Positive Pressure Ventilation

Replies to This Discussion

Permalink Reply by Art Zern on December 3, 2008 at 11:05pm

Brian and Jim,

How does this sound for a conversation starter?

Permalink Reply by Brian Arnold on December 3, 2008 at 11:40pm

Art and Jim,

Sounds good to me. I guess I'll get it started by throwing out a few things on Single Family Dwellings first.........

In Okc, the majority of our structure fires are in ranch style dwellings. Some two story but most are single story. Usually the truck officer has the call on what type of ventilation is utilized and we open alot of roofs. When my knuckle dragging brethren (like Scotty K) are contemplating whether to use horizontal, vertical or PPV we utilize the AEIOU acronym.
DO NOT USE PPV with the following conditions-
A- Attic fire
E- Exhaust opening too small
I- Imminent rescue (if path of smoke and heat cannot be 100% controlled)
O- Over pressurized occupancy (due to increased interior temperatures from the fire)
U- Unable to locate the fire

This pretty much limits our truckies to using PPV on single room and contents type fires and for post knockdown. Even then we don't put the fan in place until the attack lines are stretched, charged and ready to advance on the fire. As an engine officer, the truck officer can be my best friend and make my job easy; or he can make mine and my crews life miserable and cause a fight on the front lawn. To me, a smart well trained and seasoned truck officer is worth his weight in GOLD! As much as I like to tease them, the truck officer's have to know as much about fire behavior and fluid dynamics; if not more, than the hose draggers......and that kills me to have to admit that sometimes. All the more important to work together and communicate with each other.

The little tidbits that are taught about PPV from various firefighting text are only ice breaker conversations in class and don't fully explain what the hidden dangers of what PPV or PPA can be. How many people have actually read the NIST studies on PPV and fluid dynamics and understand them? The training grounds are a time to experiment with PPV and it's benefits, not on working house fires where lives are at stake......

Thanks,
Brian

Permalink Reply by Art Zern on December 3, 2008 at 11:52pm

Brian,

Great start, I like the AEIOU acronyn. Your point regarding the NIST studies goes directly to my point about conducting the proper research and background work or due dilligence before deploying new tactical methods and techniques.

By the way, as a former truckie, I take no offense to your comments.

Off to a good start, thanks Brian

Permalink Reply by Mike Walker on December 4, 2008 at 10:30am

To echo what Brian has stated: We implemented PPV approximately 20 years ago. I cannot recall any major snafo's because of the tactic but I have seen close calls. Just like with many other tactics used on the fireground, we were guilty of using a tactic, (In this case, PPV), for every fire, regardless of the conditions. It became the, "What we always do", at every fire. As a result, some fires were not being ventilated adequately. The problems I was seeing continually were:

The fan being started prior to an adequate exit opening being created
The fan being used because the Truck company was too lazy to get up on the roof
The fan being used because the Truck company could throw the fan quickly and then go steal the nozzle from the Engine folks
The fan being placed too close to the door because the entry point happened to be on an elevated porch which inevitably resulted in the fan falling off the porch due to FF's moving it out of the way so they could enter the building to steal the Engine's nozzle

We also observed these problems:

Even though PPV was the vent method of choice, FF would still take out every window, thereby rendering PPV almost useless.

FF's incorrectly believing that just because a window was removed, an adequate exit opening had been created. Which if the bedroom door was open, may have been true... think about it

FF's removing the large picture window in the living room with the PPV fan just a mere few feet away at the front door. The recirculating effect from this, while quite impressive to watch, didn't lend itself to good ventilation. That is, if our goal was to actually remove the smoke from the structure and keep it out....

With all of that being said, it became quite apparent that we had to address proper ventilation techniques with some of our people, and we have.

What I emphasis to my people is that PPV is a suppliment to ventilation. If horizontal ventilation is working as we want, then PPV can make horizontal ventilation work faster but if we must keep in mind that once the choice to use PPV is decided upon that it must be monitored through out the incident. Meaning, The initial opening is as close to the seat of the fire as possible. Make it big and make it fast. Also there must be a path for the PPV fan and the exit opening that has all open doors. If the bedroom door is closed, we can remove an entire exterior wall and it still ain't gonna work.

Once the inital opening is made and the fire is brought under control, then smoke removal from the remainder of the structure needs to be accomplished. This is best done through a systematic approach. One room at a time, which only takes a few minutes per room. If we mistakingly open all exit paths at once then the fan
(s) looses it's effectiveness.

Also, if PPV is decided upon, the person starting the fan MUSt MONITOR THE EFFECTS THE FAN IS HAVING ON THE SMOKE! If smoke is still attempting to push from the entry point, the fan has to be shut off. Something is wrong and the problem has to be determined and fixed prior to restarting the fan. If this is not addressed, Flashover can be expected within seconds. This goes back to the ( "E" in the AEIOU and the "O" overpressurized)

PPV can also supplement vertical ventilation. We've been doing it for years with good success. Once the roof is opened and ceiling popped, PPV can expidite lifting the smoke substantially.

I've got much more I'd like to discuss but I actuall have to go work for a bit. Second Chapter to follow....

Permalink Reply by Art Zern on December 4, 2008 at 6:40pm

Mike,

Great post. I'll look forward to part 2. I am thinking of gathering all of the info from this thread when it runs its course and creating a "training bulletin" to post for interested parties. What do you think?

Thanks again for really good info.

Permalink Reply by Jeff Schwering on December 4, 2008 at 7:52pm

Hi guys, I thought I'd throw my two cents in on this one. At my old department I had the "pleasure" of watching PPV used in a training fire by a chief, who had been to a class and thought he knew the in's and out's. This was the beginning in St. Louis County. Result was the back-up line I was on, was placed into service to help get 3 brothers out, because the fire ate them up. This was a training burn I might add. Not a good first experience. With that explained the county has come a long way with PPV.Many dept's including mine, use PPV in coordination with other ventilation tactics. If I'm the interior officer, I call for our PPV fan to be turned into the fire building when I'm positive it will be effective. Policy states our fan comes off the engine and is started pointing away from the door until requested. PPV is an excellant tool in our big tool box, however, we must use it as a tool not as a crutch.

Permalink Reply by Mike Walker on December 4, 2008 at 8:37pm

Part Two:

As to setting the fan: When the fans are new, they tend to remain stationary when running. As the fan gets older and the mechanisms used to keep the fan in place don't work as well. If an older fan is going to be used, it should be monitored to make sure it remains in the desired direction. Interestingly, the more times a fan falls off of a porch, the faster the stabilizing mechanism wear out....

As to turning the fan off: It should be noted that PPV fans that run on gasoline work well to push out smoke but they do contribute to Carbon Monoxide. Expect levels of around 100ppm of CO from the fan. So with that in mind, once the smoke is gone, turn the fan off, unless you happen to like CO induced headaches. Many have mistakingly worked inside a house that is clear of smoke, without their SCBA's while the CO levels are significantly higher then safe levels. Remember, 25 PPM is acceptable for periods longer then 15 minutes. Levels higher then 25, require respiratory protection.

Going back to the concept that PPV "Suppliments" ventilation:
This get a bit complicated to explain but I'll give it a shot... If crews put all of their hopes of ventilation success on PPV and follow the rules of limited number of exit openings and there just happens to be more then one fire within the structure, and the fan quits for whatever reason, interior crews should expect an opportunity to urinate on themselves to develop rapidly.

As I think of more, I'll post it.

Permalink Reply by Jim Mason on December 5, 2008 at 12:30pm

Good choice on the discussion topic Art! Thank You for the start up!
If you get a chance to due an article or piece somewhere on it please mention our fine CSF discussion page in it so we get some more members!
We don't do PPV until the fire is knocked down and then it is usually, only in large commercial buildings, when the movement of smoke from heat differentials has been lost due to cooling. What I don;t understand about the PPV thing is this: When can we say there is no one inside? Even in "abandoned looking buildings" isn't it possiible to have some one in there? I've got a video somewhere were the companies on the scene pull a bum out, I think it was from somewhere in the midwest here. What I mean is this - what are the size up factors that tell us there is no one inside that has to be search for? For us, that situation is commercial buildings after the fire is knocked down.


Mike Walker said:

Part Two:

As to setting the fan: When the fans are new, they tend to remain stationary when running. As the fan gets older and the mechanisms used to keep the fan in place don't work as well. If an older fan is going to be used, it should be monitored to make sure it remains in the desired direction. Interestingly, the more times a fan falls off of a porch, the faster the stabilizing mechanism wear out....

As to turning the fan off: It should be noted that PPV fans that run on gasoline work well to push out smoke but they do contribute to Carbon Monoxide. Expect levels of around 100ppm of CO from the fan. So with that in mind, once the smoke is gone, turn the fan off, unless you happen to like CO induced headaches. Many have mistakingly worked inside a house that is clear of smoke, without their SCBA's while the CO levels are significantly higher then safe levels. Remember, 25 PPM is acceptable for periods longer then 15 minutes. Levels higher then 25, require respiratory protection.

Going back to the concept that PPV "Suppliments" ventilation:
This get a bit complicated to explain but I'll give it a shot... If crews put all of their hopes of ventilation success on PPV and follow the rules of limited number of exit openings and there just happens to be more then one fire within the structure, and the fan quits for whatever reason, interior crews should expect an opportunity to urinate on themselves to develop rapidly.

As I think of more, I'll post it.

Permalink Reply by Brian Arnold on December 5, 2008 at 3:26pm

Jim,
Using the AEOIU method, (I) if you can't confirm or deny a possible rescue then it's immnent. We use this approach on SFD but commercial structures, garden apartments, etc. are a whole new ball game. I've been on those large abandoned warehouse fires where they should be vacant only to have a bum hit the street bailing from the second floor. PPV is meant to be used when the odds tilt in your favor of known factors like Mike was talking about. Can we get a large enough exhaust opening, are the doors to the fire room open, has it not extended to the attic, what is the push from the entry point of the attack team as well as the push when the windows are taken out......thus my reasoning for limiting PPV to some pretty favorable conditions in a single family dwelling.

With commercial structures and my limited experience with high rise fires, the fan gets fired up after knockdown to get the cold smoke out. I would defer to those that make many more high rise fires than me as to the benefits of PPV in a high rise, although the studies show that it has some benefits.

I would pose another question to the group to tag along with the PPV conversation; do you know what the expected fire behaviour of the fire room should be when you perform any type of ventilation. ie. what happens to the BTU production and thermal layering with vertical, horizontal or PPV? How much time does each of these practices buy the attack team to make entry and get a knockdown?

And one last little tid-bit for you about PPA (positive pressure attack). Did you realize that each of the NIST studies recommend that the attack team delay it's entry until the signs of positive pressure can be witnessed coming from the exhaust? Estimated times 90-120 seconds in a holding pattern at the front door........I don't think too many firefighters would be willing to do this.

Brian

Permalink Reply by Mike Walker on December 5, 2008 at 8:52pm

Jim brings up a great point: How does one define "Imminent Rescue?"

As to the exact meaning intended by they guys who came up with this I'm not sure but to me the "Imminent Rescue" pertains primarilyt VES situations and situations where a layer of visibility still exists at the floor levels.

Why VES situations? Since that part of the search will be conducted on opposite side of the fire from the fire attack team, the increase of pressure inside the structure could blow a bedroom door open, which would then mean searchers are going to get blasted by heat. In VES situations, PPV is withheld at least until VES operations are completed.

To the floor level visibility issue: Good visibility may very well indicate clean enough air and cool enough air for victim survival. If the fan is started it will stir up the smoke and ofcourse the toxic gases therein. This could cause a tenable atmosphere to dissappear. Now mind you, I have absolutely no proof of this except for what I have visualized. I may very well be dead wrong about the layer of "CLEAN" air. My assumption that since I can see through it, then it must be clean could be wrong. The toxic gases could very well be at that level even before the smoke indicates that but I am basing my assumption on the fact that all of the gases are being heated and gases rise...

Otherwise, when smoke has already infiltrated the entire space, my logic tells me that any effort to remove that smoke would in fact be benificial to a victim.

Like we always say to our students, we have to let the situation dictate our tactics. The fires that don't exhibit heavy smoke conditions, PPV is a great tool because it shortens the amount of time smoke is in the building, thereby reducing property damage. The fires that are heavily charged with smoke may be best served by other forms of ventilation. However, there could very well be instances were a blower could be placed and it would be at least one minute before attack crews are ready to enter.

I am of the notion that ventilation can, and should be broken into two phases. Pre-Control ventilation should administered in such a manner that will give a trapped victim the greatest chance for survival by removing contaminants and also by improving the environment so that Fire-Attack crews and Search crews can maintain interior operations. Then Post-Control ventilation is implemented to remove smoke to reduce property damage and improve the environment for Salvage and Overhaul operations.

Using PPV in a High-Rise is a must, again in my humble opinion, in many situations. Evacuating victims must have an exit path that is smoke free as much as possible. Pressurized stairwells are a great concept but I have my doubts that the building system will be able to keep up during the peak of evacuation because of the number of doors that will be open. Therefore, a blower, preferably an electric blower, can provide significant augmintation to stairwell pressure needs.

Permalink Reply by Scott Kleinschmidt on December 6, 2008 at 1:03am

OK,
Here I go don’t beat me up to bad. To me PPV is for after a fire is out and I want to augment the removal of smoke. PPA is what happens when I use a fan under active fire conditions while the attack is underway.

PPA: To many things have to be just right for this to be productive and a lot of stuff can go bad when not done right. If this is going to be used make sure crews are trained in it’s use

PPV: at least the way we have done it the past 20 years. Our operating procedures are the first due CO makes a “hot lap” on the structure while crew is pulling a line and charging it. He will take the windows on the fire room and start the vent. He will then hook up with his crew and they will make entry and hit the fire room. Once he has a knock on the fire he calls for the fan. PPV pushes out remaining smoke and heat.

This works well on the little fires. What happens a lot is as Mike said “windows get taken out and we have a hard time using PPV”. This is the problem with PPV( at least how we use it) I am venting after the fire is out. FA and Search crews looking for relief are almost always going to take windows. So technically we are really doing horizontal venting and then augmenting with a fan.(PPV).

The problem is, some crews are taking a beating and putting themselves in bad spots because they don’t want to break windows and screw up the PPV.

We have really started to push the importance of good adequate quick venting. This is done either horizontally or vertically. Get it venting then as it cools down use a fan to clear remaining smoke. We tell guys don’t be concerned with breaking windows if they need taken and they are in the right spot to “help” attack crews. 80% of our SFD are easy vert vents. 6/12 or less and we have started back with pushing this type of venting if warranted. Most times anything over a small room and contents is warranted.

Regardless of the vent choice it is always coordinated with FA.


We do tell guys that when they introduce PPV to make sure and not cone the entire opening leave a gap at the top of the door ( this is for if the structure is not “ready” for the introduction of air) it will let them know to shut it down when smoke comes back over the fan air going in. We also tell them make sure the exit is at least 2 times the opening. This is a hard habit to break because most guys were taught ( old school thought) in the academy cone the entire door and exit opening ¾ to 1 and ½ the entry opening.

I know at least here the fan became a crutch not a tool and lead to poor decisions in venting.


Scott

Permalink Reply by Brian Arnold on December 6, 2008 at 10:56am

Scott,
Can't beat you up too bad over anything you stated. You guys are aware that there are major differences between PPV and PPA even though the fan gets used in both. There is a time and place for each, but the FAN doesn't take the place of normal truck company operations and sound ventilation tactics.

Brian

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