Structural Needs Help: Fundamental Burning Velocity

[preynolds]

I have been charged with designing a room containing styrene and associated pressure. I am currently trying to size the blast panel opening. I have the FM Global (insurance company) requirements for the design and they state that NFPA 68 may be more conservative. NFPA 68 does not list styrene (or by any other name) in their Annex D where they give the Fundamental Burning Velocity which is needed to determine the required vent opening.

Can anyone assist in helping me located the Fundamental Burning Velocity in cm/sec? I have the Chemical Engineers Handbook but so far I have found nothing.

Thanks in advance.
pat

 

[Flareman]

preynolds
Sorry to say you may not find it. Flame speeds are determined empirically. Good flame speed data is hard enough to come by for gases, let alone liquids which have to be warmed up so that they exceed a temperature at which the vapor pressure of the liquid exceeds the partial pressure of the flammable component in a flammable mixture with air.
For styrene,at ambient(?) conditions
LEL ~ 1.1% = 8.4 mm Hg
UEL ~ 6.1% = 46.4 mm Hg
Stoichiometric mixture ~ 2.06% = 15.7 mm Hg
Ambient Vapor pressure VP = 4.5 mm Hg
Flash Point is 88 degF (needs a nearby ignition source)
NBP = 294 degF
If you can find data for benzene (I think I read that it is about 20% faster than Propane, which is used in the NFPA std) it should be fairly close.
The NFPA assumes the maximum flame speed (which is at approx stoichiometric conditions). The curve is roughly Gaussian reaching zero at the LEL and UEL.
However, remember that combustion data is usually reported around 68 or 77 degF. Flame speeds increase with temperature and my guess is that you might have an elevated temp condition ?

Good luck
David