Fires In Corners Of Rooms

[Tadees]

At College of Knowledge, I recall being told that fires in corners of rooms spread quicker than fires in the centre of rooms, but no reason, as far as I can remember, was given.  What are the reasons for this?

[Golden]

Lack of entrainment of cool air all around the fire plume results in higher temperatures in the upper layers of the room/plume heating other items in the room more readily than a fire in the centre of the room - depends on room height and some other factors but you would achieve a faster flashover.

[SamFIRT]

Also; the solid walls can reflect, (or absorb, conduct and re-radiate), the heat (IR EM energy). In the corner of a room this acts similarly to a parabolic mirror effect, shining the IR EM out into the room. Also; the hot smoky gasses (HSG) are drawn towards the pair of conjoined walls (the corner) by the Coanda effect and therefore run up the corner, creating a faster upward flow. Also the ceiling has only a 45 90 degree arc ( normally) to allow the HSG to spread out and therefore they are forced out over the ceiling as if from a venturi or jet. If the fire is in the middle of the room the HSG plume can spread out over 360 deg and therefore dissipate the heat more effectively.

[Tadees]

Also; the solid walls can reflect, (or absorb, conduct and re-radiate), the heat (IR EM energy). In the corner of a room this acts similarly to a parabolic mirror effect, shining the IR EM out into the room. Also; the hot smoky gasses (HSG) are drawn towards the pair of conjoined walls (the corner) by the Coanda effect and therefore run up the corner, creating a faster upward flow. Also the ceiling has only a 45 degree arc ( normally) to allow the HSG to spread out and therefore they are forced out over the ceiling as if from a venturi or jet. If the fire is in the middle of the room the HSG plume can spread out over 360 deg and therefore dissipate the heat more effectively.

Hmmm, something just flew over my head.

[John Webb]

A fire in the middle of the room has fresh air all around it ie for 360degrees, so although the fire burns well, the rising plume easily entrains more air. This dilutes the hot gases to slow the rate of temperature rise in the plume. On hitting the ceiling, the spreading plume entrains more air, further limiting the rate at which the temperature rises. Heat is lost to the ceiling over a large area, until the room walls are reached.

But in the corner of a room, air can only get into the plume from a quarter of the circumference of the fire (90deg, which is what SamFIRT meant by his 45deg?). Likewise as it spreads across the ceiling, it is advancing on a more limited circumference which means less air to entrain into it and a smaller ceiling area to lose heat to. So the plume will be hotter and therefore warm things up more quickly. Being at a higher temperature than the unconfined centre of room plume, it is more buoyant and it will spread at a faster rate.

[SamFIRT]

Yes ... 90 deg.....   ... Thanks John... corrected my original post.

[Fishy]

...plus if the wall linings are combustible they'll more quickly contribute to the heat release...

[Tadees]

Thanks guys.  Much appreciated.

[William 29]

More surface area of fire involved more quickly. i.e. fire in the corner two walls and ceiling involved. Fire in center of room takes time to reach ceiling depending on height etc, etc.