a better more detailed report on the sulfur:
http://www.tms.org/pubs/journals/JOM...rman-0112.html
can be found here:
http://www.fema.gov/pdf/library/fema403_apc.pdf
As for a possible source for the sulfur all the UPS's (uninterruptible power supplies) we have at my work are powered by sulfuric acid, when they burn out, they boil and spread sulfuric acid all over the place in a cloud, this would be replicated if burned in a fire, if there were any UPS's in the area, it would be a likely source of the sulfur.
Here is a nice article about the reason behind the molten steel in the basement, a much clearer explanation than my last attempt.
http://www.geocities.com/debunking911/moltensteel.htm