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Structures expert calls for extra sprinkler redundancy

SPRINKLER DESIGN in tall buildings will change significantly as a result of the fire damaged collapse of buildings around the World Trade Center, a leading structural engineering academic told NCE this week.

Dr John Knapton, who has advised twin towers' insurer St Paul's Syndicate in the wake of the disaster, said that sprinkler systems in tall buildings will have to be built with extra redundancy to cover for extreme events such as 11 September.

Following publication of the ASCE/FEMA report into 11 September, Knapton said that sprinkler systems in tall buildings should be designed with separate supply lines so that if one source dries up, another can be used.

Back up generators should also be provided to ensure the system doesn't break down, he added.

'If one pipe is ruptured, there should be an alternative path for the water. Buildings are structurally redundant so why not sprinklers as well, ' said Knapton.

The report says that sprinklers in fire damaged WTC7 on Vesey Street were only of 'light hazard design'. It collapsed just under seven hours after the second twin tower.

Only the core spaces on the fifth floor where the fire started were sprinkler protected.

Sprinklers on floor seven are thought to have run dry. Water on the site was limited because a 500mm water main on Vesey Street burst.

'It did not appear that there would be a sufficient quantity of water to control the growth and spread of the fires on multiple floors, ' says the report.

In the twin towers (WTC 1 and 2) sprinklers installed in 1990 worked but could not stop the fire spreading due to the rapid spread of aviation fuel.

In WTC 4, 5 and 6, the sprinklers 'did not control the fires'. Some sprinkler heads fused and failed to work.


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