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4.2 Services & Treatment :
Heating & Lighting Services
4.2
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.
Perimeter seals
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.
Panel upgrades
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.
Boards
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. In
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
flames. 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
door construction.
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.
Intumescent papers
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
A typical Victorian
panelled door in a
house: upgrading to
provide half-hour
fire protection could
be achieved by the
use of intumescent
perimeter seals and
intumescent paper
to the recesses of
the panels with
minimal impact
on its character.