THERMAL BALANCE?

[Paul Grimwood]

Recent posts here and letters in a magazine have prompted the question - What do you, as firefighters, understand by the term 'Thermal Balance'? I have my own views on this but it appears there is confusion out there as to what this term actually relates to. Any ideas?

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[SBrooks]

Well, you usually hear it in terms of "upsetting the" in relation to indirect attacks. I take this to actually refer to thermal layering.

BTW when are you gonna come over here and offer a "public" class?

[FyredUp]

Hi Paul,

Well you have seen my definitions before and I will post them here agian. These were what was taught to me way back about a million years ago in basic fire training class.

Thermal balance is when the temperature at the lowest point (floor) in an area is nearly the same as at the highest point (ceiling) in an area.

Thermal imbalance is when the majority of the heat, smoke and fire gasses have accumulated at the highest point (ceiling) in an area and the lowest point (floor) is substantially cooler.

Take these for what they are worth.

Take care and stay safe,

FyredUp

I would like to have you come teach a class on this side of the pond too. A lot easier to relate to what you can actually see, hear and feel.

[FD111]

I will echo what SBrooks said in that you usually hear it in the terms of "upsetting the thermal balance". I have always learned about it when discussing "Thermal Layering".

[benson911]

I believe in this basic law of physics: hot gases rise and cool gases drop. If a room is in "balance" with this law, the hotter air is at the ceiling and the cooler air is at the floor.

Thus, "thermal balance" means the state to which the atmosphere will return if left to act naturally. A room is out of balance if it is otherwise.

It's not nice to fool with Mother Nature.

[Paul Grimwood]

Try this link for up-to-date definitions of THERMAL BALANCE.............
http://www.firetactics.com/THERMAL%20BALANCE.htm

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[SBrooks]

I wouldn't say that a balanced situation is one that will reoccur if left alone...if i balance a pencil on the edge of a table, and it is knocked off, it is highly unlikely to return to the original state.

Since thermal energy is always moving unless there is absolute equalility amongst all temperatures, there can be no "balance" until the end of the universe.

[Hosekey21]

When you talk about a pencil being balanced on a table, it is the pencil that is balanced, not the pencil and table grouped together that is balanced. Therefore the pencil will return to a balanced state when it lands on a floor or something else after being knocked off.


[This message has been edited by Hosekey21 (edited 03-08-2001).]

[benson911]

I'll follow the pencil analogy -

The pencil lying horizontal is in balance, its natural balance. The pencil set on end is only temporarily in balance - it'll fall over with the slightest breeze.

The room with higher heat at the ceiling than the floor is in natural balance (pencil on its side) and will remain that way due to the natural law that heat rises. If I introduce something to upset that balance (set the pencil on its end) then it will correct itself.

I don't like your analogy, though. A pencil set on end is still in balance unless an outside force acts upon the pencil - Newton described this physical law as an object at rest will remain at rest unless acted upon by another force. Any container with an atmosphere within it will have its warmer molecules at the top and cooler molecules at the bottom due to the natural law that heat rises.

A container with the hotter molecules at the bottom will (unless acted upon by an outside agency) correct itself to fit the natural law. The cooler molecules will sink and the hotter molecules will rise.

Thus, my belief that a room with its atmosphere in "thermal balance" is in a naturally occuring state. A room "out of balance" has been upset by outside forces to put the hot stuff on the bottom.

But, that's my opinion and it obviously does not meet with some texts. I guess all that matters is the student understands what the instructor means by thermal balance in the context in which they are learning.

[SBrooks]

yeah, yeah, sumthin like that.

I believe the word we're looking for is equilibrium. The world seeks it's lowest point of equilibrium. Pencil on table not happy until it hits the floor, pencil on end not happy until it falls over. Cold gasses at ceiling not happy till they fall. Warm gasses not happy until they're cool. Fuel not happy until it's spent. Compressed gasses not happy until they're released. Etc. etc. etc.

[benson911]

I agree with SBrooks - we all try to find happiness in everything we do. A happy fire is a good fire.

[LadderCapp]

Wow guys, this can be summed up I think without a masters degree in physics. The heat inside the room of involvement is higher closer to the ceiling. When you hit the room with a fog stream for too long it pushes the heat to the floor. The nozzleman doesn't feel it as much as the poor schmuck about 4 feet back. But a quick attack direct at the seat with a straight stream, or a smooth bore even keeps the heat at the ceiling. And since I as the company officer will be the poor schmuck about 4 feet behind him, I prefer my guys to hit it quick and get on with business. Somewhat simplistic I know, but hey the bottom line is that the fire room is hot and we gotta cool it down.

[SBrooks]

Hey Cap

While I agree with your statement, I've gotta bust your chops...

As the "laddercapn" shouldn't you be doing something besides backing the lineman up?

[LadderCapp]

lol,, chop busting is part of the service. And yes if there is something that needs done I'm all in for doing it. I'd prefer to be doing something more than just hanging around at the tail end of the attack doing the supervising thing. But my dept. is fairly stringent on the company staying together and if hanging out and backing up my attack crew is the task of the moment so be it.

[LadderCapp]

Also take into account that my ladder is a 100' quint. So whether we are 1st in or 4th in has a drastic effect on what task I will become assigned to.

[Paul Grimwood]

Any more views o this subject? I appreciate your knowledge and viewpoints and accept that there may be varied definitions?

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[mfgentili]

I agree with most everyone else here. To me Thermal Balance is the state at which a burning compartment reaches naturally ie. hot at the ceiling and cooler at the floor.

If left alone, and lacking an outlet for heat release, I think the entire space could conceivably reach the same temperature and still be in Thermal Balance as long as it occured naturally. That would in effect be the Thermal Balance for that space at that stage of the burning curve.

I think of Thermal Imbalance, or upsetting the Thermal Balance as when we as firefighters introduce air or water into the burning room causing a homogenous mixture of the layered temperatures. This can be caused by opening windows or doors, operating hose streams, or in some cases just by our own movements. Next chance you get to go into a flashover simulator, put your hand up into the lowering smoke layer and move it around in a circular motion. You will see an upsetting of the Thermal Balance just by the movement of your hand.