Ho Chi Minh City in Vietnam has few tall apartment blocks, partly because of the poor fire record of older tall buildings. Buildings over 100m tall are not covered in current Vietnamese fire codes.
So when WSP Fire Engineering was asked to provide support to the 34 storey Vina Conex Tower project, destined to be the tallest building in Vietnam, the choice of code was critical.
WSP Fire Engineering technical director Simon Lay says the Vietnamese authorities are willing to adopt foreign codes for specific projects. 'They're quite comfortable with US fire codes, ' he says. 'But the problem with these is that some underlying assumptions about available fire fighting resources aren't really appropriate for Vietnam'.
A review and cost analysis comparing US, UK, Hong Kong and local codes was the first step. The concrete framed tower is predominantly residential, with a retail podium and a restaurant/ bar on the top floor. 'US codes rely very heavily on sprinklers in this type of structure, ' Lay reports. 'But we had doubts about long term maintenance and the availability of spare parts.
'And Hong Kong codes would have required simultaneous evacuation of all residents and the provision of refuge floors in the tower, as well as compartmentalisation.' By contrast, the UK approach is to compartmentalise the residential floors, and expect residents to sit tight until the fire brigade arrives. Fire loads in residential buildings are generally not high enough to promote vertical spread of flame externally, and 'box to box' spread horizontally is very slow.
'The biggest problem with evacuating residential buildings is timing, ' Lay says. 'When do you give the alarm- And will everybody take notice- Experience suggests that most people only leave their apartments after 15 or 20 minutes - by which time the fire brigade has arrived, there are hoses everywhere, and smoke and combustion products adding to the confusion.' This approach proved difficult for the Vietnamese authorities to accept. The final decision was to design to Hong Kong codes, but use fire engineering techniques to produce 'a building that would be inherently safe for its entire lifetime.' This meant no fire alarm, no refuge floors but the extensive use of compartmentalisation, as in the Hong Kong codes.
WSP has also recommended that sprinklers could be omitted, thanks to rationalisation of the floor plans.
'Generally, sprinklers in residential areas aren't cost effective, ' Lay says. 'But they can allow designers to open up apartment layouts, and protect large open areas.
'So far the authorities haven't ruled on our proposals to omit sprinklers on this project.' For the large 80m by 40m basement car park, sprinklers would seem to be the natural choice. But reservations on long term serviceability remain. WSP has instead opted for powerful, robust 'jet fans' of the type normally found in road tunnels.
These move very large quantities of air over burning vehicles, cooling everything down and blowing smoke away from the source of the fire to make fire fighting easier.
Lay says it is relatively easy to get the idea of performance based fire engineering solutions accepted by the authorities in countries unfamiliar with the concept - provided the right person in the local hierarchy is won over. The approach adopted for the Vina Conex Tower should also be popular with potential residents, he believes.
'People actually prefer the idea of protected apartments to the possibility of lots of false alarms and unnecessary evacuations. But this isn't an approach that should be taken lightly.
'Anyone can build a block wall with a two hour fire resistance. But getting all the details right is another matter. On this project, engineered partitions are the answer, forming an effective fire barrier.'