If you’re a regular reader of Quick Drills, you know we spend most of our time in this column covering the basic fireground and rescue skills that each of us need to be good at our jobs.
This month is no exception. We’re going back to the basics of positive pressure ventilation (PPV). PPV came to the forefront in the 1980s from the West Coast and was a hot topic of discussion into the 1990s. Today, you can see PPV being used by many departments around the country and around the world.
The buzz around PPV continues due to the work by various research groups studying the effects of PPV on fireground operations. These tests are similar in their scientific grounding to the modern fireground fire behavior research released in the last couple of years by UL and the National Institute of Standards and Technology (NIST). The results of the PPV tests should be available in early 2014.
In the meantime, however, we can train on what we already know about PPV. This article focuses only on using PPV to remove smoke and fire gases because I don’t have the space to cover all the aspects of PPV. We could write volumes on the topic and still not cover everything.
First and foremost: PPV is a tactic, and like all tactics it has to be used only when appropriate. Any tactic can backfire on you when used incorrectly or at the wrong time.
At any fireground operation, a comprehensive 360-degree survey of the building will provide you with the best information to base your decisions on. That same process should be used before initiating PPV for smoke and heat removal.
When conducting the assessment, try to identify possible locations for the inlet opening for fan placement and the discharge outlet and flow path between the two. Also consider smoke conditions and the building construction type of the involved building. Caution should always be used when fire may be hidden in the walls or void spaces, because the hidden fire could be inadvertently fed additional oxygen, causing it to extend if not properly monitored. This is especially true in balloon-frame construction.
Always provide continuous size-up during PPV operations and have handlines in place to suppress any flare-ups as they occur.
Our ideal inlet opening would take advantage of the prevailing winds, but it doesn’t always work that way. If you can’t take advantage of the prevailing winds, select the opening that provides the best opportunity for airflow.
A longstanding principle of PPV has been to form a seal around the inlet opening. The seal acts to prevent the back pressure from pushing out, just like blowing up a balloon. Forming a seal requires setting the fan back from the opening; we were taught to look for smoke pushing out of the opening normally at the top, where the seal is more difficult to form.
There’s a movement among those who are teaching PPV to change this longstanding principle, and rather than forming a seal around the inlet opening, focus on forcing as much air inside the building as possible. This change, while not accepted by everyone, is creating changes in the design of some PPV fans. Fan shrouds are available that direct air in a tighter cone when it leaves the fan.
The bottom line: As the science of PPV continues to develop, make sure you stay informed, but follow your department’s guidelines for fan placement at the inlet opening.
Ideally the discharge opening should be at a point closest to the fire and should be as high as possible in order to clear as much of the building as possible. There are always exceptions to this based on how much of the building has to be cleared. Example: a food-on-the-stove fire fills the kitchen and dining area of the house with smoke. Opening the back door onto the patio or a kitchen window will normally quickly clear the charged area. Note: Firefighters should avoid operating between the fire and the discharge point.
Since we must use the openings that are provided to us in the form of windows and doors, try to select openings that you can control the size of, such as a sliding glass patio door.
The discharge opening can be up to 1½ times the size of the intake opening, but again, you can only use what’s available to you. Also, it’s best to open the door or window, rather than breaking the glass, but this too will be based on the conditions present and the incidents and actions taken before the beginning of PPV operations.
Control the Air Flow
Air is just like water in that it follows the path of least resistance as it moves from one area to another. Our PPV operations are greatly improved if we control the air flow from the inlet to the discharge by opening and closing doors to enhance air movement.
As you size-up the interior of the building, look for areas that have not been affected by smoke and close those areas off if possible. This minimizes damage that could be done by the smoke and reduces the size of the area that the PPV operation has to work to clear (more air in fewer square feet), which speeds the clearing process.
Also, by opening an interior door you can quickly clear an area, close the door, then move to another area, provide a discharge opening and clear it, then repeat the process until conditions inside the building improve.
Gas vs. Electric
Depending on where you’re located in the country, you may use the term “fan” or the term “blower.” Fans suck air out; blowers push air in. For all intents and purposes, however, they’re the same thing. Gasoline-driven PPV fans are by far the most commonly used fan on the market today, but the electric blower is becoming increasingly popular as well. Both have pros and cons; the most important thing is knowing your equipment.
If you’re using a gas-driven PPV fan, remember that it’s producing carbon monoxide (CO). Wear proper PPE and ensure that air monitoring is in place to watch for dangerous levels of CO.
The electric PPV fan offers a cleaner air flow that provides better results at certain incidents, such as the food-on-the-stove example. By using the electric fan we don’t add the exhaust fumes associated with internal combustion engines. The electric fan will also add cooler, cleaner air during the overhaul and investigation process than the gas unit, with less noise.
Master the Basics
Positive pressure ventilation is a proven, sound fireground tactic that will improve your department’s operations, but like everything we do on the fireground, it requires us to understand and master the basics to achieve success.