Mechanical ventilation

Question 1

Define Positive Pressure Attack (PPA)

Answer 1

Using high output fans in order to pressurize the inside of the building relative to atmospheric pressure carrying smoke toxic gas and heat from the entrance where the fan was placed to an exhaust.

Question 2

Define Positive Pressure Ventilation (PPV)

Answer 2

To make the area more tenable and to clear hazardous gases and smoke from the structure.

Question 3

Define Positive Pressure Pressurization (PPP)

Answer 3

Using high output fans to overpressurize and enclose compartment preventing additional smoke toxic gas and heat from entering the area.

Question 4

Flowpath

Answer 4

The volume between an inlet and an outlet that allows movement of heat and smoke from the high pressure areas within the fire towards the low pressure areas accessible via doors and windows.

Question 5

Positioning options for high output fans

Answer 5

Single (basic setup)
Series (30% more air)
Parallel (wider openings)
Combination (Wider openings)
V-point (highest air volume)

Question 6

Purpose of PPA

Answer 6

Reduce the risk of backdraft or flashover. To make an area more tenable for victims and firefighters. To enable cruise to advance more rapidly to the seat of the fire. To help protect firefighters who are extinguishing the fire by removing Steam and other products of combustion.

Question 7

Examples of situations which PPA might be preffered.

Answer 7

Conditions are untenable for firefighter entry due to heat smoke and toxic gas.
The construction is unsuitable for natural ventilation due to the lack of vertical shafts or horizontal exterior openings.
The fire is below ground level in a confined space or where it is difficult to gain entrance.
The incident Commander deems PPA advantageous.

Question 8

When is PPA inappropriate?

Answer 8

Signs of impending backdraft are apparent. The fire location has not been established. Potential exhaust openings are out of reach or otherwise inaccessible. The wind direction and velocity would make PPA dangerous or ineffective. There are victims in the exhaust opening. The exhaust opening has been used for rescue or maybe needed for rescue later on. There are exposure issues that cannot be controlled. Caution should be exercise when using PPA during an attic fire or situation or structural components have been impinged on by fire. The incident Commander deems PPA disadvantages.

Question 9

Steps for setting up PPA

Answer 9

1. Locate the fire. Be aware of multiple ignition points, which are common with arson fires. If the fire cannot be determined PPA should not be used.
2. Advanced a charge line into the entrance.
3. Bring one or more high output fans to the entrance. Position them sideways at a 90° angle to the door. Turn on the fans to ensure they are working and leave them idle.
4. Advanced a charge line to cover the plant exhaust opening.
5. Make an exhaust opening as close to the fire as possible. The size of the opening should be approximately 3/4 to 1 and 3/4 * the size of the entrance. Larger is better.
6. Upon direction turn the fans to face the entrance. Wait 30 to 60 seconds to allow the flow path to become established and stabilize. Check that the cone of air completely seals the entrance, the fan must be monitor at all times.
7. Obtain a report from the supervisor at the exhaust opening who is assessing the effectiveness of the ventilation. Assess the effectiveness of ventilation at the entrance opening.
8. If the ventilation is effective proceed with fire attack.
9. Continually monitor ventilation at the exhaust and the entrance to ensure effectiveness.

Question 10

Improper PPA can result in what?

Answer 10

If the door is not completely sealed or the exhaust opening is inadequate, convection May occur, leading to a more rapid onset of flashover.
If the exposure line is directed into the window rather than across it, it may render the PPA ineffective and it may spread the smoke and fire into the interior crews.
If the exhaust opening is not monitored, nearby exposures and personnel may be put in danger by the fire smoke and heat coming out of the exhaust opening.

Question 11

Purpose of PPV

Answer 11

Make an area safer for salvage and overhaul.
To make salvage and overhaul efforts more effective.
To remove toxic, explostive, and superheated gasses.
To decrease property damage.

Question 12

What is the purpose of PPP?

Answer 12

To prevent toxic, explosive, and superheated fasses from spreading to exposures.
To confine the fire.
To protext exposures.
To decrease propety damage.

Question 13

Example situations for PPP

Answer 13

Prevent fire extention into the adjacent occupancies in a strip mall.
Confine a garage fire and pressurize the adjoining house.
Confine an attic fire and pressurize the rooms below.
Prevent fire extension to an adjacent house (townhouses).