John Kriska,
Chief,
Rock Hill (MO) Fire-EMS Department
Vertical ventilation is necessary when the situation mandates that method of ventilation, but to “automatically” send firefighters to the roof to open it up seems to me to be a little dangerous … and very time consuming. If the incident does not call for vertical ventilation, then it seems to me that horizontal ventilation will work just as well. It is safer and easier to implement.
I am an instructor of PPV at the University of Missouri Fire and Rescue Institute, and I have found that if you are attempting to implement PPV in a building and have an electric fan in the exhaust opening to assist the PPV by pulling out the smoke, all you would do is slow down the process. Why? A 16-inch electric fan can move about 5,200 cfm of air. With an exhaust opening that is at least three-quarters the size of the pressurization opening, you will move much more than 5,200 cfm. An electric fan in the exhaust opening serves simply as a “blockage.”
If fire has entered the pipe chases, it is already spreading without the use of PPV. Until such time as firefighters open up the pipe chases and apply water to the extended fire, the fire will continue to spread. In buildings of balloon construction with fire in the basement, extension probably is already heading into the attic space before the first pumper leaves the engine house. If fire has penetrated through the ceiling and has gotten into the attic space, the fire has already “spread,” even without the use of PPV. With or without PPV, the acceptable tactic is to open up the pipe chases in the fire area and check the floors above for fire extension in the pipe chases. When dealing with balloon construction, get a line above the fire to check the walls and attic. For fire that has penetrated the ceiling, open up the ceiling.
However, in my experience, the important function of opening up the concealed spaces is normally delayed, allowing the fire to continue to spread. Why the delay? At this point, “the way we have always done it” calls for someone to say “we need ventilation”; it can be hydraulic or mechanical. This takes time! But by using positive pressure attack (PPA), ventilation takes place immediately, allowing for efficient operations in decent visibility. If using PPA for up-front ventilation, you don`t need to set up smoke ejectors; another crew can follow the attack crew and immediately begin opening up these concealed spaces the minute the fire is knocked down. Why? Because ventilation is already in progress clearing the space of smoke, steam, and heat. In my opinion, the key element here is time.
PPV must be used correctly. The seat of the fire must be identified, and an exhaust opening must be made in that area. You must give the products of combustion somewhere to go other than to follow the path of least resistance, which–without an exhaust opening–could be directly toward advancing firefighters.
In my jurisdiction, I have witnessed at an uncontrolled school fire PPV`s pushing fire back into the fire area and holding it in check until the attack crew applied water. This was not planned; however, that is exactly what happened.
We also had a situation in which the fire was in the basement and extending to the first-floor family room through openings around the heat ducts. When PPV was introduced, it pushed the fire back down into the basement and toward the exhaust opening made by the company officer.
Our first use of PPV was in a basement fire with a report of a trapped person. The company officer`s exterior building size-up revealed that about 50 percent of the basement was involved in fire. In his judgment, if someone were still in the basement, he would be written off because of the extent of the fire. However, he felt that an individual could have made it to the first floor. Therefore, his action plan was to conduct a primary survey of the first floor. He ventilated the basement by making two exhaust openings in the area of the fire and then introduced PPV by way of the front door. He and his pipeman were able to conduct a quick primary survey of the first floor. This was done with a smoke ceiling of about three to four feet, which allowed them to stay on their feet and look below the smoke ceiling. It was later determined that the fire was initially extending up the basement stairwell–not unusual. However, when PPV was started, it pushed the fire back into the basement and out the exhaust openings. Smoke on the first floor followed the same path. The attack on the fire was made by advancing the line down the interior stairs with good visibility and reduced heat. Why did this work so well? Because the company officer understood the basic concept of PPV–simple high school physics. He also followed the department`s standard operating procedure (SOP) for using PPV during the fire attack.
The key to successful PPV operations is training, training, and more training. All personnel must understand the basic concept of PPV. They use it every time they fill an SCBA cylinder. A written SOP is also an absolute requirement. As my Dad, a 34-year veteran of the fire service, constantly told me, “There is a time and a place for everything.” This advice applies to PPV. Our fireground decision makers must recognize that PPV is not the answer to all our firefighting problems. It is just another tool that, if used correctly, can help to ensure firefighter safety. Recognizing when it can and cannot be used is part of the training.
