FIRE SAFETY DEVELOPMENT GROUP

  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.

INTRODUCTION

  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.

FIRE PROTECTION OF TALL BUILDINGS

  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.

STRUCTURAL FIRE PROTECTION

  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 1930s original.

  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.

1.  STEEL

  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 CONCRETE

  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.

IRREGULAR IGNITION

  However, during instances of irregular ignition—for example from a hydrocarbon source, such as petrol or aircraft fuel—fire 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 assessment requirements.

  In high-rise districts—usually situated in densely populated inner cities—building-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.

SUSTAINABILITY OF TALL BUILDINGS

  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 materials—such as fire resistant glass, mineral wool and plasterboard—also 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 property—fire fighters' lives are nonetheless put at extra risk.

CONCLUSION

  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 against fire.