I can tell you from having been in a building that had a major fire, the speed with which smoke and fire spreads is hard to imagine. Within 30 seconds of the alarm, halls where filled with choking smoke.

I managed to exit without too much difficulty, but even with covering my face with my shirt, I was still coughing and black gunk coming out my nose for the rest of the day. Others needed oxygen support even after being in the smoke for minutes at most.

If you’re ever in a house or building when an alarm goes off, don’t think you have time to ponder the situation... just move outside to safety immediately.

Edit: Found some photos from that day.

http://archive.boston.com/news/local/massachusetts/gallery/1...