Making the attack positive
Positive Pressure Attack (PPA) is a useful tactic to have for structural firefighting. Before we get into the discussion of the when and how to use PPA we should make sure we have a clear definition of what PPA is. Positive Pressure Attack is the coordinated tactic of applying Positive Pressure Ventilation (PPV) during an offensive interior fire attack. Before PPA is used as a tactic, personnel should be familiar with their SOP’s/SOG’s on using PPA for structural fire control.
Using safe procedures are needed to maximize the safety of both fire personnel and victims during offensive firefighting operations. PPA can be used when the need for an aggressive fire attack is needed to stabilize the incident.
To understand how PPA will assist the fire crews by changing the natural flow path of fire within a structure. Once firefighters have moved into position and open the door to make entry, attack crews will change the flow path of the fire. Fire will now move towards that opening because the pressure that is created in the fire compartment is higher than the pressure found outside the compartment. This means that when firefighters enter the structure they are now in the flow path of the fire, bringing all the products of fire towards interior crews. Any victims that are between the fire and the entry point will now be subject to additional heat and smoke conditions. Firefighters can improve these conditions by using PPA. A positive pressure attack will change this flow by increasing the pressure at the entry point. Giving the products of combustion a controlled path to the exterior of the structure.
Now on to the benefits of using PPA. Positive pressure attack rapidly removes the products of combustion, making it easier and safer for crews to advance to the fire compartment. The fire’s ability to spread is reduced because the heat and smoke (which are fuels) are removed from the structure. Search and rescue efforts are helped because visibility is improved making it faster to search areas of the structure. Victims now have clean cool air replacing the fire gases, increasing the chance of survival. Last, PPA can help to reduce damage caused by heat and smoke.
The procedures to make a positive pressure attack can vary from department to department but they should include some of the same basic tactical procedures. The first step in using a PPA for your attack method is to determine the entry point for the fire attack team. This entry point should be on the unburned side of the structure and is where both the attack and ventilation teams are to enter. At this point, a firefighter should be assigned to get and operate the positive pressure ventilation fan (PPV) during the operation. Once the PPV fan is brought to the opening it should be started, turned away from the building and left idling till the command calls for PPA. As the officer-in-charge performs their 360 they should determine the best exhaust point. This should be as close to where the fire is as possible. A team is now directed to be in charge of creating the exhaust point and wait for command to call for it to be opened. The team should also be equipped with a hose-line if there are exposures. Once the fire attack team is in place with a charged hose-line the exhaust opening can be made. The entry door should be opened and the PPV fan placed into position. The PPV should be placed in a position that the fan produces a cone that encompasses the opening. The fire attack team should wait to enter until they see a change in conditions (this normally only takes a few seconds). If fire intensifies in the ceiling at the entry point, this is a sign that a catastrophic fire event may occur and the use of PPA should be stopped. This can be an indicator that the exhaust opening is too small or that there is an opposing wind. Once the fire is extinguished, overhaul should be immediately started due the danger of the fire reigniting due to the use of the PPV fan supplying additional air to the fire room. The use of thermal imaging cameras is strongly suggested as part of any overhaul.
The following are some of the tactical considerations for the use of PPA. The size of the exhaust opening is very important to ensure the products of combustion are exiting the building and that the PPV is not just increasing the size of the fire. The exhaust opening should be between half to twice the size of the inlet opening where the PPV is placed. If the exhaust opening is too small, a flashover could occur and if it’s too large the products of combustion will not exit the building effectively. Ensure that ventilation openings are controlled. Do not allow for several openings to be made in the structure because you will not be able to pressurize a structure which has had the multiple windows removed. Do not let fire personnel block the flow path of the PPV. Doing this will only reduce how effective the fan will be.
Dos and Don’ts of Positive Pressure Attack
- Use windows for exhaust openings. Using a door could bring heat down to the floor level causing victims to be burned.
- Perform PPA from the unburned side of the structure.
- Ensure communication is clear on when to direct the PPV into the structure.
- Ensure that the exhaust opening is open before the PPV is directed into the door.
- Watch for worsening fire conditions. If conditions start to get worse then back crews out of the structure.
- Wait approximately 10 seconds before entry is made to see what fire conditions do.
- Be prepared for the fire to exit the exhaust opening. The need to place an exposure line at this opening may be a consideration to protect exposures.
- Don’t use when signs of backdraft.
- Don’t use when victims are hanging out of windows waiting for rescue.
- Never enter under thick, turbulent black smoke, this is a sign of flashover.
- Never have an exhaust opening where a strong wind could blow from that side.
So in summary, positive pressure attack is a useful tool for any fire company to use when it is used correctly. Positive pressure attack can be an effective tool for increasing the survivability of victims in a structure fire. Fire attack crews will notice that not only is it a cooler but they will also have increased visibility. A strong command presence is needed due to multiple activities being performed at the same time. As with any other job performed on a fire scene, positive pressure attack should be performed in training before it is used at an emergency scene.
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