"As Engine 15 turned up Liberty street Captain John Kahl could see light smoke from the top floor of the Hurst Building. Captain Kahl did not think he had much of a fire so he went to check the automatic alarm box. The box indicated that there was fire in the basement, so Captain Kahl had his crew force entry threw a glass door on the German street side and entered the building with a 3/4 inch chemical line and 2 1/2 hand line. As the crew was standing on the stairs to the basement they could see the fire rolling across the ceiling towards the elevator shaft. It was not long after Captain Kahl entered the building when a smoke explosion occurred in the elevator shaft. The explosion was powerful enough to blow off the roof , break several windows and also throw large embers across the street into the broken windows of several buildings. All the firefighters escaped with out injury"
Originally Posted by Gravy
What you have just read describeds what firemen call a smoke explosion at a fire in Boston. This phenomenon occurs when a fire creates a pocket of hot explosive gas in an enclosed area. The gas comes from material in the area of the fire that is heated to the point of giving off gas, but the area is not hot enough for spontaneous combustion to occure. All it takes is a spark or the inrush of oxygen rich air to make the gas ignite. Its similar to a backdraft but in a backdraft the gas has space to expand and burn, in a smoke explosion the enclosed space make the effect more explosive in nature.