The Role of Compartmentation in Fire Protection
E Jackman and Howard Passey
|Badly charred roof members following the passage of fire into a roof
the single largest threat to our heritage is not fire but common damp
and decay, it is usually fire which captures the headlines. For the totality
of its destruction, nothing can compete with it.
achieve the necessary protection for the occupants of the building, its
contents and its fabric, the historic building owner is faced with a bewildering
range of options all claiming to satisfy the fire safety requirements.
Unfortunately, fire safety consultants tend to specialise in particular
approaches, and it is rare to find an individual or organisation with
the expertise in all of the various options and who can offer a balanced
the options to be considered will include:
installation of alarm and detection systems
provision of fire fighting equipment
- the installation of fire suppression systems
provision of fire resistance.
of these options will have a different function and effect as described
below. In this article we shall specifically address the category of ‘passive
measures’ and in particular compartmentation issues. Many people in the
industry refer to these measures as the ‘sleeping policeman’.
ALARM AND DETECTION
warning is vital for saving lives, particularly in large rambling buildings
where there may be visitors or personnel who are unfamiliar with their surroundings.
However, apart from alerting people who may be able to bring the fire under
control, as at Windsor Castle the alarm will do very little in the short
term to prevent property damage. In this respect, the amount that it contributes
depends upon such factors as the initial detection time and rate of fire
growth, the fire brigade’s arrival time, the type of equipment they have
to hand when they arrive, their familiarity with the property and so on.
It must be remembered that fire fighters often only have water available,
which in a historically sensitive property may be as damaging as the fire
'FIRST-AID' FIRE FIGHTING EQUIPMENT
availability of equipment such as fire extinguishers on site will have a
greater role in protecting property because it can enable a developing fire
to be put out at an early stage. However, to be truly effective it needs
to be supported by staff training, as a fire extinguisher can be quite ineffective
in untrained hands. Also, the provision of hose reels may well encourage
people to stay within a burning building for longer than is sensible, so
this type of equipment is fairly controversial. Where fire fighting equipment
is to form part of the protection programme, training needs to focus as
much on developing awareness of when to stop fighting and leave, as on how
to use the equipment.
FIXED SUPPRESSION SYSTEMS
in the form of sprinklers, these systems are probably the most controversial
of the measures available where historic buildings are concerned due in
part to the inherent risk of damage that may result from the use of water.
To some degree this risk is exaggerated by the fear that sprinklers could
be triggered accidentally - by burning the breakfast toast for example.
In fact, the sprinkler head itself has to be directly exposed to the heat
of a fire before its glass phial bursts and opens the valve. Accidental
discharge is therefore almost impossible in an environment that is free
from forklift trucks and cranes.
more realistic concern is that, in a large hall, the fire would have to
be too far developed by the time the heat reaches the sprinkler in the
ceiling for the fire to be controlled, and this is perhaps the greatest
limitation of fire suppression systems. Therefore they are generally most
suitable for smaller areas at high-risk.
appearance of sprinklers also raises some concern. Consequently, conservationists
may find sprinklers aesthetically unacceptable even if they are suitable
fire suppression systems are acceptable, and historic fabric may be damaged
by the introduction of large volumes of water, a water mist system should
cavity barrier installation in a roof space at Chatsworth House, which
is designed to
give a specific integrity performance. To prevent heat
radiation igniting adjacent material, the
barrier is set back from
the roof truss, timbers passing through the barrier are protected
some distance on either side, and the roof space is kept clear
division of the building into discrete fire zones offers perhaps the most
effective means of limiting fire damage. Designed to contain the fire to
within the zone of origin, this approach provides at least some protection
for the rest of the building and its occupants even if first aid fire fighting
measures are used and fail. It also delays the spread of fire prior to the
arrival of the fire brigade.
the event of a fire within a building protected by compartmentation, the
size of the damaged area would depend upon the layout of the fire resisting
barriers within the building. Almost every building has its own natural
compartment lines which, with a little attention, are capable of providing
upward of 30 minutes protection against a fully developed fire, and often
provide an hour or more. Fire compartmentation should therefore form an
important part of any damage limitation strategy.
halls and landings would be separated from staircases to prevent a fire
from travelling vertically up the stairwell to all floors. However the
creation of new lobbies can have a devastating impact on the character
of a fine historic interior, and is often unacceptable. There also need
to be practical limitations on the number of compartment lines because
an over-compartmented building can become restrictive in its daily use.
To be effective, compartmentation does need to be planned and implemented
properly. There is no point in upgrading the fire resistance of a door
and then not protecting the plywood duct by the side of it which runs
through to the floor above, or even through to the adjacent room.
deciding upon a compartmentation strategy it is important to have full
knowledge of the voids that exist within the building: many historic properties
do have hidden voids often purely as a result of the method of construction.
It has been said, in respect of the Windsor Castle fire, that effective
fire fighting could have been achieved with explosives as much as with
water! The fire unfortunately kept breaking out ahead of the fire fighting
operation as it exploited unsealed voids.
most important elements to be upgraded are the doors, floors and walls,
penetrations through floors and walls, and cavity barriers in the roof
spaces. Some simplified guidance as to how compartmentation should be
implemented is given below.
The upgrading of floors is always considered to be a daunting task. The
general perception is that all floorboards have to be lifted and that either
a low density concrete or net supported mineral wool slab system must
be installed in every nook and cranny. In some cases this is true, but
there are many buildings that already have inherently high levels of fire
resistance, where only relatively minor improvements may be required.
In order to ascertain just what the likely natural fire resistance performance
is, it is always worth having a structural and non-structural fire safety
survey carried out before embarking on a floor-upgrading programme. Historic
floors often incorporate pugging (a dense material introduced to reduce
noise transmission between floors) and this in itself can help provide
additional fire protection.
Recent developments have shown that it is now possible to use a 4mm highly
protective membrane as a ceiling lining which can readily be over-decorated
with a conventional lining paper and emulsion paint system. If the current
fire resistance of the floor is known then the membrane can be applied
to make up any difference. Where cornices and other fine plasterwork will
not be affected, the use of a membrane may be less invasive than removing
flooring and more acceptable to a conservation officer.
The upgrading of doors to make them fire resisting is a topic in its own
right. As a general observation, however, many upgrading measures solely
address the burn-through of thin panels and the failure of ordinary glass,
but ignore their distortion in heat, which is often the primary cause
of integrity loss. This can be addressed by careful selection of pressure-forming
or gap-filling intumescent seals and perhaps also by the introduction
of additional or alternative hardware. As a result any measures used to
upgrade the panel details would not be negated by the door distorting
out of the frame.
can be a very destructive process, involving splitting panel frames and
inserting insulating materials, grooving out door edges and/or frames
to accommodate intumescent seals, or, in non-listed buildings, losing
the aesthetic look of panelled constructions by overlaying them with fire
resistant boards. However, in recent years there have been a number of
major developments in the design of face-fixed materials which make them
more acceptable, both for sealing the door edge gap and also to overcome
the risk of burn-through in the panel or in panel/stile interfaces. Some
partially insulated glasses are also available which can often fit into
existing rebates without spoiling the decor. The whole process is to be
considered as a package and proper approval should be obtained if the
system is to provide the protection required and value for money.
Sealing voids to maintain the compartmentation strategy should be performed with caution and with
an empathy for the building as a whole. It is all too easy to seal all
voids with mineral wool or even cementitious products, while ignoring
the fact that the building needs to breathe. Indeed, there have been many
occasions when the use of 'fire-stopping' (a non-combustible barrier)
has created a micro climate which has encouraged rampant wet and dry rot. The use of intumescent
systems whereby gaps can be left to encourage air movement, but which
will close up when the fire tries to exploit them has enormous advantages,
but again, getting the gap-to-intumescent ratio right is a job for the
specialist. In sealing around pipes and cables one must never forget that
these themselves will conduct heat along their length and as a consequence
improved levels of insulation may also be required. It must be borne
in mind that such insulation can in some circumstances cause cables to
overheat. Fire stopping in a heritage building needs to be done more
sympathetically than it does in a modern building.
the roof void is an absolute necessity. Even fires in modern buildings show just how vulnerable the roof
is in helping the fire to spread once it penetrates the roof void. There
are several methods by which such barriers can be built. The choice of
design will need to take into account the affect of heat radiation through
the barrier and the durability of the structure to which it will be fixed.
There is a growing
trend to use fabric cavity-barriers, but one has to be assured that the
radiation level through them is not going to be such that roof members
some distance from the barrier will not ignite on the exposed face. Non-insulating
cavity barriers may be useless if proper consideration has not been given
to the susceptibility of the structure to radiation-initiated fire spread.
Installing barriers that do not line up with other compartment lines can
also be a complete waste of time and money.
Cavity barriers should
only be installed in roof voids in conjunction with the advice of a structural
engineer who appreciates just what will happen to the structure when it
is being exposed to temperatures of 800-1,000°C.
At these temperatures even steel joists holding water tanks, for example,
have a very low level of fire resistance. Consideration should also be
given to the tolerance of such barriers to falling debris. Many materials
become extremely brittle and weak when exposed to fire, and a more robust
solution may be desirable in certain situations.
the many measures that can be introduced under the heading of ‘fire protection’,
it is the compartmentation measures and the application of valid fire
protection systems which are most effective in helping to contain the
ravages of fire at least to the area in which it breaks out. Such measures
would have avoided the total gutting of such lovely buildings as Uppark.
deciding on a compartmentation strategy, the installation and materials
need to be considered in some detail. It is easy to spend a lot of money
and achieve little, as a result of poor design and specification. The
whole strategy needs to be developed on the drawing board, drawing lines
through the building to see exactly how the strategy should be set.
good news is that many of the treatments now available are far less invasive
than they used to be. Whereas it has been normal to have to make major
disruptions to the elements being upgraded, the intelligent use of modern
materials in the full understanding of their limits of application can
mean that compartmentation is far easier to achieve than in the past.