Ventry 20EM3550 Owner's Manual - Right!
P
OSITIVE
P
RESSURE
V
ENTILATION
F
ANS
7
HOW TO USE POSITIVE PRESSURE VENTILATION
PPV The Basics
Positive pressure ventilation (PPV) is a powerful tool for firefighting but, like a double-edged
sword, it can cut both ways. Training and careful planning are essential if PPV is going to work
to its full potential. Remember the basic fire triangle (heat, air, fuel). PPV reduces the
temperature by displacing the hot flammable gasses, but it also provides the fire with an
abundant source of oxygen. Timing is the key: have everything ready for the initial attack
before positive pressure is used. The size-up needs to be done, incident command needs to
develop a plan which uses an aggressive initial attack, lines need to be setup and charged, and
firefighters in SBA’s need to be ready to attack the fire seat.
Use PPV to blow the heat and smoke out of the structure, then get in and put the fire out before
the increase in oxygen has a chance to let the fire flair up. Figure 21 is a simple example of the
fan's proper use.
The size-up should look for exterior signs that indicate the fire seat's probable location. Use that
information to develop an initial attack plan that ventilates by pushing the heat and combustible
gases out of the structure near the seat of the fire.
In actual practice it is not always possible to locate the seat of the fire during the initial size-up.
In such cases, we've found that using positive pressure at the most convenient point of entry and
venting on the opposite end of the structure works well. If possible, take into consideration
which way the atmospheric wind is blowing, especially a strong wind, because working with the
wind is more effective than trying to overpower it.
After the initial attack, positive pressure can be used to minimize smoke damage. Pressurize the
structure starting at an upwind room. Open a window and let the room completely clear of
smoke. Then close the window and entrance to that room. Proceed in a downwind direction to
clear the rest of the rooms in the structure. The downwind technique prevents smoke from
leaking back into rooms that have already been cleared and allows you to check for other fire
seats; if an upwind room refills with smoke, you've got another fire seat to deal with.
Figure 21. Proper Fan Operation