Like Jack and Capt stated, some wooden structure members can produce brownish smoke.
Depending on the structure you mention, there could be a number of other materials burning..such as, wood, paper, or cloth - all of which could produce grey-to brown smoke.
Cooking oil can produce brown smoke, whereas products such as Naphtha, Lacquer thinner and turpentine will produce black to brown colored smoke. Oxygen content plays a role in the color of smoke as well.
Even gunpowder can give off a yellow-brownish color, as does Nitrocellulose, sulfer and acids.
Good post you brought up. Color of smoke can tell a person lots, which of course is why as responders we always pay attention to what color the smoke is. It helps the investigators determine what or where to begin.
I have to wonder, what would the smoke look like when a POV with a blue light goes through it..aww forget it.. scratch that last comment lol
Oh, and by the way, another thing that will really get your mind going, is visiting your page! WTF??? talk about panic!! I could not find the exit, and was beginning to breathe rapidly.. Hard on the fn eyes too! lol just sayin..
Melvin, The structure of the house is burning(wood). You will see this alot when the structure is empty. In a house that as been moved out of. Smoke can always tell the story if we take time to watch it before we go into action.
From the pumper we would be saying "this is a goer... As with answers above, it could be many things.
Can depend on the structure itself, a house? The fire is probably into the wooden frame.
A factory? Probably contents - might be a furniture factory?
We'd be likely to be calling for more support as soon as we saw the smoke. If there was a lot of that heavy smoke, chances we'd be getting the message on turnout that there had been multiple calls, an indication that this could be a big one.
Want to extend you question? What if that heavy brown smoke was from a wildfire?
The color of smoke alone is not a proven science as to what is burning... I suggest viewing the actual program and learning about Volume, Velocity, Color and Density.
Fire Engineering offers David Dodson's Art of Reading Smoke-II; as a free webcast. Here is the link.