How does fire expode a building?

Question

if a building had no windows and a bomb went off would it still be blowned. how does fire explode a building like that. does fire carry like 4oo mph winds with it. You see in the movies when the people be jumping when something explodes. where does the wind come from. Is the heat what causes things to move-stronger than wind. if you put a grenade in a metal bof 6 inch square thick, large, width and it was to detonate would it rip that box to piences

Answer 1

In addition to heat, an exposion typically produces more molecules than what was started with.  Consider something simple, like igniting ethanol vapor:

The ethanol reacts with oxygen to form carbon dioxide and water as follows:

1 molecule of ethanol reacts with 3 molecules of oxygen to form 2 molecules of carbon dioxide and 3 molecules of water.

You started with 4 molecules, and ended with 5.  Your products require 20% more volume than what you started with, that volume must go somewhere, otherwise pressure will build up.  If you are in a room, you will get a sudden rise in pressure because the extra gas is shoved into the same fixed volume.

For simplicity, suppose the starting pressure in the room is 1 atmosphere.  20% more molecules means about 20% more pressure.  If atmospheric pressure is 14 psi (pounds per square inch), the additional pressure will be 2.8 pounds per square inch.  If you have a 3 foot by 2 foot window, this is 864 square inches.  

When the ethanol "explodes", your window sees a sudden force of 864 X 2.8 = 2419 pounds of air pressure thrown at it, over one ton.  The window will blow out.

This simple example assumes the room is filled with ethanol vapor and just enough oxygen to burn it.  Actually, the calcualtions are slightly more complicated but I wanted to keep it simple for demonstration purposes.

Of course, all that additional gas would also be hotter than initially, so the pressure will actually be higher.  Also, many explosives are designed specifically to maximize the number of molecules produced after the combustion, thereby maximizing the pressure increase.

The primary destructive force behind an explosion is the pressure change resulting primarily from the increase in the number of molecules, compounded secondarily by the volume expansion due to heat.

Answer 2

When an explosive explodes, a chemical reaction takes a large part of it's material and converts it to a gas at a high temperature. The hot gas expands, and because it is very hot, it causes things to burst into flames.

Fire does not "carry 4oo mph winds with it". Fire is just something burning, combining with the oxygen of the air to create heat.

Heat does not "cause things to move". It's the explosion.

"if you put a grenade in a metal bof 6 inch square thick, large, width and it was to detonate would it rip that box to piences"

Yes

Answer 3

In case you havent noticed, when air is heated it expands. During a fire in a pressurized building, the fire of course heats the surrounding air. Since fire needs oxygen to stay burning, the fire itself is not as large since the air it needs has already been used. The pressure may cause glass windows to burst from the inside out and the rush of oxygen coming into the building from the make-shift vent has now fueled the fire with rich oxygen from outside and causes it to rage up again. Thats called feeding the fire and it happens so quickly, it looks like an explosion. As far as your "grenade" try it and let me know what happens.