Your browser is no longer supported

For the best possible experience using our website we recommend you upgrade to a newer version or another browser.

Your browser appears to have cookies disabled. For the best experience of this website, please enable cookies in your browser

We'll assume we have your consent to use cookies, for example so you won't need to log in each time you visit our site.
Learn more

Fuel in the debate

Letters

In your generally comprehensive coverage of the US ASCE/FEMA report on the World Trade Center collapses (NCE 8 May), you describe fires as 'intense'.

The report estimates that the planes were carrying 10,000 US gallons of fuel on impact - some 32,000kg. The fire energy of jet fuel is 45MJ/kg, so the total energy was 1.45TJ (terajoules).

However, the report concludes that 10% to 30% was consumed outside in initial fireballs, and that half the remainder drained away, leaving 40% - about 0.6 TJ - to burn.

The average fire load of an office floor is 8psf of wood, which over 30,000 sqft (2,800m 2) is 110,000kg. The fire energy of wood is 13MJ/kg, so the total fire load of one office floor is 1.4 TJ. The jet fuel therefore contributed only half a floor's worth of additional fire load.

Fire protection was 'a sprayapplied asbestos-free mineral fibre material', 19mm thick, later increased to 38mm around the entire impact zone in WTC1 but only floor 78 in the impact zone of WTC2.

The report, says impacts are 'believed to have dislodged fireproofing'. The lingering concern is the assumption that the behaviour was not dependent on the specific type of fire protection installed.

Stuart Alexander, group technical co-ordinator, WSP Group, Vantage House, Weir Road, London SW19 8UX

Have your say

You must sign in to make a comment

Please remember that the submission of any material is governed by our Terms and Conditions and by submitting material you confirm your agreement to these Terms and Conditions. Please note comments made online may also be published in the print edition of New Civil Engineer. Links may be included in your comments but HTML is not permitted.