Positive Pressure... neighbours' house?

[J.Beck]

I understand it just fine. I might not be quite done with my MS in fire protection engineering but I think I' ve got that particular bit down pat. :P

What I'm trying to understand how you are applying it to detached exposures and you're being annoyingly evasive about responding to direct questions. Unless the detached exposure is very close (effectively attached) and/or the smoke and fire gas velocities exiting the fire building are very high, pressurizing the detached exposure is doing a lot of work for very little benefit because the primary means of heat transfer is going to be radiation -- not smoke and flame directly entering unprotected openings.

"Annoyingly evasive"

Interesting.

Ok, let me ask you a few things; how is pressurizing an un-attached structure a lot of work? What follows radiant heat exposure?

[DeputyMarshal]

Don't believe that I am using that specific information in context?

Suffice it to say I'm not sure you're applying it accurately.

You seem to be fairly interested in the subject. Or at least interested enough to try and prove it wrong..

I don't particularly need to "prove it wrong" but, since it flies in the face of typical fire behavior, I'm asking you to back up your assertion which you seem very sure of.

Don't rely on me 100% for your PPA/PPV knowledge. Buy some books. Do a google search, etc.

I'm certianly not relying on you for anything except to back up your assertion. I have a couple of thousand dollars worth of fire technology and engineering texts on the shelf now. You'll excuse me if I don't go out and buy a book just to hunt down a citation that you won't (can't?) supply.

All of my information is coming directly from NIST, UL, simple science principles, numerous live burns and multiple text books/trade journals.

Cool. Citation, please. Pretty much everything NIST has ever done is published online so that would be a good place to start and it wouldn't require going out and buying any books.

EDIT: please don't twist what I said...what I stated was, "for every decrease of 18 degrees the speed of the chemical reaction leading to combustibility decreases 50%" not, "combustibility doubles with every 18 degrees".

Totally different.

I'm sorry if you think paraphrasing is "twisting your words" but the net mathematical result is the same.

BTW, that isn't what you said anyway:

For every 18 degrees dropped in temperature, combustibility is decreased by 50%.

[DeputyMarshal]

Ok, let me ask you a few things; how is pressurizing an un-attached structure a lot of work?

A minimum of one crew that could be used elsewhere to better effect; ventilation equipment that could be used elsewhere to better effect. Like I wrote before, if you have the luxury of excess manpower to perform low gain tactics, knock yourself out.

What follows radiant heat exposure?

Typically, ignition of the exposure's exterior unless it's protected. If you fail to protect it to the point of fire infiltration (IOW, if you're doing a poor job of exposure protection already), it'll eventually breach the exposure's envelope. At that point, pressurization is helpful. Of course, if you allow it to progress to that point, it isn't an exposure at all but a second fire building.

[J.Beck]

[QUOTE=DeputyMarshal;1234647]
Cool. Citation, please. Pretty much everything NIST has ever done is published online so that would be a good place to start and it wouldn't require going out and buying any books.
QUOTE]

Being a grad student, you certainly know about different research principles.Buying the book is only one way to do research.

Here is a great place to start.

http://positivepressureattack.com/im...veThinking.pdf
http://fire.nist.gov/bfrlpubs/fire05/PDF/f05018.pdf
http://fire.nist.gov/bfrlpubs/fire07/PDF/f07011.pdf
http://cfbt-us.com/wordpress/?p=541
http://firechief.com/tactics/firefig...reinforcement/

A simple google search will reveal numerous other links that deal specifically with pressure gradients..no need to spend thousands of more dollars on books.

[J.Beck]

A minimum of one crew that could be used elsewhere to better effect; ventilation equipment that could be used elsewhere to better effect. Like I wrote before, if you have the luxury of excess manpower to perform low gain tactics, knock yourself out.



Typically, ignition of the exposure's exterior unless it's protected. If you fail to protect it to the point of fire infiltration (IOW, if you're doing a poor job of exposure protection already), it'll eventually breach the exposure's envelope. At that point, pressurization is helpful. Of course, if you allow it to progress to that point, it isn't an exposure at all but a second fire building.

One crew to set up a fan?
A single firefighter could accomplish the same task in a few minutes.

Not allowing the fire to breach the exposures envelope (interior) is the exact reason you pressurize the exposure. Of course, I will state it again, pressurizing the exposure should be done in conjunction with handline exposure protection.

This exact thing happend yesterday. The second due crew was assigned exposure protection - the officer ensured the exposure was sealed up and threw a fan to the front door, his crew pulled a handline and put it in between the exposure and the fire. Pretty simple and it worked great.

[J.Beck]

I'm sorry if you think paraphrasing is "twisting your words" but the net mathematical result is the same.

The net mathmatical result is not the same.

How are "doubling" and "50%" of a variable number the same?

[DeputyMarshal]

Here is a great place to start.

I'm just looking for a source for your assertion that "For every 18 degrees dropped in temperature, combustibility is decreased by 50%." And somewhere that CPS is applied to sturctural firefighting -- I'm not looking to do a thesis on the subject.

Can you supply citations for those specific assertions or not? Yes, or no.

[DeputyMarshal]

One crew to set up a fan?
A single firefighter could accomplish the same task in a few minutes.

Once I break up a crew to get one firefighter, the crew is out of service anyway so why not send them both? Besides, two are more efficient than one.

Not allowing the fire to breach the exposures envelope (interior) is the exact reason you pressurize the exposure.

That's not going to be much help unless the detached exposure is pretty damned close to the fire building. But then, I've mentioned that already.

Of course, I will state it again, pressurizing the exposure should be done in conjunction with handline exposure protection.

Pretty simple and it worked great.

If you beat two sticks together it will keep the tigers away. I did it just now and there's not a tiger anywhere in sight. Pretty simle and it worked great.

[Rescue101]

Once I break up a crew to get one firefighter, the crew is out of service anyway so why not send them both? Besides, two are more efficient than one.



That's not going to be much help unless the detached exposure is pretty damned close to the fire building. But then, I've mentioned that already.

Of course, I will state it again, pressurizing the exposure should be done in conjunction with handline exposure protection.



If you beat two sticks together it will keep the tigers away. I did it just now and there's not a tiger anywhere in sight. Pretty simle and it worked great.

No it didn't. Those two damn Tigers hopped a bus and are now at MY house. Thanks a BUNCH DM,hehe T.C.

[J.Beck]

Once I break up a crew to get one firefighter, the crew is out of service anyway so why not send them both? Besides, two are more efficient than one.

In my neck of the woods two people is not a crew. Two people is two people. A crew or company would consist of 4-6 firefighters.

Assigning a single firefightera safe exterior task that is not labor intensive is a no brainer for what is gained.

[J.Beck]

I'm just looking for a source for your assertion that "For every 18 degrees dropped in temperature, combustibility is decreased by 50%." And somewhere that CPS is applied to sturctural firefighting -- I'm not looking to do a thesis on the subject.

Can you supply citations for those specific assertions or not? Yes, or no.

Looking for a source?

I gave you the source...and no, I don't have their book in front of me to quote it verbatim.

[DeputyMarshal]

The net mathmatical result is not the same.

How are "doubling" and "50%" of a variable number the same?

"Doubling on a constant increase" and "halving on the same constant decrease" are just two ways to describe the same relationship: If the relationship is such that it "doubles" going up, then it can also be said that it "halves" (x50%) coming down.

[DeputyMarshal]

No it didn't. Those two damn Tigers hopped a bus and are now at MY house. Thanks a BUNCH DM,hehe T.C.

No problem. Get two sticks... :P

[J.Beck]

http://www.firedistrict7.com/section...r/Positive.pdf

"For every 18 ° F the temperature of an ordinary combustible is decreased, the off-gassing or pyrolitic decomposition of the material decreases 50 percent. Although not exactly correct, one could infer that the ability of ordinary combustibles to burn is decreased 50 percent for every 18 ° F
decrease in temperature."

[DeputyMarshal]

In my neck of the woods two people is not a crew. Two people is two people. A crew or company would consist of 4-6 firefighters.

There's that surplus of manpower I referred to before... On those days when we have the luxury of a 4 to 6 man company, the smallest crew size that company can typically be split up into is still a minimum of two. ("Crew" is an ICS/NIMS term if you're not familiar with it in this usage.)

Since you imply that your smallest crew size is 4 to 6, aren't you committing even more manpower to this questionable tactic than I was already giving credit for?

Assigning a single firefightera safe exterior task that is not labor intensive is a no brainer for what is gained.

Setting up PPV isn't necessarily an entirely exterior task but we'll let that go for now.

[ChiefKN]

Once I break up a crew to get one firefighter, the crew is out of service anyway so why not send them both? Besides, two are more efficient than one.

Do they always hold hands?

[DeputyMarshal]

Looking for a source?

I gave you the source...and no, I don't have their book in front of me to quote it verbatim.

In other words, no, you can't provide a citation. Thank you for finally answering the question.

[DeputyMarshal]

Although not exactly correct, one could infer that the ability of ordinary combustibles to burn is decreased 50 percent for every 18 ° F decrease in temperature."[/I]

Thank you for pointing out in your incomplete citation that this is an unsupported inference that is explicitly "not exactly correct."

I wonder why you left off the qualifier on the reply?

The reason for this is the rapid decrease in temperature within the fire building...

So the discussion isn't really directly applicable to a detached exposure is it?

[DeputyMarshal]

Do they always hold hands?

We try not to notice.

[J.Beck]

Thank you for pointing out in your incomplete citation that this is an unsupported inference that is explicitly "not exactly correct."

I wonder why you left off the qualifier on the reply?



So the discussion isn't really directly applicable to a detached exposure is it?

Incomplete citation?

The qualifier was not intentionally left out. In fact, the first time I seen that specific statement was when I quoted it. The fact still remains unchanged, regardless of how backhanded you choose to be.

The discussion was NEVER about using the two concepts (exposure protection/heat reduction) together. I even acknowledge this much earlier in the discussion. You are choosing to lump them both together.