The Pecular Behavior of Fire

[Rhondazvous]

Fire gives off light but does not act like light.

If you light a torch and hold it aloft the fire will shoot upward. But if you hold the torch horizontally, the fire will still shoot upward. Whereas if you hold source of light, such as a flash light, horizontally the light will continue horizontally.

No matter how far fire spreads it maintains its triangular shape, sometimes producing several triangles with one angel pointing upwards, unless it encounters a downward facing surface such as a ceiling. Then the fire spreads along the surface and that surface becomes it's base. It resumes its triangular shape when it eats through the surface to the air above.

Is there a scientific theory of fire that accounts for this behavior?

[ApeNotKillApe]

Air pressure. Heat makes flames less dense than air, hot gas rises, air pressure forces flames up.

[Rhondazvous]

Air pressure. Heat makes flames less dense than air, hot gas rises, air pressure forces flames up.

Excellent explanation and easy to understand. What accounts for the triangular shape?

[ApeNotKillApe]

Cold gas is more dense, gravity pulls it down, oxygen feeds the flames and becomes heated, pushing it upward. What you're seeing is the distribution of heat as air is heated, pressured and forced upward through a bottleneck of pressure, sort of like squeezing on a thing of toothpaste.

[Whateverist]

Air pressure. Heat makes flames less dense than air, hot gas rises, air pressure forces flames up.

Excellent explanation and easy to understand. What accounts for the triangular shape?

That would be the hand of God.  

[Rhondazvous]

Cold gas is more dense, gravity pulls it down, oxygen feeds the flames and becomes heated, pushing it upward. What you're seeing is the distribution of heat as air is heated, pressured and forced upward through a bottleneck of pressure, sort of like squeezing on a thing of toothpaste.

I see. So fire dances and crackles because the rising heat is fighting against the falling cold air.

[vorlon13]

Ever wonder why the plume coming out of the back end of a rocket gets so big the higher the rocket goes?

Less air pressure up there, so the exhaust fans out more.

[ApeNotKillApe]

Cold gas is more dense, gravity pulls it down, oxygen feeds the flames and becomes heated, pushing it upward. What you're seeing is the distribution of heat as air is heated, pressured and forced upward through a bottleneck of pressure, sort of like squeezing on a thing of toothpaste.

I see. So fire dances and crackles because the rising heat is fighting against the falling cold air.

The details are naturally more complex, but that's my understanding as a layman.
Crackling is the result of a build-up of pressure in pockets of moisture in the burning material (notably wood) as it vaporizes into steam, expands and bursts out.

[Rhondazvous]

Ever wonder why the plume coming out of the back end of a rocket gets so big the higher the rocket goes?

Less air pressure up there, so the exhaust fans out more.

Then the first few seconds after take off are the most dangerous because of backup. I'm sure NASA has come up with a way to minimize that danger.

[Rhondazvous]

I see. So fire dances and crackles because the rising heat is fighting against the falling cold air.

The details are naturally more complex, but that's my understanding as a layman.
Crackling is the result of a build-up of pressure in pockets of moisture in the burning material (notably wood) as it vaporizes into steam, expands and bursts out.

Devil in the details. Guess that would take a deeper understanding of exactly what fire is. e=mc2 kind of stuff.