Positive Pressure... neighbours' house?

[DeputyMarshal]

As I said, I'm a skeptic of PPV in many cases, and this seems like a an extrapolation of a only somewhat proven tactic. I know it works when it works, but so do water curtains. Both fail miserably, when they fail too.

FWIW, PPV used properly is a very effective tactic. The problem is, I've seen a lot of totally botched attempts at PPV. "Water curtains," OTOH, don't work at all.

[DeputyMarshal]

That building is standing today because of 40 or so sprinkler heads outside on the adjoining wall. They were pressurized by an engine, and acted as a sort of wall mounted water curtain.

Direct cooling by wetting an exposure works just fine; a traditional "water curtain" between the fire and the exposure does not.

[slackjawedyokel]

Our water curtain appliance is designed to tilt so it can flow across the surface.

[slackjawedyokel]

And back to the original question - it worked well in our situation , the only thing I would have done differently ,would to be have someone stationed at the fan to kill it if there was a wind shift or an inversion of some sort. This was an extermely smokey fire and took a long time to self vent. (multiple roofs /ceilings ) we also had gone completely defensive when we initated the ppv on the exposure and had two lines and a portion of the drop ceiling down to monitor the entire wall. (no vents in the flat roof)The fan was in the C/D corner of the exposure building (one story)and the vent was the front door on the A side of the exposure.

[Rescue101]

I think a lot of FF's lose track of two things about PPV. One: It's a TOOL. Two: That TOOL should have an OPERATOR with it and it DOES have a THROTTLE which DOES NOT necessarily have to be set at full throttle. I LIKE PPV's, have used them on various building constructions. Used with DISCRETION they can speed up your work and make your life EASIER, Used IMPROPERLY: Hello PARKINGLOT! T.C.

[DeputyMarshal]

I LIKE PPV's

Minor nit-pick: PPV is a tactic, not a tool. This tactic is usually implemented using a fan (tool) -- either gasoline powered or electric -- but can occasionally even be accomplished by taking advantage of a convenient wind.

I do agree with your overall assessment.

[Rescue101]

Minor nit-pick: PPV is a tactic, not a tool. This tactic is usually implemented using a fan (tool) -- either gasoline powered or electric -- but can occasionally even be accomplished by taking advantage of a convenient wind.

I do agree with your overall assessment.

I agree with your assessment. For the purposes of the THREAD however,I DON'T think the OP was thinking Mother Nature PPV. T.C.

[6Duron1]

Sounds like it helped slack

[J.Beck]

Pressurizing an exposure is VERY effective.

I have used it and had success on the following exposures; strip malls, a dwelling w/ attached garage and adjacent high rise floors.

The higher the interior pressure, the more effective it will keep fire out!

[DeputyMarshal]

Pressurizing an exposure is VERY effective.

You might want to reread the initial post. The OP appears to be talking about detached exposures.

[J.Beck]

You might want to reread the initial post. The OP appears to be talking about detached exposures.

I probably did misunderstand the OP, although, the point remains the same - pressurizing an exposure, attached or not, is VERY effective.

[DeputyMarshal]

I probably did misunderstand the OP, although, the point remains the same - pressurizing an exposure, attached or not, is VERY effective.

For a detached exposure, effective at doing what?

[J.Beck]

For a detached exposure, effective at doing what?

Eliminating fire spread to the given exposure.

[DeputyMarshal]

Eliminating fire spread to the given exposure.

How do you propose that pressurizing a detached exposure will prevent fire spread given that fires typically spread to detached exposures either by radiant heat or direct flame contact; neither of which is effected by pressurization?

[J.Beck]

How do you propose that pressurizing a detached exposure will prevent fire spread given that fires typically spread to detached exposures either by radiant heat or direct flame contact; neither of which is effected by pressurization?

Pressurization has everything to do with keeping out direct flame contact and radiant heat.

As fire spreads it seeks to go to a neutral or negative pressure (outside air, non-pressurized buildings, etc). Fire will not spread where there is a positive pressure, thus the reason for pressurizing exposures.

[DeputyMarshal]

Pressurization has everything to do with keeping out direct flame contact and radiant heat.

Pressurization has zero effect on both of those modes.

As fire spreads it seeks to go to a neutral or negative pressure (outside air, non-pressurized buildings, etc). Fire will not spread where there is a positive pressure, thus the reason for pressurizing exposures.

Pressurizng a detached exposure does nothing to prevent either radiant heat or direct flame contact from igniting its exterior. If you want to keep a detached exposure from igniting, keeping heat/fire off of its exposed surfaces is typically going to be a far superior strategy to pressurizing it.

[J.Beck]

Pressurization has zero effect on both of those modes.
Pressurizng a detached exposure does nothing to prevent either radiant heat or direct flame contact from igniting its exterior. If you want to keep a detached exposure from igniting, keeping heat/fire off of its exposed surfaces is typically going to be a far superior strategy to pressurizing it.

Of course traditional exposure protection via. charged handlines must by utilized for proper exterior exposure protection. But, to protect the entire(interior/exterior) structure, pressurization must also be utlized.

[DeputyMarshal]

Of course traditional exposure protection via. charged handlines must by utilized for proper exterior exposure protection. But, to protect the entire(interior/exterior) structure, pressurization must also be utlized.

If you protect the exterior the interior isn't a primary exposure.

Of course, if you have the luxury of excess manpower standing around with nothing better to do, go for it...

[RFDACM02]

Fire will not spread where there is a positive pressure, thus the reason for pressurizing exposures.

Good lord, do you understand basic fire behavior or heat transfer? How does PP affect radiant heat transfer or conductive transfer?

It's amazing that more of us haven't burned down blocks ignoring the use of positive pressure on exposures. Where I live, if the positive pressure can protect a house, they probably would rather have it burn then pay the heating bill.

[J.Beck]

If you protect the exterior the interior isn't a primary exposure.

Of course, if you have the luxury of excess manpower standing around with nothing better to do, go for it...

Capiche.