Babrauskas, Dr. Vytenis. Glass Breakage in Fires. The Fire Place. Feb-Mar
1998. p 15-17.
Abstract: Fire seeks oxygen and will sometimes break out windows
and other glass to find it. The damage done in a fire can be greatly affected
by whether or not the windows break out. The glass must not just crack;
it must fall or break out for sufficient oxygen to aid the fireís
development. Because fire ventilation openings need to be known for fire
models to be used, if and when glass breaks out has become of particular
There are at least two distinct types of thermal exposure glass is subjected
to in a fire: exposure from an inside fire, causing immersion heating from
one side and a possible temperature gradient; and exposure from an outside
fire, where heating is by radiation, temperatures more uniform, and a cooling
flow of air along the glass is possible.
The article briefly reviews studies of glass cracking in fires. The author
puts the data together from several studies and determines that at a room
gas temperature of around 450 degrees Celsius, the probability is 1/6 for
thin, single pane glass to break out. Even at high heats, exterior fires
did not cause glass to fall out. The author concludes that it is difficult
to predict when glass will break out. Factors that influence when glass
will break out include window size, frame type, glass thickness, glass defects,
presence and degree of overpressure, and vertical temperature gradient.