Canister filter respirators are not suitable for use in atmospheres where the oxygen content is insufficient to support life
Training
Good training is essential in the use of this life-saving appliance. Specially marked cylinders should be used for training to ensure that in an emergency, only fully charged units are used. Cylinder pressures should be regularly checked and low-pressure cylinders should be recharged promptly.
9.9.2 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 should also be resistant to low temperatures and solvents.
It is particularly important to wear full protective clothing when entering an enclosed space which has contained toxic gas such as ammonia, chlorine, ethylene oxide, propylene oxide, vinyl chloride or butadiene.
For certain cargoes, the Gas Codes require the use of suitable eye protection.
Chapter 10
Emergency Procedures
This chapter discusses events which may follow cargo spillage and the procedures which can be adopted to protect life and property in such circumstances. While this chapter concerns both ship and terminal, reference should also be made to Chapter Six which discusses emergency precautions particularly applicable to the ship/shore interface. For more background on these matters the reader is referred to References 2.5, 2.6, 2.7 and 2.9.
10.1 THE PRINCIPAL HAZARDS
The gases with which this book is concerned are either flammable or toxic or both. Most are stored and handled at sub-zero temperatures, or under pressure or by means of a combination of the two. The main hazards are, therefore, vapour release, flammability, toxicity and the effects of sub-zero temperatures on personnel and structures.
10.1.1 Flammability
As already described in 2.20, when a gas is released to atmosphere, if within its flammable range and if exposed to a source of ignition, it will burn. Depending upon the conditions under which combustion takes place, some degree of over-pressure will occur due to the rapid expansion of the heated gas.
A liquid spill or vapour cloud burning over open water will develop little over-pressure due to the unconfined nature of the surroundings. At the other extreme, the ignition of vapour within an enclosed space will rapidly create an over-pressure sufficient to burst the boundaries. Between these two extremes, that is in cases of partial confinement such as might occur among shore plant and equipment, ignition may produce overpressures sufficient to cause substantial damage, so escalating the hazard and its consequences.
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A leakage of liquid or vapour from a pipeline under pressure will burn, if ignited, as a jet which will continue as long as fuel is supplied.
A particularly destructive form of vapour burn, associated with the storage of liquefied gas in pressurised containers, is the BLEVE (Boiling Liquid Expanding Vapour Explosion). This is described in 2.20.
10.1.2 Vaporisation of spilled liquid
When a gas is stored as a liquid, whether under pressure or refrigerated, it will vaporise on being released to the atmosphere, taking heat from the surroundings. 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 — see Table 2.5). Initially, the cloud will be cold and will drift downwind. In general, it will be visible as a white cloud which is condensed atmospheric water vapour. The characteristic of this cloud in terms of its flammability and oxygen content are discussed in 2.20 and 9.2.2.
10.1.3 Toxicity and toxic products of combustion
Some liquefied gases present toxic hazards, principally if the vapours are inhaled. Ammonia, chlorine, ethylene oxide and propylene oxide, are also very corrosive to the skin. Vinyl chloride is known to cause cancer and butadiene is suspected as having similar harmful effects.
Incomplete combustion of hydrocarbon vapours may produce the toxic gas carbon monoxide which is found in inert gas in quantities which can vary with the qualiity of combustion in the generator. Combustion of vinyl chloride may produce toxic carbonyl chloride.
10.1.4 Frostbite
Cold liquefied gas spilled onto a person freezes the skin. This effect can cause extensive frostbite to exposed parts of the body (see 9.4).
10.1.5 Brittle fracture
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Liquefied gas spilled onto ships' decks, not designed for low temperatures, may chill the steel to temperatures where it becomes brittle. Stress already within the steel, together with that resulting from differential contraction, can cause fractures in the cooled areas. The resultant fractures are unlikely to propagate beyond the cooled areas. Spills can have serious consequences and ships have been taken out of service for extensive periods for this reason. Care should be taken and appropriate drip-trays should be provided as a protection against such spillage on ships carrying the particularly cold liquids (LNG and ethylene). The area around the manifold may be sheathed in wood or glass-fibre and all refrigerated gas carriers are provided with a stainless steel, wooden or equivalent drip tray under the manifold connections.
10.2 LIQUEFIED GAS FIRES
It is not proposed in this book to deal with fires that can occur in terminal buildings, store rooms, the ship's accommodation or machinery spaces. The characteristics and methods of fighting such fires are covered elsewhere. Provided cargo containment is not ruptured, it is rare for such fires to spread to the cargo. Accordingly, this section deals only with cargo liquid or vapour fires.
10.2.1 Fire detection
On ships, the only mandatory requirement for fire detection equipment in the cargo area is the fusible elements specified in the Gas Codes. These have to be fitted in the vicinity of tank domes and at cargo manifolds. The fusible elements provide for the automatic cargo shut-down in the event of fire. However, many modern ships have fire detectors installed in motor rooms and compressor rooms.
In terminals, where storage tank and miscellaneous plant are diversely located, fire detection equipment is extensively provided. Typical locations are electrical control rooms, boil-off gas compressor houses and at cargo pumps.
Cargo-related fires may be broadly categorised as follows:—
• Jet fires from leaks at pumps or pipelines
• Fires from confined liquid pools
• Fire, from unconfined spillages, and
• Fires in enclosed spaces, such as compressor rooms
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10.2.2 Jet fires
Small leaks from pump glands, pipe flanges or from vent risers will initially produce vapour. This vapour will not ignite spontaneously but, if the escape is large, there may be a risk of the vapour cloud spreading to a source of ignition. Should a gas cloud occur, ignition should be prevented by closing all openings to hazardous areas. Furthermore, the vapour cloud should be directed or dispersed away from ignition sources by means of fixed or mobile water sprays (see 10.3.2). If ignition does occur, it will almost certainly flash back to the leak. Leaks from pipelines are likely to be under pressure and, if ignited, will give rise to a jet flame. Emergency shut-down of pumping systems and closure of ESD valves should have already occurred but, even so, pressure may persist in a closed pipeline until the liquid trapped within has been expelled through the leak. In such a case the best course of action is often to allow the fire to burn out. The alternative of extinguishing the fire has a high risk of further vapour cloud production and flash-back causing re-ignition. While the fire is being allowed to burn itself out, the surroundings should be protected with cooling water.
10.2.3 Liquid (pool) fires
Significant pool fires are not likely on the ships' decks because the amount of liquid which can be spilled in such a location is limited. The arrangement of the ship's deck, with its camber and open scuppers, will allow liquid spillage to flow quickly and freely away over the ship's side (see also 6.6.7). Prompt initiation of ESD procedures further limits the availability of liquid cargo.
Furthermore, on LNG ships, a water curtain is fitted to provide a warming flow down the ship's side adjacent to the cargo manifold. This is to limit the possibility of brittle fractures.
A liquid spillage on shore, from tank or pipeline ruptures, may involve large quantities but should be contained in bunded areas or culverts. Any ignition of the ensuing vapour cloud would then result in a pool fire. The flame height from such a fire, in the absence of wind, is as illustrated in Figure 10.1. Figure 10.1 also illustrates the effect
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