David A Greene - Published Writing Summer 2007

David A. Greene

Published Writing - Summer 2007

(From Carolina Fire-Rescue EMS Journal - Summer 2007)

Ventilation is certainly one of the least trained on and most important functions that occur during a structure fire. Ventilation, as defined by the IFSTA Essentials Manual 4^th Edition, is the “systematic removal of heated air, smoke, and gases from a structure and replacement with cooler air”. Chief Bruno (Alan V. Brunacini) once joked that he attended a shed fire in Phoenix at which Truck 6 cut a four by four hole in the roof of the eight by eight shed. The Captain from Truck 6 said, “Chief, if it’s got a roof, we’re gonna open it.” Bruno said after seeing Truck 6 operate, he “went home and sprinklered (his) house.”

Given the new synthetics and fire loads that we encounter in “average” structure fires today, associated with the better protective clothing allowing us to penetrate deeper into the structure, we often don’t think about aggressive ventilation to improve visibility and decrease the chances of flashover occurring. As a result, we are playing a game of proverbial Russian roulette. Although vertical ventilation is ideal, the building construction may not allow for this. For example, if your crew is entering a singlewide microwave (mobile home), do you want two truckies on the roof that is only supported by two by two’s, probably not? This is where horizontal ventilation comes in to play, more appropriately, forced positive pressure horizontal ventilation.

Described as the “wave of the future”, “a giant step forward in firefighter safety”, and “the greatest innovation since the introduction of breathing apparatus” by some in the mid-80’s, positive pressure ventilation (PPV) has made a big impact on the fire service. However, as with every new tactic or piece of equipment that comes along, we must have an understanding of its function prior to utilizing it.

PPV works by creating a seal over the ventilation inlet and pressurizing the structure while forcing massive amounts of clean, cool air inside the structure it pushes the combustible, heated air outside through the ventilation outlet. When utilized properly, it creates a cooler, more visible environment for the interior crews. When utilized improperly, you should thank God that you get to leave the scene in the front of your engine and not the back of your ambulance. As with all new tactics, we cannot just throw the equipment on the engine and keep it locked up until we decide it is time to use it.

First and foremost, you need to have a written plan of when to use PPV and train everyone on its use. A disadvantage of PPV is that it will likely intensify the fire, particularly those that are fuel controlled or under-ventilated. Consider any trapped victims inside the structure. There have been many scientific studies that indicate that heat flux is often increased temporarily when utilizing PPV. Therefore, PPV must be utilized very carefully when victim locations are unknown or the victim may be between the fire and the ventilation outlet (exhaust). A Battalion Chief in my department often calls for PPV once firefighters have reached the seat of the fire; others in my department start PPV as the interior crew is entering the front door. Timing is critical. Once PPV has begun, it will most likely cause a compartment fire to burn with greater intensity. Compartment temperatures may even rise prior to the continual introduction of cooler air. Therefore, hose lines must be in place prior to initiating PPV.

When utilizing PPV at the scene, always create an exhaust point (or ventilation outlet) in the structure near the area of involvement. This should be roughly the same size as the ventilation inlet. As a general rule, if you set the fan up at the front door, then open the back door. This is a critical step that is often missed. Without making a ventilation outlet, once the structure is pressurized, the ventilation inlet will often become the outlet also. This may present a surprise to the interior crew who is searching for the fire. Their search will certainly be over once the fire passes over their heads and begins involving the doorway through which they just entered. As a general rule, surprises on an incident scene suck!!! Therefore, always insure that you have a ventilation exhaust point (outlet) prior to initiating PPV.

PPV fans should be set up far enough from the ventilation inlet to form a cone around the outside of the inlet. This cone causes a seal that allows the structure to be pressurized. Too often, PPV fans are placed on the threshold of the doorway. This not only creates ineffective ventilation but also hinders egress should conditions deteriorate and rapid evacuation be necessary.

Always insure that PPV is set up at the interior crews’ backs so that the forced air movement is in the same direction that the interior crews are moving. If you think someone operating a hand line in your direction while inside is “troublesome”, try competing with the movement of 26,000 cubic feet of air per minute in your face. It may make that inch and three quarter hose line you are holding feel like a garden hose. PPV fans should always be set up on the unburned side to direct the air movement toward the burned side, the same method we use for fire attack.

Ask anyone who has ever used PPV what the most annoying side effects of its use is and they are likely to answer with, “WHAT??” Most gas-powered fans generate a tremendous amount of noise, which makes face-to-face communications in the area of the ventilation fan impractical if not impossible. This is something everyone operating on the fire ground needs to remember. It makes the statements, “I need a pike pole to pull the ceiling” and “I’ve lost my partner,” sound exactly the same when spoken at the front door four feet in front of the ventilation fan. Interior crews should have portable radios and the incident commander should be somewhere they can hear their radio over the noise of the fan.

Very large structures often require more than one fan to obtain a seal and produce enough air movement to properly ventilate. Consider this whenever you are thinking of your first due units. It may take more than one alarm to get enough PPV fans at the scene. If the building is too large to ventilate even using multiple fans, consider vertical ventilation.

Remember there is a time to turn the PPV fan off! Many years ago, I was attending a fire in a large house of ordinary construction. The interior crews made a “good knock” on the fire but it got into some void spaces and got above and behind them. Typically when this occurs, hard-nosed firefighters will attempt to regain control of the fire despite deteriorating conditions and will remain in the hazard zone even as the building is literally falling down around them. Transitional operations are funny that way, everyone wants to be involved with the “blitz attack”, that is exterior attack with large caliber hose lines transitioned to an interior attack, but when you transition from interior to exterior, no one wants to play. In this case, the Incident Commander was very proactive and was quick to pull everyone out just as a good portion of the structure flashed over and a partial collapse occurred. The IC’s crystal ball was working well and he moved “the troops” out of harm’s way as conditions deteriorated rapidly. However, 20 minutes into exterior operations, the PPV fan was still running full-tilt pouring air into and extending the fire throughout the structure. We should never operate PPV fans unless we have hose lines in place and are operating inside the structure.

During overhaul, PPV fans can help to insure a relatively clean atmosphere in which to work. Keep in mind that the level of the products of incomplete combustion including carbon monoxide can be effectively reduced by the use of PPV during overhaul. However, if a gasoline powered PPV fan is being used, it will reach a point where it is distributing as much carbon monoxide from its own exhaust throughout the structure as it is removing from the structure, yet another point where the fan needs to be shut off. If you’re ever in doubt, you can check the level of carbon monoxide using air-monitoring equipment. Just don’t try to detect carbon monoxide by counting the number of fire fighters with headaches and nausea; most of us need all the brain cells we can muster.

Conversely, there have also been cases, one of which was in the last several years, where a fire was knocked down, a PPV fan was initiated, and then conditions became untenable. In this case, the attack crews were between the fire and the ventilation exhaust (outlet) and, in a matter of minutes, conditions went from good visibility to zero visibility and the interior crews became trapped in the basement. The two firefighters that entered the basement for rescue purposes, encountered such severe fire conditions that they retreated to the front lawn of the house and had to immediately remove their protective clothing because it was on fire. Tragically, one firefighter was not removed until approximately 90 minutes later. He was transported to a local hospital where he was pronounced dead. Remember that positive pressure ventilation must always be closely coordinated with attack.

Positive pressure ventilation is a modern technique that if well trained on and practiced, can be a benefit to firefighters operating in the hazard zone. As our war with fire wages on, we must continue to be proficient in these techniques and the appropriate application of positive pressure ventilation will continue to be a useful tool in our arsenal for each battle.

Be safe and do good.

References: www.firetactics.com/ppv.heat.flux.htm