| Section
3 - Fire Prevention 3.1
Introduction As
stated in Section 2, fire prevention has the objective
of stopping a fire from starting. Most fire prevention measures are a matter of
good housekeeping and can eliminate many of the causes of fire, but, unless the
special risks associated with food processing, freezing and storage are acted
upon, it is likely that some risk will continue to exist unless the preventative
measures are properly targeted. Each
area of activity will have special hazards associated with it, and it is the objective
of this document to help identify the hazards in each area, so that the appropriate
measures may be developed to control the risk. There
a number of likely causes of fire,
most of them accidental, but unfortunately
some are also deliberate. The
following list, whilst not being exhaustive,
identifies the most likely normal
causes of internally generated fires: a)
Faulty operation and process plant and equipment.
b) Defective electrical
equipment, including temporary lighting.
c) Hot working during maintenance,
repair or modifications.
d) Frictionally generated heat.
e) Negligent
actions of persons.
f) Spontaneous combustion.
g) Storage of products,
packaging or other combustibles close to sources of heat.
h) Smoking materials.
i) Arson (increasingly a major cause). This
list identifies the problems in general terms and many of them are discussed in
the appropriate parts of this guide. For some items the recommendations need to
be quite specific in respect of the advice given at the time of installation,
e.g. the specification and installation of underfloor electrical heater mats and
trace heating on condensation pipes, and this guide is inappropriate for this
purpose. The International Association of Cold Storage Contractors (IACSC) guide
will contain recommendations of the design/construction of such buildings. (IACSC
Guide on Design & Construction of Insulated Envelopes for Controlled Environments
(to be published by IACSC early 1997). Stores
used for certain applications will obviously contain wrapped/boxed products and
these containers will add significantly to the fire load, since they hold very
little free moisture, and cellulose packaging materials will be very dry at sub-zero
temperatures. In bulk stores the product will be stored in octobins or palletainers,
or boxed on pallets which are either/or timber of more increasingly plastic, all
of which have the potential of contribution significantly to the total fire load. The
nature of the cold store or other temperature controlled operations requires the
walls to be highly insulated. This insulation is most effective when it forms
the inner wall cladding (more likely just behind an inner wall skin) and because
of this it has an important influence on the rate of fire growth. A
small fire outbreak will produce energy and release it into the environment. Initially,
this energy will be absorbed by the exposed faces of the building structure, certainly
until the structure reaches equilibrium with the fire gas temperature, at which
point the heat exchange effectively stops. From then on any further increase in
energy release will cause the temperature in the area to increase more rapidly
until the point of flashover is reached, when all combustible materials and gases
will ignite. In
a conventional masonry building the surface will take some while to reach equilibrium,
as the initial heat absorbed will be conducted into the structure due to the relatively
high levels of thermal conduction. With
an insulated building the surface temperature of the wall lining will soon reach
equilibrium with the gas temperature, and therefore the initial heat energy will
cause a much more rapid rise in the ambient conditions, reaching the critical
flashover condition faster than in a conventional building. This effect will be
independent of the insulation used for the overall wall construction, as it is
a function of the insulation value, density and specific heat of the first few
millimetres of wall rather than the total construction, and therefore fires in
highly insulated buildings will always reach the critical conditions required
for flashover more quickly than in a conventional building. The mechanism of fire
growth and spread is complex and multi-faceted. A
secondary influence on the rate of fire growth is however related to the nature
of the insulation. It is a fact that three of the widely used insulating materials
used because of their exceptional thermal properties, their rigidity and lightweight
nature, are expanded and extruded polystyrene and polyurethane. All are forms
of plastic foam and are combustible. If the wall or ceiling is attacked by a fire
then such constructions will add to the fire load, and it is important that measures
are taken to avoid the core of the sandwich panel becoming involved too early
in developing fire. It
is important that maintenance procedures ensure that any damage to linings are
repaired, and that any holders in the structure are sealed in a manner that maintains
the original integrity of the envelope. Methods of jointing must be maintained
in good condition. As
a consequence, and because of the immense thermal and hygiene advantages that
these materials have, there is a need to adopt higher levels of housekeeping and
attention to design that may be the case in a conventional building. Flame retarded
insulation is probably more suited for the construction of composite insulating
wall/ceiling panels than untreated material. Advice is given in section 4 as to
how to retard the involvement of the insulation materials, particularly when used
as core in a sandwich panel.
3.2
Fire Prevention Measures Common To All Areas
| 3.2.1.1
Maintenance including Hot Working Many
fires in industrial buildings, and in particular in insulated buildings, have
resulted from the failure adequately to control maintenance work activity, especially
hot working. (From the 1992 Fire Prevention analysis on accidental fires, those
due to hot working processes were second only to electrical faults, displacing
smoking materials which have been the second most likely cause in the past. Fire
Prevention No. 276, 1995). Hot working covers all processes that produce heat
and includes the following: a)
Acetylene flame cutting.
b) Welding.
c) Brazing.
d) Soldering.
e) Grinding.
f) Blow lamps (soft soldering, paint stripping).
g) Bitumen
boilers (for roof sealing). Maintenance
work might also give rise to the possibility of more flammable materials being
present, such as paints and cleaning fluids, than would occur during normal work.
It might also be the case that portable space heaters are used. It is important
the equipment, procedures and materials to be employed for such work are agreed
prior to its commencement in order to minimise the fire risk. Where the hazard
cannot be significantly reduced, a permit to work system will be needed. The purpose
of the permit is to ensure that the area is made as safe as possible before any
hot working starts, that precautions continue to be taken whilst the work is in
progress, and that the area where the hot work was carried out, and the area surrounding
are monitored for at least one hour after completion of the work. Management responsible
for repair, maintenance and modifications to buildings and plant are responsible
for drawing up the permit to work procedure, and ensuring that it is complied
with. Further advice on permit to work system is given in the HSE leaflet IND(G)98(L)
and in the LPC recommendations for hot working. (Loss Prevention Council RC7 -
Recommendations for Hot Work). | Recommendations: •
Avoid hot working, wherever practical. •
When hot working is unavoidable the permit system shall be used. •
The use of portable space heater should be considered as 'hot working'. •
All maintenance personnel shall be fully briefed as to the hazards that exist. •
Taking account of all the health and safety risks, wherever possible non-flammable
liquids or liquids with a high flash point should be used. The use of liquids
with a flash below 32°C should be subject to a permit to work system. •
Where panels incorporate combustible cores hot working shall not be performed
on the panels or any conductive component passing through the wall. e.g.. metal
pipes and ducts, in contact with the combustible core. •
When hot work in unavoidable in a zone within 1 metre horizontally of a wall
which incorporates combustible materials and/or vertically above a sandwich panel
ceiling, the construction shall be suitably protected by boards or linings, that
are able to resist the possible ignition arising from the hot working, particularly
the needs of uncapped panels. It is also advisable that an operator, equipped
with a fire extinguisher, should be present. •
Flame retardant fabrics or films are not suitable as protection against hot working. •
Particular attention should be given to the protection of insulation around insulated
pipes in the roof space or other unseen areas. |
|
3.2.1.2
Maintenance of Electrical Supply
& Electrical Appliances Including
Lighting Electrical
faults are a major cause of fires in all building types. Whilst appearing inert
and non-hazardous, electrical supply wiring can suffer from arcing as result of
loose wires or chaffed or otherwise damaged cable insulation's, and this produces
a very high, but very localised, heat source. If arcing occurs adjacent to combustible
materials it can cause ignition, and safety measures need to be taken. All equipment
must be correctly installed, and when installed it needs to be subsequently inspected
and maintained. Exposed wiring requires more frequent inspection than concealed
wiring, particularly if it is not armoured or otherwise protected. The
Electricity at Work Regulations 1989 describe the Health and Safety at Work requirements.
Compliance with the Institute of Electrical Engineers Wiring Regulations BS7671:1992
should ensure safety. When routing cables in buildings of sandwich panel constructions,
all wiring needs to be run through dedicated routes, e.g.. trunking, and must
not have direct contact with the insulation. A
second major consideration is the overheating caused by overloading of the circuits
due to the excessive power taken off. Multi-adapter plugs are a common cause of
overload. Before installing any electrical equipment, it is important to ensure
that the circuit is able to take the demand without overheating, and this is particularly
important in the case of portable equipment designed for continuous or prolonged
operations. When extension leads are in use they should be used in accordance
with good practice. Fixed wiring to, and within, process control panels can be
overlooked during routine maintenance, but this can cause fire and needs periodical
examination. | Recommendations •
Install and maintain electrical equipment in compliance with the Electricity at
Work Regulations 1989 and the current edition of the IEE Wiring Regulations using
competent persons. •
The use of temporary or portable electrical equipment shall be approved by management
and subject to a permit to work system. •
Wiring should run in dedicated trunking avoiding contact between insulation and
plasticised PVC cables. •
All cables running through insulation shall be appropriately de-rated. •
Wiring should be routed to minimise the number of holes required in any sandwich
panels forming a wall or ceiling, and also to reduce interference with the insulation
core of a sandwich panel. •
Where wiring has to pass through walls or ceilings the recommendations of Section
4 should be considered. •
All lighting shall be low temperature, e.g. fluorescent or suitably protected
where combustible material or containers are stored below; in order to avoid contact. •
The lighting units shall not compromise the fire separation function of fire rated
ceilings nor allow fire to attack the core of combustible cores panels prematurely,
i.e. before the core would become involved by other routes. •
All power circuits shall be protected by residual current circuit breakers. •
Extension leads shall be unwound in use and wandering leads shall be protected
from heat and chaffing. •
Control panels should be subject to periodic examination and maintenance. |
| 3.2.1.3
Frictionally Generated Heat Equipment
that has linear or rotational movement, and which is used on a continuous or nearly
continuous basis, will incorporate bearings, or bearing surfaces, that provide
low levels of friction when operating correctly. Should these bearings dry out
or become contaminated with higher friction materials, then the movement will
generate heat which can lead to eventual seizure. Bearings that get heated to
red heat as a result of friction are able to ignite combustible materials, with
which they may be in contact. | Recommendations •
Bearings or bearing surfaces or continuously operating equipment should be
lubricated continuously or at regular intervals and inspected regularly. (Manufacturers
instructions should be consulted). •
All moving parts shall be kept clear of combustibles. •
Where practical, bearings that are at risk due to duration, speed or load should
be monitored for temperature rise. |
| 3.2.1.4
Smoking Related Risks As
this procedure covers the food processing, and storage industry, all critical
areas will be subject to a no smoking policy. In non-hygiene critical areas a
supervised smoking policy may be introduced. Illicit smoking may take place when
there is a total ban, resulting in less careful extinguishing of smoking materials
due to an absence of suitable receptacles such as would be provided in a smoking
area. Visiting staff, i.e. contractors and delivery drivers, need to be made aware
of the smoking policy. | Recommendations •
On site smoking bans should be established and implemented. •
Where this is impractical, smoking shall only be permitted in designated areas,
suitably furnished with ashtrays, sand buckets, extinguishers etc. and kept clear
of combustible waste. •
Designated areas shall be conveniently positioned near fire alarm call points. •
Management shall be vigilant for evidence of illicit smoking. •
Violations should be severely dealt with. |
| 3.2.1.5
Spontaneous Combustion There
are many recorded cases where stored products, particularly those rich in oils,
have been the cause of a fire, due to self-heating. The conditions needed to create
an unstable environment are not easy to identify, but in most cases a thermal
'trigger' is required to raise the temperature sufficiently for an exothermic
reaction to start. Chilled or frozen products will have a much lower tendency
to self-heat than room temperature products. The 'trigger' may be a steam pipe,
space heaters or even lighting (see 3.2.1.2 above). |
Recommendations •
Management shall be fully conversant with any self-heating tendency of the
products stored, and take precautions to prevent possible spontaneous combustion. •
Special consideration shall be given to crumb and batter residue which is vulnerable
to self-heating. |
| 3.2.1.6
Arson It
is a regrettable aspect of modern life that deliberate ignition is now a major
cause of fires. Some facilities are more likely to be the subject of a third part
generated ignition than others, depending upon the product being processed or
stored. Sites
specialising in vegetable processing and storage are at a lower risk than those
handling meat products. In addition it needs to be borne in mind that all facilities
may be vulnerable to deliberate ignitions by dissatisfied or recently dismissed
staff. Access will frequently need to be restricted. There
is a greater risk when easily ignited, combustible materials are stored close
to the perimeter of a building. Delivery vehicles could be an arson target and
this should be recognised when parking. External
lighting will deter the potential arsonist. |
Recommendations •
Restrict access to all sites including the outer face of perimeter walls formed
from sandwich panels. •
Restrict access to plant rooms and stores. •
Where perimeter panels incorporate combustible cores the wall should be protected
to a height of 1.5m with masonry construction. •
Avoid storing refuse containers and combustible packaging, e.g. pallets, within
6m of the external walls of buildings, especially adjacent to openings. •
External storage should be secure. •
Except when loading/unloading, delivery vehicles would be parked remote from the
building and preferably in a secure compound. •
Surveillance equipment should be sited to help reduce the risk of undetected arson. •
External lighting, either permanently on, or triggered by motion sensors,
should be used as a deterrent. |
3.3
Fire Prevention Measures for Specific Risks
| 3.3.1
Bulk Store Handling Equipment A
significant risk associated with cold stores storing bulk product or pre-packaged
products in large quantities is that associated with fork lift trucks, since most
trucks are powered by electricity, and these require large batteries to be regularly
charged. Battery
charging is a relatively high fire risk process, and should be carried out with
this understanding. The act of charging batteries produces flammable gases, and
it is important that these are not allowed to build-up. The area used for charging
needs to be well ventilated. Connecting and disconnecting power supply cables
can produce sparks, and it is important that the recommendations of the truck
or charging equipment manufacturer are followed when charging batteries. |
Recommendations •
It is safer if all batteries are charged in a separate, well ventilated building
of conventional construction. •
Where a 'cold truck' policy operates then: - Batteries should be removed to a
separate area for charging. Where charging takes place within a store, then the
separated area shall be constructed to a 30 minute fire resistance standard. •
The chargers should be at least 1.5m from the face of the panels.
|
| 3.3.2
Cold Stores Cold
stores are a low hazard area with respect to fire occurring, and with very little
in the way of equipment or processes which produce a fire risk. However, should
the contents of a cold store become involved in a fire, the consequences in terms
of losses and fire load are likely to be serious. Doors
to cold stores are normally heated around the perimeter to prevent ice building
up in the door to frame gap. Whilst these heaters present no different fire risks
than any other form of electrical equipment, they are located in an area that
is vulnerable to damage and they are generally close to insulation, which, if
it is of a combustible nature, may cause rapid fire growth, in the event of a
malfunction in the heating tape. |
Recommendations •
Provide protection to door edges by 'buffering' the traffic to avoid damage
to heating tapes. •
Any damage shall be reported immediately. •
All doors should be inspected rigorously and frequently. •
Heaters, heating tape or connecting wiring should not be in direct contact with
any insulation. •
Heating tapes should be low voltage, transformed down from the mains supply, or
of a self-limiting variety. •
Electric cabling for use in cold stores should be suitable for the installed environment.
Note: Cabling schedules will detail grades suitable for the environment. |
| 3.3.3
Retail Outlet Cold Rooms The
risk of fire in these walk-in cold rooms is very low, other than possibly due
to electrical faults. However, both the structural and fire behaviour of these
cold rooms would be compromised if significant loads were to be placed on the
roof. Note:
It should be noted that the risk of fire in the remainder of the retail outlet
is comparatively high. | Recommendations •
Prevent storage on top of small cold stores by suitable barriers unless a
special mezzanine floor is constructed with an air gap between it and the store.
|
| 3.4
Fire Detection Early
warning, early first aid fire fighting, and early attendance by the fire brigade
all help to reduce the size and severity of the fire. Since Cold Stores/food processing
plants are occupied, although not mandatory, the premises may generally be expected
to have automatic fire detection installed. There is no need for such detection
systems to be linked directly to the local fire service, but in all premises where
a fire incident can rapidly become a serious fire the automatic call out system
would help. As stated previously, the larger buildings covered by the scope of
the document do run the risk of becoming serious fires due to the volume of the
stored product. Manually
operated warning systems are not suitable for storage buildings which are unmanned
for many hours at a time. Fire
detectors vary in respect to the way they detect a fire. The common type are heat
detectors including rate of heat rise detectors, smoke detectors, as well as ionisation
and optical beam types (infra-red). These are all suited for different fire situations,
building types and risks. Similarly detection systems can have different objectives
ranging from the minimal coverage to give life safety (type L) to those giving
life safety and property protection across the board (type P). The
BSI Standard allows a number of options as to the level of detection that an automatic
system should provide. Legislation will normally be satisfied by a suitably designed
L3 system aimed at detecting fire in escape routes. However, because of the potential
rate of fire growth in insulated buildings (see 3.1), it is recommended that,
even for life safety purposes, the system should at least comply with that required
for L2 systems, particularly targeting those areas with a fire risk such as food
processing. These must be considered to be the minimum levels. Because of the
very high potential losses, and the propensity of large storage buildings to suffer
serious fire damage, regardless of the materials used in the core of any sandwich
panels used in their construction, this document recommends an automatic detection
system complying with not less than the P2 specification for those areas where
a risk can be identified. This can be reduced to a life protection cover of L2
in cold or chilled stores separated from risk areas by proven fire resisting construction.
| Recommendations •
Except for cold or chilled stores that are separated from risk by fire resisting
construction or by at least 4m separation, detection system of P2 specification
is recommended. •
In separated or protected cold or chilled stores a system complying with L2 should
be adequate. •
Manually operated warning systems are generally unacceptable in frequently unmanned
storage areas. •
Regular maintenance and checking should taken place, especially of stand-by power
supplies/batteries. |
3.5
Extinguishing & Suppression Systems
| 3.5.1
Hose Reels and Portable Extinguishers Fire
safety legislation requires the provision of sufficient first aid fire fighting
equipment, in the form of extinguishers, to provide for personnel safety and to
help prevent the minor event causing a major fire. Because of the serious consequences
of a fire in these premises, hose reels are recommended in addition to sprinklers
in critical, but suitable areas (see EN 5306:Part 1). The subzero cold stores
present a problem for normal hydraulic hose reels and water based fire extinguishers,
as they cannot be fixed, or stored within such areas. Guidance as to the most
appropriate system will generally be given by the authority responsible for enforcing
the relevant requirements. In
cooking areas, fryers and ovens will need special consideration if they are not
covered by automatic extinguishing systems. In the case of frying equipment, it
is likely that the oil used for frying will be the material first ignited. Water
cannot be used for such fires unless it is in a finely divided form, i.e. a mist,
because of the risk of spreading the burning oil. Fires in frying equipment are
classed as type B fires, and either CO2 or foam will be needed. CO2 may be the
favoured system for hygiene and environmental reasons, although if any solid material
is involved, e.g. crumb or product, then a system such as water mist may be preferred
as it should cool the equipment as well. In the case of ovens, the fire will invariably
involve overheated product. This could be considered as a class A fire, but, due
to the likelihood of electricity being present, water is not appropriate, and
extinguishing should be by means of foam or CO2 extinguishers, depending upon
how easy it is to get the material into the oven. Advice
on assessing the number of systems required, particularly where frying and baking
takes place and where no automatic system is incorporated, is given in BS5306:Part
3. It would be safety to err on the side of caution when making the decision. |
Recommendations •
Portable extinguishers should be installed in compliance with BS5306:Part
3. •
The additional installation of hose reels in accordance with BS5306:Part 1 should
be considered, taking into account the environment. •
In low temperature environments, specially formulated water and foam extinguishers
are required. •
Do not use portable water based extinguishers near fryers or electrical ovens.
CO2 or multi-purpose foam extinguishers are recommended. •
The lack of cooling provided by CO2 or foam shall be taken into account when assessing
the risk and selecting the number and type of extinguishers. •
Areas where CO2 may be used are to be adequately ventilated. •
Adequate numbers of extinguishers need to be provided to deal with an anticipated
fire. |
3.6
Fixed Fire Suppression Systems
| Automatic
fire protection systems come in a number of types, water based sprinkler systems
or water mist, gaseous foams or dry powder systems. Most areas within a food processing/cold
storage facility generally constitute a low fire risk, and the need for automatic
protection is therefore not great. The exceptions are those areas where cooking
takes place, and where there is a greater fire risk such as machinery rooms, workshops,
transformer, switchgear and battery charging areas. The size of the space and
the volume/surface area of the burning items normally dictate whether automatic
non-water based systems can be used. Special consideration apply to the systems
can be used. Special considerations apply to the installation of total gas flooding
extinguishing systems, see EN5306:Parts 4 and 5. It is impractical to try and
fill a large area or building with an inert gas such as CO2. In
larger areas, only water based systems are suitable. When automatic extinguishing
systems are built into cooking equipment the need for sprinklers is much reduced
in these areas but the use of sprinklers, especially if built-in protection is
not present, must remain the decision of the facility owner(s)/manager(s). If
sprinklers are fitted in a food area any fryer must be covered to prevent the
water spray reaching the hot oil/fat. Sprinkler
systems are suitable for use in 'chilled' or ambient stores, if they do not compromise
other requirements. Where
the rooms are running at subzero temperatures, water based sprinkler systems present
a problems. All pipe-work and sprinkler heads must remain dry, only to be charged
with water as a result of fire being detected by an automatic detection systems.
Even in this situation the effect of water running along branch pipes at -30°C
is unknown. This is particularly so if the run of pipe is long, as is required
to give coverage in some of the High-Bay racking facilities, where the heads need
to be installed at varying levels between the stacks to be the most effective. |
Recommendations •
Automatic, water based sprinkler systems should be considered when setting
the fire safety strategy for food processing areas where cooking is taking place.
When installed, water from sprinklers should not be allowed to contact hot oil,
hot fat or electrical equipment. •
When sprinklers are fitted all voids should be protected. •
In chilled or ambient stores sprinklers could make a significant contribution
to fire control but hygiene problems may require special installation methods. •
The low risk of fire in cold stores and chilled areas does not generally warrant
sprinklers, if other aspects of this document are complied with. •
The use of sprinklers in cold stores is only recommended when the problems associated
with their use at below -20°C are fully considered and compensated for. Typical
problems may be the instantaneous icing up of access points such as doors. In
addition, structural problems may be caused as a result of rapid increases in
vapours pressure following the initiation of suppression measures. •
For High-Bay stores the installation of sprinkler systems shall follow the recommendations
for such facilities (including dual water supply). •
To ensure satisfactory performance of sprinklers an adequate water supply shall
be guaranteed. •
Note: In some areas, water supply companies may have reduced the water supply
pressure to an extent where the operations of the sprinkler systems may be affected,
if it is direct main supplied. Hence users are advised to have the sprinkler water
supply checked by the sprinkler manufacturer/installer. | |
