Memorandum by Fire Safety Development
Group (TAB 23)
The Fire Safety Development Group was created
in 1992 as a consortium of companies in the passive fire protection
field. It is committed to advancing the case for consolidating
fire safety in the built environment. Its members manufacture
a range of products used to provide structural fire protection
for all types of buildings, both in the UK and internationally.
The FSDG welcomes the opportunity to respond
to this inquiry.
Expertise we are able to offer the inquiry relates
to the Sub-committee's intention to examine the sustainability
of tall buildings. Appropriate structural fire safety measures
determined at design stage are essential to a building's durability,
environmental performance, flexibility and occupancy. This is
particularly important in developments that are concrete- and
steel-based, materials often used to construct tall buildings.
We have therefore decided to comment in the
main on this area of examination. Some of our comments have been
inevitably influenced by the collapse of the World Trade Centre
in New York on 11 September 2001.
The fire protection of tall buildings presents
a special challenge to designers and manufacturers of fire protection
products and requires a number of aspects of fire safety to be
considered. These include:
1. Structural fire protection
2. Means of escape of the occupants whether
they are able-bodied or suffer from a physical disability
3. Means of access for the fire brigade
In this submission, we will only deal with the
first item because items 2 and 3 are design issues and our members
do not have sufficient experience in these matters.
The fire protection of the structure of a building
is termed structural fire protection. It is primarily to prevent
building collapse and to provide sufficient time for occupants
to exit the building in event of a fire. It is also to ensure
that fire fighters engaged in fire fighting operations and in
search and rescue are not placed at undue risk.
The general rule is that the taller the building
the more time should be allowed for occupants to escape. In the
UK, fire safety guidance to the Building Regulations usually requires
a combination of fire sprinklers and fire resistance of the structure.
In buildings over 30m in height, the building
must be sprinklered and the structural fire resistance must be
a minimum of 120 minutes. Longer periods of fire resistance may
be specified if it is considered necessary to protect the building
or its contents.
Although longer periods can be specified, we
believe that they are rarely used when considering life safety.
If the duration of fire protection of the structure is insufficient,
building collapse may occur whilst evacuation is taking place.
Regulatory guidelines for structural fire protection
are for life safety only. A building designed to these standards
will, in the event of a fire, probably result in total loss of
the building and its contents. As was demonstrated at the Twin
Towers in New York, collapse of a tall building can cause very
serious damage to neighbouring buildings.
Periods of fire resistance are notional figures
based on the way a fire will affect the contents of a building.
The test method was developed during the 1930's. It was based
on the effect of fire on cellulosic materials and a time-temperature
curve was developed. This is still used today, even though contents
may differ considerably from those of some 70 years ago. There
is now a much higher plastic and polymer content in buildings,
which will result in a different time-temperature curve from the
In spite of these differences, experience with
building materials and their behaviour in fire indicates that
structural fire resistance times specified in the guidance documents
still provide a good guide to how structures behave when fires
occur in modern buildings.
For buildings over 30m, regulatory guidance
also suggests a combination of 120 minutes structural fire protection
and sprinklers. However, for tall buildings eg office blocks and
particularly those where there is sleeping accommodation such
as hotels, domestic building (flats) etc, this level of fire protection
may be insufficient. We suggest that even for life safety purposes,
the structural fire protection should be at least 240 minutes.
Where buildings and contents need to be protected this level of
fire protection may need to be even be greater.
The combination of structural fire protection
and sprinklers is considered to be acceptable, but if the sprinkler
system proves to be defective in some way, eg whilst being maintained,
blocked valves or blocked sprinkler heads, inadequate water supply
etc, protection of the building will rely solely on the structural
measures. This, we believe, again demonstrates the need for longer
periods of structural fire protection for tall buildings than
currently suggested in guidance documents.
The integral structure of high-rise buildings
is generally of steel or steel reinforced concrete.
Steel loses its load bearing properties at about
550ºC, which is much lower than the melting point of steel
and much lower than temperatures reached in a fire. The temperature
at which load bearing properties of steel are lost is more important
than the melting point of steel.
This property of structural steel is well understood.
In order to prevent a temperature of 550ºC occurring, normal
practice is to protect the steelwork with an insulating material
that prevents the temperature of the steel from rising excessively
and remains in place under high temperatures experienced during
a fire. Typical materials manufactured by FSDG members are sprayed
compounds or board materials consisting of a reinforced inorganic
matrix, eg gypsum, cement etc. These products are robust materials
that, when suitably applied and fixed, can provide fire protection
for up to 120 minutes. Some products provide 240 or even 360 minutes.
2. STEEL REINFORCED
Steel reinforced concrete structures have not
been deemed to require additional structural fire protection because
the material is thought to provide the necessary level of fire
resistance in its own right. However, it is well known that reinforced
concrete will spall when subjected to fire conditions. The level
of spalling will depend on the type of concrete, the nature of
the aggregate, and the amount of moisture in the concrete. If
spalling is excessive, it will expose the steel reinforcement
and the structure may no longer retain the required level of fire
resistance. Premature collapse may result.
We recommend that more research be carried out
in this area before this design is used in tall buildings and
a firmer regulatory position established.
In normal circumstances, the fire protection
of steel and concrete is based on exposure to cellulosic fires
in accordance with the time-temperature profile expected from
the contents of the building.
However, during instances of irregular ignitionfor
example from a hydrocarbon source, such as petrol or aircraft
fuelfire exposure is significantly more severe. This is
reflected both in the rate of temperature rise and in the temperatures
reached. In certain cases, a high temperature torching jet-fire
can occur, when pressure achieved by the flame front is also much
higher than under conventional cellulosic fire conditions.
The fire protection industry is aware of these
more extreme conditions through experience of fire safety design
for onshore and offshore gas and oil platforms and petrochemical
works. In tall buildings, however, deployment of such techniques
would add significantly to costs and be well beyond normal risk
In high-rise districtsusually situated
in densely populated inner citiesbuilding-to-building fire
spread, when the external cladding of neighbouring tall buildings
become susceptible to ignition, should also be considered. External
cladding used on tall-buildings should not be of just Class 0
standard, but also non-combustible.
Fire protection in tall concrete or steel buildings
should be a key feature of the sustainable construction agenda
supported by the Government since 1997. After all, how sustainable
is any building if it is unable to withstand a fire situation?
For this reason we view with scepticism some
of the more avant-garde fire safety engineering solutions applied
in tall buildings. As mentioned above, this can mean concrete
or steel is inadequately fire protected, reducing the structures'
fire resistance. In a fire, this could destabilise the building,
making it vulnerable to collapse.
Environmental protection offers another reason
to install fire protection in tall buildings. Smoke and toxicity
emission during a fire is not only a major threat to life safety;
it can also be a serious pollutant. If poorly contained in the
fire's room of origin, emissions can cause damage to other areas
of the building and harm to the atmosphere.
Furthermore, many fire protection materialssuch
as fire resistant glass, mineral wool and plasterboardalso
provide heat insulation. While the impact of improved normal temperature
on a building's fire performance should not be neglected, it has
obvious advantages for energy efficiency and general environmental
sustainability. As part of its programme to combat climate change,
the European Commission has drafted proposals to improve the energy
efficiency of buildings across the EU.
However, the longer-term benefits of fire protecting
tall buildings have often been lost among policy-makers. Current
Building Regulations in England and Wales take insufficient regard
for property protection. In effect, once evacuated a building
can be deemed dispensable in a fire situation. The fire services
should be commended for their efforts to salvage propertyfire
fighters' lives are nonetheless put at extra risk.
The FSDG would therefore recommend to the Sub-committee
that tall buildings made from concrete and steel structures ensure
a properly and holistically engineered solution to fire safety.
This would give rise to environmentally friendly and more durable,
stable, safer tall buildings in the UK.
We would also urge Government to consider reinforcing
its sustainability programme by promoting protection of property