As skyscrapers proliferate at home and abroad, what can be done to mitigate the special fire risks they might pose? Simon Adams throws light on this, with a close look at firefighter policy
WHILE THE UK is not renowned for its abundance of skyscrapers, since the mid-20th century the number of high-rise apartment buildings and office blocks has grown significantly. In recent years our major cities have seen a boom in the number of skyscrapers proposed and approved for construction, and with new architectural masterpieces such as the Shard in London, we can now lay claim to owning the tallest building in Europe.
There are almost 60 buildings in the UK standing at least 100m tall and if all of the under-construction and approved buildings are actually built, the figure is expected to double in the next few years. The shortage of land and space in our biggest cities has prompted tall building applications, with the most common uses varying from major hotel chains and office blocks, to residential apartments and hospitals.
The height of a structure has a significant impact on the safety of the building and its occupants, particularly as regards fire safety and firefighting. Generally, there are no guidelines as to what defines a tall building, although any structures below 30m have less stringent regulations for fire safety engineering. In the fire industry, a high-rise building is considered to be one containing floors at such a height, position or design that external firefighting and rescue operations may not be feasible or practicable.
In many ways, designing a fire system for a tall building is no different than it is for any other building. Every system is designed specifically for each individual space and, regardless of the size of the structure, it is always subject to the risk assessment. Designers are bound by the risk assessment carried out at the time of the build, which identifies the fire hazards and the people at risk. The ‘responsible person’ must carry out and regularly review a fire risk assessment of every premises. The intention is to evaluate, remove or reduce the risks, and record the findings, then prepare an emergency plan and provide training, as well as review and update the fire risk assessment regularly.
Currently, in terms of fire safety engineering, there are no differences in standards or requirements for buildings more than 30 metres high. However, in practice, individual tall buildings are analysed in relation to their own design, to develop a rationale for fire engineering. This is discussed with the fire authorities, district surveyors and other approving bodies. The onus is on the fire engineer to demonstrate that the proposed fire solutions meet or better the requirements of the intent of the regulations.
For tall buildings, one common design element is the inclusion of firefighting shafts to protect access within the building for the fire and rescue service. Firefighting lifts are currently used for heights greater than 18m. The possibility for the use of fire-rated lifts for evacuation of tall buildings is also under consideration, in light of developments in technology that can now provide computerised control of lifts in emergency mode.
The most important part of a building’s risk assessment is that it determines the category of design of the fire system, setting out the required level of protection. For all building sizes, the risk assessment would highlight the hazard, risks and control measures for any operational incidents involving high-rise buildings. The design of the system would be the same as that of a normal build, with the same detection principles, and detector and design philosophy – based on the risk assessment. The key differences with tall buildings, compared with other configurations, are the greater vertical distances for escape and the subsequent increased firefighting difficulties.
Aside from the primary purpose of providing an adequate means to prevent a fire, there are several important considerations for the fire detection and alarm (FDA) system that must be reflected in the fire strategy.
In multi-storey buildings, one of the most vital elements of an FDA system is its capability to provide early warning and automatic detection. The most suitable device is dependent on its location in the building and the type of environment it is operating in. For example, many tall buildings contain boiler rooms that need a specific type of sensor with the ability to perform correctly despite the high temperature. The ideal sensor would have to detect minimal heat rises
to be able to assess whether a fire has started.
Multi-sensor devices have programmable sensitivity states that can be configured to address specific known risks, which in turn would significantly reduce potential false alarms. An example is the Gent S-Quad detector, which in plant rooms uses patented dual angle optical scatter to detect very dark smoke particles rather than clear steam, which is already present in this type of room. In a building with a multitude of floors and occupants, it would ensure the best form of false alarm protection, as the different sensor states would ignore the steam travel and only activate if there was a real threat from smoke or fire.
Early warning and detection is about knowing the environment in which the device and fire alarm system is being installed, and tailoring each individual device to the assigned area. To ensure the best false alarm protection and prevent unwanted signals being triggered, it is vital to combine the elements within the sensor – and the system itself – with the specific environment in question.
Means of escape
Protected escape routes from tall buildings must be managed effectively and the evacuation procedures have to take into account the potential need to
vacate a building full of thousands of people in a short space of time. In tall structures, phased evacuation is the most common procedure to manage the occupants safely and avoid potential crush situations in lifts and stairwells.
During a phased evacuation, the first alert would be sent to the floor that it is in the fire condition, telling the residents to leave the building. Then, an alert message or tone would be sent to the floors immediately above and below that floor, to notify them of an incident and to await further instruction. One or two floors directly above and below the incident would be evacuated first, followed by those people occupying the highest floors of the property, and then by people on the lower floors of the building. The risk assessment will determine the estimated time for total evacuation of the building and the amount of provision for fire protection required will vary, depending on the length of time.
Voice alarm (VA) systems are frequently used to assist these phased evacuations. A live audio feed can be put into the FDA system, and then programmed to use precise messaging appropriate for that building. To prevent panic, the VA systems have the ability to play numerous coded messages through the speakers. For example, in a building occupied by young children, nursery rhymes can be played via the speakers to give a coded message to staff, so they can calmly carry out the evacuation procedure without causing unnecessary distress to the children.
In high-rise properties, there has to be provision for smoke control to prevent fire spread throughout the building. Generally, this is in the form of smoke dampers and smoke vents. Staircase pressurisation and smoke control systems are provided in fire-rated air shafts. The smoke dampers are activated by the FDA system and are used in air conditioning and ventilation ducts to control the flow of smoke.
Many FDA systems can be programmed in zones to automatically close the dampers in a specific zone and limit the smoke travel within the rest of the building. Large open atrium areas are common features of tall buildings. For smoke control in buildings of this design, auto window openers can be linked to the fire system so that, in the event of a fire, the high windows will automatically open to release the smoke from the building.
Limiting fire growth
Aside from controlling the spread of smoke, the growth rate of a fire can also be controlled using several methods. Extinguishing systems can be considered, to flood high quantities of gas in specialist areas such as computer server rooms and offices containing very high value equipment. Sprinkler protection is also provided throughout tall buildings as an automatic means of firefighting. The sprinklers are interfaced in line with a mechanical pump to spray water, mist and vapour through nozzles and prevent the growth of a fire.
Determined by the material of the building, which acts as a firebreak, the degree of fire containment is usually measured in either 30 or 60 minutes. For example, between floors of a building there is a 60-minute barrier, which means the material can burn for this period before its does any damage. In breaks on floors, it is generally a 30-minute fire break.
Fire service facilities
Given the significant challenge to firefighters presented by the sheer scale of these buildings, many of the larger structures have introduced measures such as a permanent fire service presence based on site. Other European countries, such as France, have developed additional security measures to address firefighting issues by locating crews permanently in the property. Although this is not yet a mandatory requirement in the UK, as the skyline changes, more firefighting teams are being based in offices. Many of the taller buildings – for example some larger hospitals – have facility teams fully trained in fire safety which can tackle minor incidents such as bin fires, while the major incidents are still handled by the external fire authorities.
The fire industry is well aware of the additional threats associated with dealing with incidents in larger buildings. Those involved in fire prevention in high rise buildings, from occupants to landlords, architects to builders, or the fire service itself, are working together to meet all of the requirements of the risk assessment and provide the best protection for the building and its occupants. Firefighting in high-rise buildings needn’t be a tall order as, with a stringent risk assessment and the right equipment in place, we can ensure that the UK’s rising skyline stays safe and protected.
Simon Adams is business manager at Gent for the South West and Wales.