Brigade Order - Shropshire Fire and Rescue Service

Brigade Order - Shropshire Fire and Rescue Service
Brigade Order
Brigade Order
Operations 14
Bulk Liquid Petroleum Gas - LPG
Page No.
Characteristics of LPG
Bulk Storage Sites
Facilities for the Cooling of Tanks
Accidents at Bulk LPG Installations
Leakage of LPG with Ignition
Leakage of LPG without Ignition
Pre-planning and Training
LPG Tankers
P Raymond
Operations 14 Part 10
Section 8
Bulk Liquid Petroleum Gas – LPG
The purpose of this Section is to identify the chief risks likely to be encountered at
incidents involving leakages of liquefied petroleum gas at bulk storage installations. It
suggests the nature of operations which may need to be undertaken by the Fire and
Rescue Service in such an event; and indicates the extent to which operations may
usefully be pre-planned in consultation with management of the premises concerned.
Much of the guidance could be applied to small storage arrangements also, though
these are not specifically included. It is not intended to detail standards of fire
protection for LPG installations but mentions some of the safety measures which may
be encountered that will assist in management of the fire fighting risks and the action
which may be taken in an emergency.
Characteristics of LPG
The term liquefied petroleum gas (LPG) refers to varieties of hydrocarbons derived from
crude petroleum processes or from natural gas, being gases at normal temperature and
pressure but which become liquid with either a moderate increase in pressure or a
moderate drop in temperature, or both. (The term does not embrace such substances
as methane which, though having certain of the same characteristics is lighter than air
and therefore requires different treatment.)
These hydrocarbons include propane, propylene, butane, isobutane and butylene. The
more readily liquefiable gases of this group are commercial propane and commercial
butane, each of which may contain in varying amount several of the other hydrocarbons
The storage and transportation of large quantities of LPG in liquid form, is both
convenient and economical. Liquefaction may be achieved in two ways:
By the application of pressure in excess of the equilibrium vapour pressure; at
normal temperature (15.6°C), 1 bar for commercial butane and 5 bar for
commercial propane.
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By cooling to temperatures below the boiling point which for commercial butane
is about – 1.1°C, for commercial propane - 40°C. When liquefied in this way the
refrigerated LPG may be stored at pressure only slightly in excess of
atmospheric, provided it is continually refrigerated.
Refrigerated storage is only economical when large quantities of approximately 2,000
tonnes or more are required to be stored at one location. The usual method of storage
and transportation is as a liquid under pressure at ambient temperatures.
The density of the liquid is approximately half that of water.
Therefore, LPG if released, will tend to accumulate at low levels, hugging the contours
of the ground, filling valleys, ditches and other low lying areas. In a comparatively still
atmosphere, it will not disperse easily but can travel for long distances from the point of
release. In this respect, it differs from methane which, being lighter than air tends to
rise and disperse readily.
LPG becomes flammable when mixed with air in a concentration within the flammable
range – for butane 1.9% to 8.5%, for propane 2.2% to 9.5% by volume; values for
commercial butane and propane will not differ materially from the figures given here.
4.5 litres of butane when vaporised will produce around 1 cubic metre of gas at
atmospheric pressure at 16°C; thus, at a 5% concentration in air, 20 cubic metres of
flammable mixture would be formed.
Leaks of LPG are very likely to occur as vapour but if, at atmospheric temperature,
there is a leakage from the liquid phase of a pressure container or from a pipe-line, an
outflow of liquid butane can occur and there may be some delay in evaporation to the
gas phase. An outflow of liquid propane is also possible but, owing to its lower boiling
point, this would be more rapidly converted to gas. A leak at a flange or valve may
often be detected by the presence of hoar frost due to the evaporation of the LPG
causing a local reduction in temperature and the freezing of moisture in the surrounding
The pressure in a container is related directly to the composition of the particular variety
of LPG and the liquid temperature. In all cases, a moderate rise in temperature greatly
increases the pressure, for example, at 38°C commercial butane exerts a pressure up
to 4.6 bar and at the same temperature commercial propane will exert a pressure up to
14 bar.
Liquid LPG has a relatively high co-efficient of expansion and, therefore, a container is
filled to a limit which permits liquid expansion due to a normal rise in temperature
without danger of over-stressing the container by hydraulic pressure.
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LPG is odourless and non-toxic but has anaesthetic properties when inhaled in
quantities for a long period. Inhalation in moderate concentrations produces nausea
and headache. Heavy concentration in a pit or similar confined space may produce
oxygen deficiency and cause asphyxiation. Such concentrations would present a
serious risk of fire which might originate with explosive violence. To assist in detecting
the presence of LPG a stanching agent is added (before sale) except where the
intended use requires a gas free from odour as, for example, in the manufacture of
aerosols. The odour produced is sufficiently strong to ensure that leaks can be
detected well before the gas concentration approaches the lower limit of flammability.
Bulk Storage Sites
The storage of LPG in large quantities occurs:
At refineries and other major installations and distributing depots of the oil industry
At producer and holder stations of the Gas Boards
At the premises of some large industrial users
It is normal to plan installations upon a site with due regard to fire exposures between
containers (or group of containers) and buildings, other surrounding risks and
boundaries. The contour of the ground, as it may affect the flow of heavier than air
gases relative to roadways or other places where ignition might occur, is also a factor.
Where several containers are required, alignment across rather than along the direction
of the prevailing wind is usually adopted where site conditions allow. In the case of
horizontal tanks, these may be positioned so that the tank ends, which are more
susceptible to failure under excessive pressure, do not face towards buildings or plant.
Containers may be cylindrical tanks, both vertical and horizontal, or spheres. The
capacity of large containers is considerable; for example, spheres to accommodate
quantities of the order of 3 – 5 million litres are not unusual within the oil industry and
the capacity of a refrigerated tank may be many times greater. On most sites however,
storage requirements are met by smaller containers.
Safety fittings normally include excess flow valves at container outlets and pressure
relief devices (including, in the case of refrigerated tanks, vacuum breakers) fitted in the
crown of a pressure variation due to a normal rise in the ambient temperature.
Containers for refrigerated storage are constructed with an outer cladding to protect and
contain the insulating material, which may be of the order of one metre in thickness; the
interspace may also contain inert gas.
High standards of construction and maintenance make it unlikely that a container would
fail under normal conditions. Any major spillage is more likely to result from damage to
or failure of a valve or flanged joint on a product pipe-line.
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In order that any liquid spillage will be directed away from containers and from ancillary
equipment such as pipe-lines and valves the ground beneath containers is usually
sloped or channelled to a catchment area. At the same time, in order not to interfere
with the dispersal of gas by natural ventilation, catchments are kept as shallow as
possible consistent with a suitable degree of containment and the superficial space
available for this purpose.
Main valves are positioned where they are most likely to be accessible in an emergency
and they may also be remotely controlled.
Facilities for the Cooling of Tanks
In the event of fire, the exposure of any container to the heat will be accompanied by an
increase in the internal pressure which, unless steps are taken to cool the container,
may lead to the opening of the pressure relief devices, the involvement of gas escaping
from these positions, and a general deterioration in the fire situation resulting eventually
in a BLEVE (Boiling Liquid Expanding Vapour Explosion)
Various types of automatic water spray installations are in use which apply cooling
water to a container either through a piping system with a large number of heads
distributed over the whole of the container surface or, alternatively, over the upper parts
of a container so that a film of water spreads downwards. With the latter arrangement it
is possible that some of the lower parts of a container will be imperfectly covered but the
upper parts, most often including the gas phase which is more readily susceptible to
damage by heat, will normally be effectively protected. Any water spray systems may
also be designed for manually controlled hot weather cooling to reduce loss of produce
due to an unduly high rate of vaporisation.
On some storage sties, fixed ground monitors are provided as an alternative to or as a
supplement for water spray installations.
The need for further water supplies, for Fire Service use, is mentioned later in this
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Accidents at Bulk LPG Installations
The kind of accidental occurrence for which provision has to be made is the leakage of
LPG either as a spillage of the liquid – with vaporisation dependent upon the particular
variety of LPG and the ambient temperature – or as an escape of gas. In either event,
there is the serious risk that fire or explosion will occur, not necessarily at the initial
stage but inevitably if the escape is not arrested and the gas safely dispersed before it
reaches a source of ignition. In all cases the first consideration is to stop the outflow of
product, if possible by the closure of valves and, if ignition has occurred, to afford
immediate protection to the tanks and all surrounding risks.
Pre-planning between the Fire and Rescue Service and the management concerned,
instruction of the staff of the premises, Fire Service familiarity with the topography of the
site and exercises in which the site staff and the Fire and Rescue Service train together
are vitally important. These matters are dealt with later.
At the actual time of an occurrence, the appropriate technicians of the premises should,
whenever possible, be on hand to advise fire officers what emergency measures are
possible. Such technicians should also be fully consulted regarding action to be taken
by the Fire and Rescue Service. It is against this background of pre-planning and close
co-operation that the following consideration of certain courses of action is set out.
Leakage of LGP With Ignition
A small quantity of liquid butane or propane of small surface area will burn with a
reasonably lazy flame and for a comparatively long time, not increasing the surrounding
temperature sufficiently to increase greatly the rate of vaporisation. The larger the area
of fire, the less readily can heat be dissipated and the more intense the fire becomes.
A fire associated with a leakage of LPG should not be extinguished until the outflow has
been stopped, or as part of a precisely timed operation to enable operatives to go
forward and immediately stop the flow. If the fire were extinguished in other
circumstances, the large volume of inflammable atmosphere would form and the
unpredictability of the movement of a gas cloud would be extremely hazardous.
A large area of burning liquid may however, be reduced by the use of foam gently
applied from the edges in order to avoid disturbance of the liquid and consequent
increase in the rate of burning. Care should be taken to leave sufficient points of
burning to avoid the risk of a serious flash over.
Notwithstanding the early protection afforded by any automatic water spray installations,
an incident involving a major spillage of LPG or in which an LPG leak cannot be
immediately arrested, will almost certainly necessitate additional use of water for cooling
operations as soon as fire fighting personnel and mobile equipment reach the scene.
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In the application of water spray from portable branches, particular attention should be
given to any parts of a container surface or supporting structure not effectively covered
by the fixed installations and especially any dry areas which may be above the level of
liquid within a container. Any nearby product pipe-lines and installations structures
should be included. In the case of refrigerated storage containers, cooling to preserve
the structural integrity of external shells is equally important; external shells enclosing
the legs of spheres may be particularly vulnerable.
The utmost discretion must be exercised in the use of water on a fire involving LPG in
liquid form since the effect is to increase the rate of vaporisation and intensify the fire.
The application of a jet of water would raise a cloud of burning gas and liberate such
heat as to be extremely dangerous for persons nearby.
Water should not normally be applied to a stop valve or a safety valve at which LPG is
leaking, or to the associated piping nearby; to do so may render the valve inoperative
due to freezing.
Where liquid is burning beneath a container, the use of water spray to cover both the
fire and the underside of the container may prevent direct impingement of flame upon
the vessel and assist in burning off the liquid.
If, due to continuing exposure to heat, the stage is reached at which pressure
relief devices open, cooling operations should be massively increased in an
endeavour to lower the pressure, but if nevertheless the discharge of gas that is
on fire becomes markedly more noisy, this must be taken to indicate a dangerous
rise in pressure. It will then be imperative to withdraw all personnel from the
vicinity without delay and to this, end the early use of ground or trailer monitors
and branch holders will reduce the need for manpower in hazardous situations.
An extremely hazardous situation would arise if the contents of an LPG container
became exhausted during a fire. With the loss of internal pressure and the admission of
air, an explosive mixture would occur within the container and if flame should enter a
violent explosion will ensue. This condition is known as Boiling Liquid Expanding
Vapour Explosion (BLEVE). If the escape of LPG is from outlets near the base of a
container, this risk can be prevented where the installation includes facilities to enable
the bottom part of a container to be charged with water.
When LPG is burning only at the point of escape, the fire will go out as soon as the
outflow is stopped and any small remainder of the product has been consumed. In the
case of a large spillage however, the quantity of liquid remaining after the flow has
ceased may be sufficient to sustain burning for some time and, in these circumstances,
the protection of any surrounding risks must continue while the LPG is either allowed to
burn off or possibly assisted to do so by judicious use of water spray.
Leakage of LGP Without Ignition
The essential difference which characterises a serious leakage of LPG without ignition
is the continuing process of vaporisation to form a gas cloud of unpredictable extent and
behaviour which may be ignited by any source in its path.
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The gas itself is not visible except in heavy concentrations but the vicinity of a liquid leak
may be discerned because the fall in temperature will condense moisture in the air and
be seen as a deposit or a white fog. Neither of these manifestations must be assumed
to indicate the limits of a gas cloud which, in fact, is liable to be much more extensive.
The most effective means for determining the approximate limits of risk is by means of
an explosimeter. Such devices are normally available at major oil installations and
storage site owners.
In any escape of LPG which has not ignited, emergency operations must be directed to
shutting off the leak at source and, in the meantime, taking all possible steps to prevent
ignition and to disperse the gas safely. At some major oil installations quantities of gas
oil are available and may be used to absorb a spillage of liquid and so reduce the rate of
vaporisation and the likelihood of flammable atmosphere reaching a source of ignition.
The use of large jets of water on fog setting and directed into the air can be used to
disperse small leaks.
It may be that a sudden escape of LPG could be ignited within moments of its occurring
and so avoid the formation of a dangerous volume of flammable mixture but any such
action would need to be taken at an extremely early stage and on the decision of the
plant management. At any later stage the gas should not be ignited and therefore such
a course is unlikely to arise in the presence of the Fire and Rescue Service. A
considerable gas cloud may have formed by the time of the Fire Service’s arrival.
Fire and Rescue Service and other emergency personnel should approach from up
wind, all vehicles being left outside the area. Only in very exceptional circumstances
should persons enter the gas cloud; not withstanding the taking of precautions, the
risk of a chance ignition may be considerable and the heat due to ignition of a gas cloud
is extremely severe.
The direction and force of the wind at the time will have a large influence upon the
movement of the gas and the distance within which its concentration may be reduced
below the lower level of flammability. Therefore, whilst all potential sources of ignition in
the vicinity should be removed without delay, the most urgent consideration may need
to be given to those which are downwind of the leakage. So long as any doubt exists as
to the actual limits of the danger zone, precautionary measures should be applied over
a move extensive area than is likely to be affected.
Within this area of precautions, all vehicles and other engines should be stopped,
electrical equipment should be switched off, fires should be extinguished and the use of
other kinds of heating appliances should cease. Telephones or radio equipment should
not be used unless flame-proof. According to the proximity of other premises, roads
and other transport routes, it may be necessary to bring movement to a standstill,
prohibit smoking and evacuate the area. Steps must be taken to prevent persons from
unwittingly entering the danger zone. Special consideration should be given to the
possibility of gas accumulating at low levels, including basements where ventilation may
be poor, or following the course of ditches and similar channels.
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If any irremovable ignition source lies in the path of a gas cloud, it may be possible to
divert the gas by interposing a dense curtain of water spray. The massive use of water
sprays may also be adopted for the more general direction of the gas and to assist in
dispersing it but it may not be possible to discern the extent to which such measures are
effective. Persons engaged in these or any operations should remain outside the
danger zone, if necessary after lashing branches in position.
The most likely occasion for any person to enter the area of a gas cloud would be as a
result of the decision to attempt to stop the leak. Such a decision would normally be
taken by the management or senior staff of the premises in consultation with Fire
Officers. In these circumstances, the operatives making the attempt should be given
the utmost possible protection, including heavy coverage by water spray or fog from the
moment of their entering the area. If necessary, the branch crews providing this
coverage should in turn be similarly protected. In the rare circumstances when
personnel may have occasion to work within the area of a as cloud, breathing apparatus
should be worn.
Once the leak has been stopped, an interval of time must be allowed to elapse for the
ultimate dispersal of the gas before normal movement within the area can be resumed.
Tests for gas should be made in any basements, pits or low lying parts where additional
ventilation may be necessary.
Pre-Planning and Training
Preceding paragraphs on accidents involving bulk quantities of LPG deal with the main
contingencies in broad terms only. The success of operations at the time of the
accident may largely depend upon the adequacy of fire planning and training directly
related to each of the premises concerned. This necessitates much more than good
layout and a sufficiency of equipment for fire fighting and cooling operations, important
though these are.
Both the staff of the premises and members of the Fire and Rescue Service should
have a clear understanding of the potential hazards and in any given circumstances,
know what action must be taken at the onset and thereafter.
The arrival of the Fire and Rescue Service should be merely one phase in the carrying
out of a carefully prepared and well rehearsed combined operation, leading to the
eventual restoration of safe conditions with the least practicable damage. The closest
possible co-operation between management and Fire Officers is essential in preplanning of this Order.
It is necessary to balance the quantity and type of fire protection equipment against the
facilities for its being brought into use at each stage. For example, if the number of staff
who may be available at the time of an emergency is small, automatic installations and
good communications will be the more important. Again, if the estimated peak rate of
water usage is not immediately sufficient, the supplies which are available should be
reasonably sufficient to contain the situation during the mobilising of further supplies
from more distant sources.
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Considerations of this kind are familiar to fire officers and it is not the purpose of this
Order to suggest fire protection standards; however, it may be remarked that for fixed
water spray installations on containers, a discharge rate of 9 litres per minute per
square metre of surface area is widely accepted. Therefore when assessing the total
need of water, an allowance of this order may be made for each protected container
which could be directly exposed to heat from a fire, the requirements for the application
of water by other means being additional.
Once the details of a satisfactory emergency plan have been agreed, all persons liable
to be concerned should be instructed and trained in its application. Fire Officers and
crews must be made familiar with the premises at risk and the facilities available, and
should have a general understanding of the normal working of the installation or plant
and any special measures of control which may be possible. Company staff should
have regular training to enable them to play the roles required of them with assurance
and efficiency. Both fire crews and installation personnel should be brought together in
combined training and exercises so that their operations may be closely integrated and
mutual confidence be established.
LGP Tankers
In the event of a tanker being involved in an accident or overturned upon the road –
especially in a built up area – the situation is liable to be complicated by damage to the
tanker and by the exposure of nearby property and the public to risk. One consequence
of a tanker being overturned may be to bring pressure relief valves, which are normally
in the gas phase of the tank, below the liquid level so that liquid will be discharged
through these valves if the tank becomes heated. In all circumstances where fire
occurs, cooling should be undertaken to prevent a dangerous build up of pressure.
If the burning at a point of leakage should be accidentally extinguisher, it should be
instantly relit by means of a remotely held flame. Provision for this purpose should be
made before the necessity arises.
Where LPG escapes from a road tanker without fire, vehicular traffic should at once be
halted and all persons be excluded from the vicinity. Large jets, on fog setting and
pointed into the air should be used to try to disperse any gas. Urgent measures need to
be taken to eliminate sources of ignition around the site, special attention being given to
basements. The occupants of all buildings within the danger area should, if possible, be
evacuated and others less immediately threatened, should be warned.
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