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FIRE SERVICE AND GENERAL FIRE SAFETY TOPICS => Technical Advice => Topic started by: Ashley Wood on January 02, 2006, 07:37:24 PM

Title: Formula for calculating fire loads
Post by: Ashley Wood on January 02, 2006, 07:37:24 PM

Can any one advise me as to how to calculate fire size i.e car fire in tunnel, HGV in tunnel, platics, etc etc?

Thanks

Title: Formula for calculating fire loads
Post by: Peter Wilkinson on January 06, 2006, 02:03:10 PM

Yes, why not have a look at PD7974-1?  Section 5.7 onwards should help along with Annex A which gives heat release data for lots of different materials and items.

Title: Formula for calculating fire loads
Post by: Ashley Wood on January 06, 2006, 04:49:24 PM

Thanks for the help.

Happy New Year to you.

Ashley

Title: Formula for calculating fire loads
Post by: Gary Howe on January 16, 2006, 01:17:05 PM

Fire load can be calculated as follows:-

Weight of material in Kg (mass) X Calorific value of the material - Answer in Kj

For example 1 tonne of propane @ a calorific value of 47.3 x 10 to the power of 3 Kj/Kg

= 1000 x 47.3 x 10 to the power of 3 = 47300 Kj

If you want to relate this to wood equivalent the formula is:-

mass x calorific value divided by the calorific value of wood, for example (with the calculation above):

1000 x 47.3 x 10 to the power of 3 divided by the C of wood (17.6 x 10 to the power of 3)

 = 47300000 divided by 17600

 = 2.7 tonnes (wood equivalent)

Regards


Gary

Title: Formula for calculating fire loads
Post by: Ashley Wood on January 16, 2006, 01:42:57 PM

Thanks for your help Gary.

Best regards

Ashley

Title: Formula for calculating fire loads
Post by: Fishy on January 17, 2006, 09:40:07 AM

Gary:

Point of clarity; your calc may give fire load in wood equivalent, but it won't result in a fire size (in MW), which is what the original post was requesting.   Obviously, if the material(s) in question release the energy quickly, then you can get a big fire, even if the fire load is reasonably low (it just doesn't last as long)!  This may be important if the figures are being used to develop smoke control or suppression systems.

Fishy

Title: Formula for calculating fire loads
Post by: wee brian on January 17, 2006, 01:13:56 PM

Well said Fishy.

You need to have an idea of how quickly the fire will grow and how much of the fire load is likely to be consumed.

Its often better to use results from tests on real items. These are done in freely ventilated considtions so tend to go a bit quicker than would occur in a confined space.