||Compartmentation: the diagram and the detail below left illustrate
the complexity of ensuring that fire cannot spread rapidly from
one part or 'compartment' of a building to another. All openings
must be taken into consideration, including those like underfloor
spaces which can be permanently protected, and those like
doorways, ducts and pipework which must be sealed in an
Fire protection within our built
environment has always been of
vital importance, not only for
life safety but also for property and
heritage protection, including business
continuity. Fire protection, used for
whatever reason, typically falls into
two categories, active and passive.
Active fire protection generally means
those installations that will actively respond
to a fire event, including detection, sprinklers
and smoke venting for example.
Passive fire protection refers to those
products that remain robust enough to resist
the passage of hot gases and fire for a given
duration, and includes architectural elements
such as doors, floors and walls as well as
proprietary sealing systems such as collars,
wraps and dampers.
Although the term passive might not
be expected to apply to products which
react to the application of heat, it is also
used to describe elements which include
intumescing materials. Such materials
react to heat, usually by expanding, to
enhance the resistance of a component to
the passage of heat, smoke and flame.
Active and passive methods of fire
protection will typically be used in
conjunction with one another to ensure that
escape routes remain tenable for a duration
suitable for firstly effective evacuation (to
comply with life safety requirements in
The Building Regulations) and secondly for
property protection (including salvage).
The determination of where escape routes
are needed and for what period they need
to be protected, stems from the The Building Regulations 2010. Recommendations on how
to achieve those minimum expectations
are given in the Communities and Local
Government (CLG) guidance, Approved
Document B (ADB).
Compartmentation is the vertical and
horizontal division of the building into spaces
and suites of spaces that can be isolated from
each other in the event of a fire. In historic
buildings, ensuring that fire cannot spread
rapidly from one part or ‘compartment’ of the
building to another can be complex since the
integrity of walls and floors cannot always
be relied on. Furthermore, during the life of
the building its use may vary considerably,
and even minor changes to the structure and fabric may impact on the integrity of
its compartmentation. Additional measures
may be deemed necessary, particularly
when a new use is proposed, or where
its heritage value has been re-evaluated
and better understood, or indeed simply
to make the building function better.
Focusing on the need to maintain the
compartmentation of a wall, doors are
common passive fire elements that typically
need to be maintained or upgraded. A door is
seemingly a straightforward piece of joinery
– it’s a bit of wood that fills a hole! However,
things are never quite that simple.
Although any closed door will have some
delaying effect on the development and spread
of a fire, for a door to be considered a fire door
(whether it is original, old, upgraded or new),
it must be proven to be capable of resisting the
effects of a standard fire test (BS 476: Part22
or BSEN 1634-1) for stipulated periods, usually
20, 30 or 60 minutes.
The requirements for fire doors are
complex. While representative examples
of intended fire door designs are required
to be tested, this is generally not an option
where existing door-sets are to be upgraded
in situ. In most cases, regulatory authorities
are willing to accept an assessment of likely
performance in lieu of a direct test result,
which will take account of performance
evidence for upgrade materials when applied
to the specific door-sets in question.
All building elements will of course
have an inherent degree of fire resistance
but without specific knowledge of products,
construction and fire resistance testing
procedures, the determination of such periods
will be impossible. For example; will a door
measuring 44mm thick provide 30 minutes
fire resistance? The answer is possibly, but
considering its thickness alone would not be
enough to assess whether its performance
will be adequate. It will also be necessary to
consider other issues such as:
- What (if any) is the amount
of bow and twist?
- Is there any leaf damage?
- Are there perimeter intumescent
seals in place?
- Are there any intumescent gaskets to
protect the ironmongery locations?
- If panelled, what are the panels made
from and how are they retained?
Even if the above sample questions are suitably
answered, it does not determine the materials/methods required to enhance performance.
If it is found that upgrading the door
may make it suitable for use as a fire door,
the next step is to determine appropriate
upgrade materials. For timber door-sets there
are many, ranging from paints and varnishes
to board materials and intumescent papers.
The type to select depends very much on the
end appearance and the door construction
itself. Not all upgrading products are all
encompassing. Consideration of ‘reversibility’
is also needed, particularly on historic door-sets
in listed buildings.
Intumescent perimeter seals are almost always
needed on timber based fire-resisting door-sets.
They sit, usually centrally, within suitable
grooves in either the frame reveal or leaf edge
and are typically encased in a PVC sleeve.
Retro-fit seals are also available which adhere
directly to the frame reveal. These seals tend
to be wider, but as they are not encased they
may only be 2mm thick.
The purpose of intumescent perimeter
seals is to expand on heating not only to seal
the opening gap and to provide a barrier to
restrict charring of the local timber elements,
but also to provide sufficient pressure between
the frame and the edge of the door-leaf to
help control leaf distortion, caused through
dehydration and char. Performance is
directly linked to the size of the edge gaps.
Evidence suggests that once gaps exceed
4mm, the performance of the perimeter seals
dramatically reduce; lowering the pressures
produced to control distortion, decreasing the
erosion resistance capabilities and limiting
their efficiency at gap filling. The physical
amount of intumescent seal used is also not
set as the larger the door leaf (height and
width), the larger is its propensity to distort
and so the greater is the need for a larger
perimeter seal. A perimeter seal alone is not
sufficient to demonstrate suitable protection.
Assuming that the edge conditions
have been bottomed out, what of the panels? Depending on their thickness
and their method of installation, panels
can be one of the weakest part of a door
construction. Upgrades are available in the
guise of boards, papers and varnishes.
||A typical Victorian
panelled door: upgrading to
fire protection could
be achieved by the
use of intumescent
perimeter seals and intumescent paper
to the recesses of
the panels with
on its character.
Over-sailing a thin timber panel with a board
material of known fire resistance (gypsum or
calcium silicate based) may well be considered
appropriate by some people. However, screw-fixing
the board over the panel on the room
side (fire risk side) would not necessarily work
if tested under the current fire resistance test
standard. Many thin (6mm) fire-rated boards
will not offer insulation and so, if used on
the fire side, radiant heat has the potential
to burn the thin panel behind and cause it
to spontaneously combust, thereby allowing
fire to spread to the non-protected side.
this case, such boards may be best fixed to
the non-risk side so that the panel burns
away, but the fire cannot then penetrate the
applied board (subject to suitable fixings
of course). Additional questions arise from
such upgrades, where there is the use of large
boards on a single door. The door becomes
unbalanced and so distortion characteristics
may not be able to be controlled by the
perimeter edge seals, causing the edge of the
door to become exploited by the hot gases and
Boards can be, and are, successfully
used to upgrade doors, but it is essential that
the board’s inherent performance is known,
and that it has specific data to demonstrate its
use as an upgrading medium on a comparable
The primary advantage of using board
products is that, although the end appearance
is not original, the upgrade is easily reversible
subject to the minor infilling of screw fixings.
An alternative would be to upgrade panels
using intumescent papers. These are thin
(1-2mm) sheets of intumescent material, often
coated on one side with a timber veneer to
match the existing timber and grain pattern
of the base door. Such sheets are typically
applied to both sides of the panel. Their
exact installation would be dictated by the
manufacturer’s test data but generally will
require the removal of the perimeter beads in
order for the intumescent to be inserted to the
edge of the panel before re-applying either new
or the existing beads. Some manufacturers
have data which demonstrates that this is
not required, but it would be advisable to
check the evidence before installing. In this
case, the intumescent material will expand
many times its original thickness, to create a
deep protective layer, which keeps the timber
panel cool. The intumescent layer also tends
to flow, helping to fill fissures within the
burning timbers to prevent the entire mass
(intumesced product and timber panel) from
falling out prematurely.
If it is feasible to remove the existing
panel, a replica could be inserted, which will
provide enhanced fire performance. Replica
panels would typically have an intumescent
sheet (1-2mm thick) sandwiched between two
thin timber faces of between 4-6mm each.
The panel would then be replaced within the
door structure using timber beads and pins.
Specific evidence of performance of such a
system would be needed.
With each of the above options for panel demonstrate performance but only for what
was tested, which would include the specimen
size. If a tested panel measured 350mm x
350mm, it would not necessarily work on a
panel where one of the dimensions exceeded
350mm. In some instances, the self-weight of
the large expanse of reacted intumescent is
enough to pull it off the door it is protecting.
Therefore, care should be taken to ensure that
the test data supports the size (and thickness)
of panel that is to be upgraded.
As with the board fixing option, panel
upgrades that use intumescent papers are
relatively easy to reverse, albeit requiring the
potential remake of beads.
are often used to
enable the retention
of structural elements
such as these cast
iron columns where
are converted. The
coating must ensure
integrity is maintained
for long enough to
evacuate the building.
Paints and varnishes are available which offer
improvements to the fire performance of
existing doors and panels. Their performance
is based on a reactive coating that protects
the underlying door/panel construction.
The paints would require several coats, in
thicknesses stipulated by the manufacturer,
which would be applied to both sides of the
door/panel. Their end appearance varies
depending on application and is
reversible if they are water-based.
performance is again linked to
dimension and door/ panel construction.
Small tested specimens would not necessarily
support the product's use on a large expanse
of panel due to increased heat experienced by
the centre of large panels, which do not benefit
from the shadowing of the perimeter beads
and stiles and rails. Similarly the existing
substrate would need to be identical to that
tested in order to ensure good adhesion of the
reactive coatings. This would certainly require
the removal of any existing paint or varnish
finish to the underlying door-set/panel.
WHOLE DOOR UPGRADES
If a door leaf is solid with no panels, but its
thickness is not consistent with that expected
for suitable integrity duration, can it be
upgraded? The answer is ‘possibly’.
Boards Boards (plasterboards, calcium based boards
etc) could be applied if they have correct test
data to support their use as an upgrade to
thin doors. But this is again dependent on
the size of the door to be upgraded. Typically
test data will support fairly standard sized
door-sets (1,982mm x 762mm) with an existing
thickness of 35mm or more if used in single
leaf configurations. In most instances, the full
boards would be located on both sides of the
door, either notched to go over the door stop
or, the leaf re-hung and the door stop moved
to accommodate the increased thickness. This
is a robust and reversible method of upgrade
but again, has size limitations.
Intumescent papers Intumescent sheets are not really appropriate
for such full size upgrades, and paints and
varnishes have limitations in terms of base
material (removing existing paints and
ensuring similar timber base to test data) and
of leaf size.
With all intumescent and board upgrades,
it is essential to understand the test data and
how it can ultimately limit the end application.
A product seen to work in one instance on a
pre-prepared specimen of limited dimensions
will not necessarily work on a much larger
scale. Care should be taken when reviewing
test data. Always remember, test evidence
is valid for exactly what was tested on the
day of test. Its extrapolation to other uses
(including size and material) can only be given
by carrying out either many tests to cover the
range, or by having an assessment produced by
a reputable fire engineer.
Intumescent materials are also used
underneath items of ironmongery, more often
for the higher integrity door-sets (60 minutes
and above) but also for lower integrity door-sets
when items are large and/or invasive to
a door construction. Unusually large hinges
blades, for example, which cross the frame
reveal, act as a path for heat to be transferred
past the perimeter intumescent seals (usually
bisected at half-hour performance). This has
the potential to char timber deep into the
frame reveal and ignite the framing on the
Bedding hinge blades on an intumescent
gasket helps in two ways, firstly the material
will cool the blade by taking heat in order to
react and secondly, to fill local fissures within
the timber to help slow down the passage
of hot gases. Bedding hinges on ‘old’ timber
where grain patterns are prominent is also
useful as a matter of course.
The provisions above are driven by
recommendations in ADB. However,
ADB is a functional document which also
enables fire engineering to be developed
to demonstrate comparable conditions.
Taking the geometry of the existing building
into consideration, it may be possible for
a qualified fire engineer to demonstrate
that the instant flashover conditions of a
BS476 (BSEN 1634) fire test would either
not be reached or would be significantly
delayed. If this is considered in conjunction
with the speed for a fire to be detected and
grow, it could be possible to demonstrate
that a full 30 or 60 minutes fire resistance
to the British Standard, is not needed. This
provides the opportunity to reduce the extent
of upgrades needed, with obvious benefits
not only in terms of costs and timescales,
but also by limiting the need for potentially
damaging alterations to historic fabric.
SURFACE SPREAD OF FLAME
Notwithstanding fire resistance, escape
routes, defined by either ADB or a prepared
fire strategy, would be expected to have
a certain level of performance to the wall
linings. This does not relate to fire resistance
(although most escape routes would also need
fire resisting properties) but to the surface
spread of flame. This relates to the speed at
which fire will propagate and spread across the
surface of a product. Typically escape routes
would need to be classified to a National Class 1(European Class C-s3, d2). Timber has
a general surface spread of flame rating of
National Class 3 (European Class D-s3, d2).
The exposed surfaces may be treated to change
the inherent classification, enhanced to meet
the Class 1 needed. This may be achieved
by the use of suitable paints and varnishes.
There are many available and unlike the
intumescent paints/varnishes, will not have
a size restriction. It only becomes necessary
to ensure that the base timber is suitable to
receive the applied paint finish.
As with all fire rated products, be it for integrity
or for surface spread of flame, test evidence
is key, as is making sure that the product
itself is sufficiently suitable and robust for the
application in question. In historic buildings,
demonstrating fire resistance retrospectively
(that is to say, for pre-existing fabric) is
therefore quite a complex issue, and should
only really be confirmed by those with suitable
experience who are able to take account of
evidence from the product manufacturer and
apply suitable determination.