage tanks, plant and jetties, all of which can be exposed to liquefied gas fires. Such systems are designed to supply a layer of water over the exposed surfaces and thus to provide a useful cooling effect. Provided a
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water layer of some thickness can be maintained, the surface temperature cannot exceed 100°C. Application rates vary with the distance of the structure to be protected from the envisaged fire source and range from two to ten or more litres of water per square metre of protected surface.
Water spray from fixed monitors or from hand-held hose nozzles can provide radiation protection for personnel in their approach to shut-off valves. Additionally, they can provide protection when approaching jet fires in order to deliver more effectively an attack by dry chemicals to extinguish the flame.
A special application of water sprayed from hoses is to deflect an unignited vapour cloud away from ignition sources (see Reference 2.29).
Dry chemical powders
Dry chemical powders such as sodium bicarbonate, potassium bicarbonate and urea potassium bicarbonate can be very effective in extinguishing small LNG or LPG fires. Gas carriers are required by the Gas Codes to be fitted with fixed dry powder systems capable of delivering powder to any part of the cargo area by means of fixed monitors and hand held hoses.
It is also usual for jetty manifold areas to be protected by substantial portable or fixed dry powder systems. Dry chemical powders are effective in dealing with gas fires on deck or in extinguishing jet fires from a holed pipeline and have been used successfully in extinguishing fires at vent risers.
Dry chemicals attack the flame by the absorption of free radicals in the combustion process but have a negligible cooling effect. Reignition from adjacent hot surfaces, therefore, should be guarded against by cooling any hot areas with water before extinguishing the flame with dry powder.
Dry chemicals should never be used in combination with sprayed water.
Foam
High expansion foam, adequately applied to the surface of a burning liquid pool (when confined within a bunded area), suppresses the radiation from the flame into the liquid beneath and reduces the vaporisation rate. Consequently, the intensity of the pool fire is limited. Continuous application is required in order to maintain a foam depth of at least one to two metres. High expansion foam of about five-hundred to one expansion ratio has been found to be the most effective for this purpose.
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Foam applied to unignited LNG pools can reduce the horizontal extent of gas clouds because the heat input from the foam to the evolving vapour increases the vapour's buoyancy. The foam, as it breaks down into the liquid beneath, may increase the vaporisation rate. However, if the foam is stable, it can freeze at the interface and thereby reduce vaporisation rates.
Foam, however, will not extinguish a liquefied gas fire and, while effective for the above purposes, requires to be applied to a substantial depth. For liquefied gases, therefore, foam is only appropriate for use in bunded areas and for this reason is only found at terminals and is not provided on gas carriers.
Inert gas and carbon dioxide
Inert gas or nitrogen is commonly used on gas carriers and in terminals for the permanent inerting of interbarrier spaces or for protective inerting of cargo-related spaces. These spaces can include 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 carbon dioxide gas or halon is injected through multiple nozzles, the mechanical ventilation system to the space having been first shut off. While carbon dioxide injection systems are effective in enclosed spaces, 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 evacuate the space before injection begins. Secondly, the 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 outlets may be used as an effective means of extinguishing vapour fires at the vent risers. This is particularly valuable once the initial pressure flow has subsided.
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After CO2 has been injected into an enclosed space, the boundaries of the space should be kept cool — usually with water sprayed from a hose. The space should remain sealed until it is established that the fire is extinguished and has sufficiently cooled so that it will not reignite with the introduction of oxygen.
10.3.3 Training
For effective use of any of these systems, a thorough knowledge of the capabilities of each is essential. Speed in correctly tackling a fire is vital if escalation is to be minimised and life and property safeguarded. This knowledge can only be achieved by a serious approach to training by management and operating personnel alike. Training of ship and shore personnel who may have to lead a fire party should be given in shore-based fire schools where fire-extinguishing techniques can be demonstrated and practiced. The training should be consolidated by frequent exercises on board ship and in terminals and these should be realistically staged.
Proper maintenance of fire-fighting equipment is also of importance. Inspection and maintenance should be incorporated into on board and on-site training programmes and these aspects should help to familiarise personnel with the equipment and to provide them with a fuller understanding of its operation.
For further information on fire-fighting training for liquefied gas cargoes, Reference 2.21 is recommended.
10.4 EMERGENCY PROCEDURES
10.4.1 The emergency plan
An emergency can occur at any time and in any situation. Effective action is only possible if pre-planned and practical procedures have been developed and are frequently exercised.
When cargo is being transferred, the ship and shore become a combined operational unit and it is during this operation that the greatest overall risk arises. In this respect, the cargo connection is probably the most vulnerable area.
The objective of an emergency plan to cover cargo transfer operations should be to make maximum use of the resources of the ship, the terminal and local authority services. The plan should be directed at achieving the following aims:—
• Rescuing and treating casualties
• Safeguarding others
• Minimising damage to property and the environment, and
• Bringing the incident under control
Attention is drawn to References 2.5, 2.6, and 2.7 where these aspects are discussed fully from both the ship and terminal perspectives.
10.4.2 Ship emergency procedures
Organisational structure
Effective emergency response requires an emergency organisation round which detailed procedures may be developed. The international character of ocean shipping and its universally similar command structures lend themselves to the development of a standard approach in ships' emergency planning. For gas carriers this broad uniformity can be extended further to the development of incident planning. Such standardisation is of advantage since ships' personnel generally do not continuously serve on the same ship. It is also of advantage in the handling of incidents in port in that terminal emergency planning can be more effective if there is knowledge of the procedures a ship is likely to follow.
Outlined below is a suggested emergency organisational structure for gas carriers in port which has received wide acceptance. As shown, the basic structure consists of four elements:
(i) Emergency Command Centre. In port the Emergency Command Centre should be established in the Cargo Control Room. It should be manned by the senior officer in control of the emergency, supported by another officer and a crew member acting as a messenger. Communication should be maintained with the three other elements (see below) and with the terminal emergency control room by portable radio or telephone.
(ii) Emergency Party. The Emergency Party is a pre-designated group. It is the first team sent to the scene and reports to the Emergency Command Centre on the extent of the incident. The Party recommends the action to be taken and the assistance required. The Party is under the control of a senior officer and comprises officers and other suitable personnel trained to deal with rescue or fire-fighting.
(iii) Back-up Emergency Party. The Back-up Emergency Party stands by to assist the Emergency Party at the direction of the Emergency Command Centre. The Back-up Party should be led by an officer and comprises selected personnel.
(iv) Engineers Group. Some engineering personnel may form part of either emergency party. However, the Engineers Group is normally under the leadership of the chief engineer and has prime responsibility for dealing with an emergency in the main machinery spaces. Additionally, the Group provides emergency engineering assistance as directed by the Emergency Command Centre.
Incident plans
In developing plans for dealing with incidents, the following scenarios should be considered:
• Checks for missing or trapped personnel
• Collision
• Grounding
• Water leakage into a hold or interbarrier space
• Cargo containment leakage
• Cargo connection rupture, pipeline fracture or cargo spillage
• Lifting of a cargo system relief valve
• Fire in non-cargo areas
• Fire following leakage of cargo
• Fire in a compressor or motor room
10.4.3 Terminal emergency procedures
Organisational structure
When viewed from an international perspective, it is found that terminal emergency organisational structure and incident planning are less standardised than on ships. Terminal plans depend upon the size and nature of the terminal and how it is located in relation to other harbour facilities and neighbouring industry.
Whatever the nature and location of a terminal, it will require a fast-acting emergency structure under the command of a site incident controller. The incident controller should operate from a designated emergency control room. The organisation will need to be fully responsive at any time of day or night and under shift working conditions.
While always responsible for initiation and direction of immediate action in case of a major incident, the emergency organisation at a marine terminal may come under the direction of the port authority. In such cases, the port authority should have a fast-acting structure within its own emergency control centre available at all times. Here, the port authority should have means of coordinating assistance from other public services. They should also have procedures for issuing warnings to, and evacuation of, surrounding industry and population. The terminal's emergency planning, and similar port planning, should be developed together and should be exercised jointly at suitable intervals.
It is of importance, when developing procedures, to give guidance to the site incident controller on the scaling of incident severity to provide a check on when to call upon port authority emergency response personnel and services.
Incident plans
In the development of a terminal's incident plan, the following aspects are appropriate for consideration:—
• Cargo spillage or fire on board a ship alongside the jetty
• Cargo spillage or fire
• Cargo spillage or fire while loading or receiving cargo
• Cargo spillage or fire not associated with loading or receiving cargo
10.5 EMERGENCY RELEASE AND EMERGENCY SHUT-DOWN
10.5.1 Emergency shut-down (ESD) — ship/shore link
In any serious incident associated with cargo transfer, on shore or on ship, it is essential to shut-down cargo flow by stopping pumps and to close ESD valves. All gas carriers and all large terminals have a system for the rapid emergency shut-down of cargo transfer.
Where gas carriers and terminals are dedicated to each other, as in most LNG projects, terminal and ship ESD systems are linked during cargo transfer and act in combination.
In general trading of other liquefied gases, the ship and shore ESD systems are not always linked and consideration must be given to avoiding escalation of an incident by creating disruptive surge pressures at the ship/shore cargo connection by the over-rapid closure of ESD valves against cargo flow. It is preferable that in loading a ship, the terminal ESD is actuated and completes its shut-down before the ship's ESD valves close. Similarly, it is preferable during a ship discharge that the ship completes its ESD before the terminal's ESD valves close.
It is a growing practice for loading terminals to present the ship with a pendant by means of which the ship may actuate the terminal's ESD. Similarly, some receiving terminals encourage discharging ships to provide the jetty with a pendant by means of which the ship's ESD may be actuated from the shore. In any case it is desirable that the maximum cargo flow rate be limited to that which will not cause excessive surge pressure should ESD valves downstream of the cargo connection be closed, at their known rate of closure, against the cargo flow.
While the above procedures and pendant-controls may be suitable in some circumstances, they cannot always be relied upon, especially in an emergency when personnel may activate the system incorrectly. To overcome this difficulty, it is recommended that ship and shore systems be fitted with a linked system. This must be engineered to ensure the appropriate procedure is followed, no matter which party initiates the shut-down. Details of such a system, suited to LPG, are to be found in Reference 2.34.
10.5.2 Emergency release systems (ERS)
Hard arms
Hard arms for liquefied gases are normally provided with an over-travel alarm system. In most cases this is a two-zone system. An alarm is actuated when the arm approaches predetermined limits (based upon movements of the ship at the berth). At this stage the alarm may also automatically cause a safe shut-down of cargo transfer. If the arm continues its movement (in excess of the predetermined limits), a second alarm may be sounded and, if an emergency release system is provided, the arm will automatically disconnect from the ship with insignificant spillage of cargo. Such an emergency release system is fitted wholly within the lower extremity of the arm and consists of a release coupling flanked by two closely adjacent ball or butterfly valves (see Figure 5.4). On actuation of the ERS, the two valves are closed within about five seconds and, only when the valves are closed, is the release coupling tripped. The arm then swings by counter-balance, or is automatically driven, clear of the ship, leaving the outer valve attached to the ship's manifold flange.
Experience shows that when a ship, due to an excessive wind or due to wave surges, moves beyond the arm's predetermined limits, it does so rapidly. It is for this reason that the total actuation time for the ERS, including valve closure, is deliberately designed to be short. Where ERS is arranged to be fully automatic, actuation of cargo transfer ESD will occur before valve closure and arm disconnection. Where ERS is not fully automatic, or where ERS is manually initiated, procedures should ensure that cargo flow is halted before the ERS valves commence their rapid closure. Otherwise, excessive surge pressure could result (see 5.1.2).
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