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C H A P T E R
Fire safety and airport design
Airport terminals are hazardous buildings in terms of fire.
Their deep plans and enclosed volumes mean that smoke extraction is a priority; the concessionary areas (shops, restaurants and bars) pose high fire risk; the number of people milling around mean that should a fire break out, many will inevitably be affected; and there are often long escape distances. However, terminals are also well- managed places with orderly routes and disciplined people, and because they are mainly open buildings, passengers can readily move away from the seat of a fire. Also, airports have their own on-site fire brigades and well-drilled staff, and should a fire break out the response time is quicker than in conventional situations.
Designing for fire safety consists of:
• determining the relative risk in different areas of the terminal
• establishing likely smoke patterns and spread of fire
• making assumptions about levels of occupancy
• determining the extent of fire containment by compartmentation and the fire loads involved
• using the ‘islands’ approach to smoke extraction and sprinkler systems
• determining the position of fire alarm and smoke detection systems
• making assumptions about fire brigade and airport staff response times
• determining the likely structural response of the building in the event of a fire.
The traditional method of rigid compartmentation has given way to the ‘islands of risk approach’, whereby much greater openness is permitted, and smoke extraction is encouraged by interior height. Large internal volumes divided by a combination of fire compartments and smoke extraction and sprinkler systems above the high-risk areas are replacing the earlier emphasis upon compartmentation alone.1
Most recent airport buildings have abandoned rigid fire compartmentation, because it tends to obstruct movement
essential for the smooth passage of people and baggage from landside to airside. Not only do fire partitions and self-closing doors physically interrupt movement, they also obscure the legibility of routes at a perceptual level. Today terminals tend to be designed on the principle of openness, with islands of greater fire risk (such as shops, bars, seating areas and check- in desks) protected by sprinklers (some using partial foam deluge systems) and smoke extraction hoods. Elsewhere interior volume and building height are encouraged, because smoke can be naturally extracted by windows in the roof, and as smoke not flame is the killer in most fires, large volumes mean that the density and hence the toxicity of smoke is reduced.
Identifying islands of potential hazard and spacing them sufficiently apart to prevent fire spread from one to another is the approach at Kansai.2At each high-risk island, containment of the fire by smoke extraction and sprinkler systems is preferred to an approach whereby the whole of the terminal is treated equally. Having identified the fire-risk islands, each is evaluated according to level of hazard, and the choice of materials, sprinkler system and method of smoke extraction modified accordingly. The fire at Frankfurt Airport in 1996
spread because no such island containment policy applied:
at Frankfurt, as at most traditional terminals, there was an overall sprinkler and smoke extraction system, which did not discriminate in terms of level of risk.
Because smoke and heat rise in the event of a fire, it is possible to modify the ceiling profile to draw toxic chemicals out of the building. Again, the openness and interior transparency at Kansai meant that even in a building of 15 million m3it was possible to design for fire safety without physical subdivision of the terminal. The design approach, which encourages natural extraction, also supports passenger orientation in the event of a fire. As long as the exits, routes and stairs can be readily comprehended, large open volumes underpin, not inhibit, smoke evacuation in the event of a fire. Identifying risk islands and forming containment around them leads to a new approach to fire engineering. It means, for instance, that minimum distances need to be established between islands; that voids between floors are needed to allow smoke to rise to the roof; and that subsequent changes in the distribution and density of shops, bars and check-in desks need corresponding changes to sprinkler and smoke hood systems.
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14.1 Openness and height have replaced gloomy first generation airports. Terminal 2, Charles de Gaulle Airport. Architect: Paul Andreu.
Many fires are started deliberately, and to avoid oppor- tunities most airport authorities have introduced a policy of avoiding concealment sites. Hence modern terminals tend not to have litter bins, left luggage areas or unlocked cupboards.
Preventing an arsonist from starting a fire or a terrorist from planting a bomb, by designing for openness and visibility of all public areas, tends to be the practice today. Where concealment sites are inevitable for other reasons (as in toilet cubicles) their design must seek in the choice of materials the containment of a fire or blast.
As most modern terminals are constructed of structural steelwork, this needs to be protected from fire. The usual standard is for the frame of a terminal to have a fire rating of 11/2hours in public areas and 1 hour in offices. The steelwork needs to be encased (by, for instance, glass-reinforced cement) to a height above floor level of 4 or 5m; the remaining exposed structural steelwork must be painted with intu- mescent paint; and concealed structure must be lined with dry boarding. While smoke is the main killer for humans, it is flames
that do the most damage to the structure of airports. Where risk of flame spread is high (as in baggage areas) there need to be masonry fire walls separating these areas from public concourses.
Lighting
Much has already been said about light as part of the essential architectural experience of terminals, but light is also an important technical consideration. The artificial lighting of terminals is normally the chief source of energy use (exceeding that of heating or cooling), and the means of lighting, the lamp sources used etc. have great impact upon comfort, safety and general ambience. The trend towards greater natural lighting in terminals is a means of saving energy, of reducing the build- up of heat from artificial sources, and of helping with passenger orientation. But the balance in energy use between natural and artificial lighting is complex, and much depends upon local conditions. The heat loss through windows has to be made up Lighting
14.2 Visibility, spatial permeability and daylight are a feature of today’s terminals. Cologne/Bonn Airport, Germany. Architects:
Murphy/Jahn.
14.3 Satellite Pier, Terminal 2, Charles de Gaulle Airport. Architect: Paul Andreu.
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by energy released from other sources, and this generally entails fossil fuel. For any given terminal there is an ‘optimum glass area which depends on the climate and orientation of glass’.3Given that light levels in terminals are normally similar to that in offices (especially where tickets have to be read, and where security is important), designers need to calculate carefully the relationship between window area, orientation and subsequent fabric heat loss.
The working light level in terminals is normally 200 lux, but this standard varies according to the degree of security or tranquillity of space. Such a figure suggests an upper daylight factor of about 4 per cent, which invalidates the totally glazed facade at a stroke. Where large areas of wall or roof glazing are used (as at Stansted or Kansai) it is angled, shaded, screened and treated in a fashion to reduce daylight (and particularly sunlight) penetration. At Stansted, for example, the 11m rooflights over the concourse sit above a perforated metal shade, which reduces the light transmission by 50 per cent.4
Few terminals are designed without natural lighting and electric lighting being considered from an architectural point of view in tandem. It is important to maintain a similar pattern
of lighting by day and by night so that passenger perceptions of route and volume do not vary. This means that some electric light is used in the day even if not justified by external light levels. A common pattern is to design for a natural lighting daylight factor in concourses of 1 or 2 per cent in combination with electric lighting design of about 500 lux.5The result is that while electric lighting overwhelms natural lighting, there is still a sense of ‘daylight’. Where daylight alone is used to light concourses, on overcast days the lack of sparkle can make for dull interiors.
The close juxtaposition of natural and artificial sources of light means that the designer can feel confident that the architectural experience remains much the same throughout 24 hours. Again, referring to Stansted, the system uses 400 watt lamps clustered at each structural tree shining upwards so that the light is reflected off the roof adjacent to the skylight.6 The result is that both natural light through the roof and artificial light are concentrated immediately above the structural tree, giving them visual emphasis within the terminal. Light therefore draws attention to the structural concept, which – being uniformly applied – helps passengers to understand the logic 14.4 The external envelope of the terminal has to balance light penetration against solar gain, and the designer needs to alter window design according to orientation. Bangkok Airport, Thailand. Architects: Murphy/Jahn.
and organization of the building. A similar philosophy prevails at Kansai Airport, where the rooflit canyon (or central street) has artificial light sources concentrated along its length. Because of the crucial question of passenger orientation, it is vital that architectural design and lighting design (both natural and artificial means) share the same approach.
Similar principles apply to wall lighting. A vertical window admits only about 40 per cent of the daylight of a horizontal rooflight, but with a low sun glare can be a problem through windows. Sunlight penetration through vertical windows brings the adjoining interior spaces alive, but direct sunlight can lead to discomfort, especially for people sitting or working directly in its rays. As a result, wall glazing needs to be screened (either externally or internally), or the angle of glass tilted (as at Zurich Airport) or curved (as at Kansai). As a rule, glare tends to be a problem associated with wall not roof glazing.
A combination of external screening, roof overhangs and surface treatment of the glass can deal effectively with glare while also allowing good levels of daylight penetration. Except for the deepest planned terminals, natural light from wall and
roof glazing can be adequate for daylight hours. There is the need, however, to increase general light levels at key points in the building: ticket check-in, baggage areas, passport control and around shops and restaurants. Here the pattern tends to be to intensify light levels by artificial not natural means. So while general concourse areas are mainly naturally lit (and in some cases ventilated) there are pools of brighter electric light and specific task lighting (as at check-in desks). These more brightly lit areas, often located near the centre of the building, lead to high levels of energy use and consequent heat build- up. Lighting and heating design then need to be considered together, with building management systems employed that recycle the heat from lights in cold weather.
Many modern terminals are designed as passive solar buildings: the transparency helps with energy conservation, security of the building itself, and general appearance. But excessive glazing, added to lack of thermal capacity in the fabric, can lead to great heat loss in the winter and heat gain in the summer. Largely glazed terminals, though they save on artificial lighting, lead inevitably to partial or complete air-conditioning (often requiring the use of ozone-damaging CFCs).
Heating
Heating, lighting, the thermal capacity of the terminal, occupancy levels and the transparency of the envelope are related factors. Most terminals of any size rely upon air-conditioning for part or all of the year, and part or all of the building. Most systems use circulating air as the means of heat or cooling distribution. The profile of the building aids the circulation of air: for instance, the undulating and curvaceous forms of Kansai, Oslo and Charles de Gaulle are a direct response to air circulation. Typically, air-conditioning circulates cooled air in the summer and warmed air in the winter. Air is normally blown into the concourse spaces horizontally and rises or falls depending upon its temperature. The shape of the space is an important factor in the degree of penetration of the blown air, and the patterns of air movement established.
It is not architectural fashion but air-conditioning that determines the curved undulating roof shapes of many recent terminals. The natural curve of a jet of blown air at a set Heating
14.5 Architect’s sketches for the lighting design at Bangkok Airport, Thailand. Architects: Murphy/Jahn.
temperature and velocity produces its own distinctive profile.
Combining this with structural and spatial geometry leads inevitably to the distinctive new generation of terminals seen today.
Because air rises or falls according to temperature, the angle of discharge of air-conditioning nozzles needs to be capable of adjustment. At Kansai, nozzles positioned immediately beneath the roof distribute air at different angles
according to specific need, with air drawn back in via planting boxes on the floor. The angle of nozzles can be adjusted electronically according to the season.
Most airports have macro and micro systems for heating.
The former provide background heat (or cooled air) to the whole terminal, the latter to specific areas such as the arrivals walkway. In good building services design the micro installations often use recycled heat from the macro system.
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14.6 The Futurist imagery of modern airports is based upon the expression of architectural structure, movement and walls of light.
Bangkok Airport, Thailand. Architects: Murphy/Jahn.
Fabric canopies as at Kansai and Denver, are sometimes used to deflect recirculating air or provide solar screening.7
Because terminals are lofty structures it is usually possible to exploit the ‘stack effect’ to encourage natural ventilation and to establish circulating air currents. Also, height means that the level of occupation (the lower 3m zone) can have different characteristics from those of the remainder of the interior volume. Hence it is only really necessary to heat or cool the levels that passengers use; the other spaces can have quite different temperature characteristics. With large volumes it is also possible to exploit the principle of night-time cooling whereby air at say 16°C is circulated through the building at a sufficient rate to cool the fabric, which then maintains an acceptable temperature during the day. Heating systems that rely upon circulating air allow this to happen, and if the equipment is integrated into the structure then it does so with coherence and elegance.8
Most terminals rely upon heat extraction systems to recover the heat from extirpated air or water in order to increase the temperature of the fresh air. At Stansted a central refrigeration plant extracts heat from the chilled water to keep it cool and then discharges the heat into a water circulating system at around 40–50°C.9 This heat is then used for the main air-handling system. During most of the year the heating load
can be met by heat extraction, but in particularly cold weather (below 5°C) boilers provide back-up.
Safety and security
The trend in terminal design towards greater transparency and openness is partly the result of increasing concern over airport security. Large glazed malls allow security staff to monitor what is happening both inside and outside the terminal, and the natural light that flows through glazed rather than solid walls improves the effectiveness of CCTV. High levels of natural light give greater definition to the images on security screens and, in particular, allow facial features to be discerned. Designing for maximum transparency is the norm, because it allows police and airport security staff to see everything that is going on. In fact, one in three of all BAA staff work in security in one form or another.
As designs for airports are being generated, the layouts are subjected to risk analysis by the airport authority and police.
Overcoming security risks by good design is a growing aspect of design monitoring prior to construction. While the trend towards greater openness and transparency in terminals is driven partly by passenger wayfinding needs, the avoidance of obstruction or walls behind which terrorists can hide (or place Safety and security
14.7 The profile of roofs is often determined by the flow of air released under pressure at low level and extracted at high level. Oslo Airport, Norway. Architects: Aviaplan AS.
bombs) is of equal importance. Of the six elements that form BAA’s Mission Statement, the first is ‘safety and security’, thereby confirming the highest priority given to this aspect of airport management.
There are three distinct approaches to effective security design: surveillance, space syntax and territoriality.
Surveillance
The effective surveillance of the interior of terminals and key exterior points is crucial in the creation of a safe and secure environment. The airport lounges, shopping areas, toilets and entrance points are particularly at risk, and require surveillance directly by security staff and indirectly via CCTV cameras.
Places where cars are allowed to drop off or pick up passengers adjacent to terminals pose special risks, and here management policy towards parking has to be especially vigilant.
Surveillance is most effective in terminals that are spacious and open. Well-placed cameras and patrolling police can monitor behaviour more effectively in such areas. Where physical enclosure is needed (such as around shops, bars and toilets) there needs to be extra surveillance provision, which is often provided by additional cameras placed in strategic locations. Crime prevention and airport security are mutually beneficial concerns, and cameras or security staff can detect either form of anti-social behaviour.
Surveillance is normally undertaken by uniformed security staff, police and plain-clothes detectives, and via conspicuous or hidden cameras. The range of personal and visual monitoring of terminal spaces is aimed at combating many types of crime, from pocket-picking to drug couriers, and from terrorists to baggage thieves. Airport design has a part to play in crime prevention by providing areas, routes and entrances that can be readily overlooked.
Space syntax
This is a measure of the number of people using an area of terminal space at any particular time. Safe places are those that are occupied at an optimum level: under-occupation of space poses a potential threat, as does over-occupation. At
levels of over one person per square metre there are dangers, and at under one person per 20m2there are also risks. High levels of human density make visual surveillance difficult, and the bumping and colliding of people and trolleys pose a danger from petty thieves as well as from risks of physical injury. Low levels of space occupation, particularly in corridors or smaller spaces, expose passengers to attack, armed robbery or mugging.
Space syntax is not an easy balance to achieve. In large spaces, such as airport lounges, low levels of occupation are restful, but the same density of occupation in more confined spaces (perhaps when there are only two people per length of corridor) can pose a threat. There are age and gender issues involved as well. Female users of terminals feel safer in buildings that are relatively heavily used, and fear unused spaces, especially late at night (perhaps after a delayed flight).
Ageing passengers too fear lack of human contact, especially where their reduced mobility may place them behind other passengers.
It is by no means easy to design terminals at optimum levels of space syntax. The erratic pattern of use of airports means that terminal spaces change during the day from being heavily crowded to being sparsely populated. What architects can do, Technical standards
14.8 The level of human usage helps make the airport feel safe but over-occupied spaces are inherently dangerous.