An interview with Stephen Logan, Aurecon Technical Director Buildings
There is enormous variability in approval processes from country to country, therefore no one leading design trend. However, the adoption of performance-based fire safety has increased with wider understanding of the subject in industry.
Fire safety is quite a new engineering discipline, only really emerging in the 1980s. The skill base is small and relatively few skilled practitioners exist. Opportunities exist to evolve current practice, technologies and commitment to facilitate a functional and safe built environment.
So if anything, the trend overall is the increasing use of scientific method in fire safety, rather than simple application of prescriptive codes.
You have to think about how the existing prescriptive codes have evolved. In a way, they arise as a result of “codifying by catastrophe”. Historical adverse outcomes, such as loss of life in fire are responded to (quite reasonably) by more onerous building regulations. But these regulations, built up over time, can become illogical for some types of buildings.
The English “Green Guide” (the Guide to Safety at Sports Grounds) is a classic example of “codifying by catastrophe” as it was produced following the horrific Bradford and Hillsborough stadium disasters in the UK, in the 1980s.
Many modern building codes (including the Australian National Construction Code) recognise the limitations of a purely prescriptive approach and instead simply require a series of Performance Requirements be met. This is where the expression “Performance Based” fire engineering comes from. But because it would not be cost effective or sensible to adopt a different performance based solution for every routine project there are also prescriptive clauses, in effect a recipe book of measures that are “deemed to satisfy” the performance requirements.
The language of this is revealing. You can say that if you follow the prescriptive clauses, you are assuming that this gives you a safe building, because the codes are deemed to satisfy the performance codes. By comparison, a performance-based approach demonstrates fire safety.
Some people seem to think that adopting a performance based approach is about cutting cost, or getting away with things. In fact, it is about demonstrated, rather than assumed safety.
Apart from proving that the building design is safe, fire safety engineering offers:
As I said, fire engineering has really only been around in any significant way since the 1980s. Part of the reason is that fire engineering is heavily reliant on computing power and software tools. Another part of the reason is the gradual worldwide trend away from building approval by local government and towards more uniform, performance based codes. This is a good thing because local authorities sometimes don’t have the skills to deal with large complex projects.
As I said, fire engineering has really only been around in any significant way since the 1980s. Part of the reason is that fire engineering is heavily reliant on computing power and software tools. Another part of the reason is the gradual worldwide trend away from building approval by local government and towards more uniform, performance based codes. This is a good thing because local authorities sometimes don’t have the skills to deal with large complex projects.
The main issue is the number of people and their behaviour. The whole fire safety strategy in a stadium should be considered from a behavioural perspective. But there are also other significant issues:
Population in stadiums are high. If escape paths are calculated in the normal way, the perimeter of the stadium can be dominated by escape stairs and concourse widths can become excessive. A better way is to simulate egress flows using computational modelling and optimise the escape paths.
But the big issue is thinking about the behaviour of the occupants and designing from there.
Actually panic is not a problem. In general people don’t panic. In fact, in a few situations a bit of panic would have improved things – like in the Bradford Stadium fire when people remained in their seats waiting for the game to restart, when they should have been evacuating.
In a fire emergency, most people go through four behavioural steps before they even begin to evacuate.
Disbelief – patrons don’t believe it is happening. If they hear an alarm, they will tend to assume it is a false alarm.
Commitment – patrons typically finish what they are doing. If they are buying a snack, they will finish doing that before they investigate further. In the Kings Cross Underground fire in the 1980s people were observed stepping over hoses deployed from fire trucks to get to escalators to go underground. They were committed to getting their train home. In numerous tests in the retail environment, patrons observing actual smoke will take their goods to the check-out, rather than move to a fire escape.
Affiliation – patrons assemble in friends/family groups — won’t evacuate until then. This is a huge issue in stadiums. When a patron is away from his seat is convinced that there is a fire emergency, they will not evacuate — they will return to their seats to re-unite with family members first.
Seek authority figures – once they have formed their social and family groups they will look for authority figures to tell them what to do. But they must be perceived as having authority. A teenage usher employed on the day of the event may not be perceived as an authority figure. Where do people in a sports stadium look if they don’t know what is going on? The scoreboard!
Etihad Stadium, Melbourne, Australia. For the multi-purpose sporting facility designed to seat up to 74,000, Etihad Stadium project, we based the fire safety design around the following key questions:
For example, on an event day, the venue might have 52,000 patrons and 400 casual staff including about 50 back of house, 40-50 media, 150 catering and 150 people concerned with ticketing and ushering. The number of permanent venue staff could be as few as 20.
Therefore, it is safest and most efficient if the event manager controls a fire situation with as few people as possible.
Fire and smoke simulation tools such as computational fluid dynamics (CFD) help predict how big a fire might become, how much smoke is generated and where the smoke and heat might go.
Pedestrian movement simulation helps design evacuation routes in an effective way. Sometimes this is counter-intuitive. At RAC Arena, Australia we reduced the width of the corridors out of the bowl, in order to improve the egress time. This might sound counter-intuitive, but reducing the rate that patrons entered the concourses improved the flow on the concourses, so the overall egress time was better. The image on the right is from that work.
General people movement will be more sophisticated, the simulations will get more sophisticated with greater realism with people moving as a group together. I anticipate more architecturally impressive designs that will present big fire engineering challenges.
About Stephen
Stephen is one of Aurecon’s building design engineers with extensive experience in fire safety. He leads our Building Sciences team globally and has 25 years’ experience gained in Perth, Adelaide, Brisbane, Melbourne and London. You can contact Stephen at stephen.logan@aurecongroup.com
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