Fire engineering for modern high rises involves consideration of psychology and human behaviour just as much as it does physical building design.
The deployment of effective methods for the evacuation of high-rise buildings is an issue of increasing concern for both the developers and denizens of Australia’s urban environments – particularly given projected population gains and attendant increases in the density and building heights of city centres.
The importance of evacuation measures for high rise buildings was drawn into the spotlight by the fire which broke out at an apartment complex in Melbourne’s inner-city Docklands district last year, zipping vertically up the building to the 21st storey in a matter of minutes.
According to Dr. Weng Poh, National President of the Society of Fire Safety, Engineers Australia, the problem of high-rise evacuation is one which the developers of the country’s building codes are still struggling to address.
“We build buildings taller and taller, and I don’t know how many people are sitting down and asking themselves, how do we evacuate these tall buildings – it’s a problem,” said Weng. “If you turn back the clock, I don’t think any of us imagined a building which would be a hundred storeys high or something like that. For the BCA, 25 metres is considered be a tall building.
“Now we have many buildings that are many times taller, and the codes are still trying to catch up with technology.”
Weng notes that the challenge of evacuation from high-rise buildings is an intrinsic part of creating large-scale structures.
“If we take a step back and ask how do we get people into tall buildings, say the top level - you have to use lifts – there’s no way of walking up there because the distance is too great," he said. “The question then becomes how do you bring people out? If you say we need to walk all the way down, it’s a long, long way to walk. I’m not sure everybody can actually make it – I definitely can’t.
“In that sense the codes – not just in Australia but around the world, haven’t caught up with and solved this issue.”
Weng points to a number of potential solutions for shoring up fire safety in high rise buildings, including evacuation lifts, refuge floors and protected places.
“We can use lifts for evacuation, although it can be quite tricky, because you can’t use normal lifts - you have to design them specifically,” he said. “You have to look at it from an engineering viewpoint, not as a code-prescribed method.”
“For a brand new building, if you were to use lifts for evacuation, you have to specifically design to protect the lift, make sure the lift is designed specifically for evacuation, by way of controls, by way of protection, and so on. And then you have to pay substantially more for these measures.”
A chief problem with the use lifts for evacuation purposes is the prevailing wisdom that stairs are the only safe means of exiting in the case of fire.
“For decades people have been trained not to use lifts in the event of fire, so it’s conditioned in your mind not to use them at all in emergencies,” Weng said. “So now suddenly my building is designed for using the lift for evacuation. People might not even want to do that, because they’re not aware of it, or unsure. This is probably the hardest thing to overcome – it will take time to educate people.”
Another option at hand is the refuge floor – a protected zone where building occupants can find safe harbour in the case of emergency.
“Some tall buildings overseas already require the use of refuge floors,” Weng said. “This means high rise buildings come equipped with protected refuge floors every 20 to 30 storeys, to which people can be evacuated for temporary refuge before deciding later how to evacuate them fully.”
Protected places similarly involves obviating the need for full evacuation by shoring up the fire resistance of a building.
“The other way we have is protected places – not evacuating as opposed evacuating the building,” Weng said. “For example there’s a fire on the 20th floor, you’re on the 100th floor – do you need to evacuate, or can you just stay there and be safe on that floor because of protections that are in place?”
According to Weng, protected places could be an effective means of safeguarding building occupants during fires given the fact existing building codes partially contribute to their creation in residential high-rises.
“In some ways [protected places] have already been in building code requirements for a long, long time,” he said. “Taking apartments as an example – each apartment is what we call a fire cell, because the surrounding wall is fire-resistant, and each floor is separate.
“In some sense it’s quite safe to stay in an apartment in the event of fire, and this is by default the result of the way they’re required to be built. So then it comes down to the question of, in the event of fire, is it better to stay within your apartment, or to evacuate?”
While a variety of practical solutions exist for improving fire safety in high-rise buildings, Weng notes that all of them entail more than just changes to the physical infrastructure of buildings, but amendments to the mentality and behaviour of occupants as well.
In the case of lifts, it involves educating people to use the machines for evacuation purposes during fire – running completely against the grain of multiple decades of modern safety training in buildings.
When it comes to refuge floors and protected places, it means training occupants to remain within buildings when fire occurs in other parts of the building structure, which would probably strike most people as counter-intuitive.
“The effectiveness of these measures depends so much on education,” said Weng.“It’s a lot of psychology and things like that – more so than just engineering and design.
“This is why fire engineering has to be looked at from a human behaviour and engineering perspective simultaneously – and not just with an engineering mindset."