A Positive Change in Fire Testing – The Positive Pressure Fire Test

Frames, doors and the hardware attached to the opening are crucial components to limiting the danger and damage that can occur in a fire.  Having a fire rated opening in a facility, especially in hallways and stairwells, helps ensure people can safely move past the fire on the opposite side of the door, without being harmed. Fire rated openings are tested to measure the ability of that opening to prevent the spread of fire. By compartmentalizing the fire, the opening provides a barrier allowing building occupants to exit the building and the fire to stay contained.

There are two ways to test fire rated doors: positive pressure and neutral pressure. When a fire first begins, smoke and pressure form at the top of a room, filling about 1/3 of the room’s total area. The fire is fueled by air entering the room from the top and bottom of the opening because the fire is trying to suck in any available oxygen. Positive pressure begins to build forming a neutral pressure plane, which is the area between the positive pressure above the door and neutral pressure below the door.

Positive Pressure testing diagram.doc

The neutral pressure test, the previous standard form of testing, locates the neutral pressure plane in the space over the door.  Heated gases rise from the test furnace and escape through an overhead venting system.  However, this test does not account for closed room environments. Whereas, its next of kin, the positive pressure fire test, reproduces real life fire conditions in a lab environment. In the positive pressure test, the neutral pressure plane is lowered to 40” above the door’s sill (bottom of the door), forcing the heated gases to seep through unsealed gaps around a door.  This method allows for an exchange of gases between both sides of the door, which more relates to real life fire situations. Without lowering the neutral plane to the 40” above the door’s sill, the heated gases would always rise, and the fire forever feeds on the air seeping in from the opposite side of the door.

Furthermore, fire rated openings with a wood door that are rated over twenty minutes are required to have an intumescent seal, which expands when heated to prevent air from entering the space around the door’s edge. This seal is only needed for positive pressure testing, since the neutral pressure plane is lower. Therefore, the seal is required for fire-rated labeled openings, since the positive pressure test illustrates realistic circumstances. The hope is for the seals to allow the heat and fire to dissolve due to a lack of oxygen, and the fire would never interact with the other side of the door.

Through many years of testing, we can be assured that the positive pressure test is accurate to real life conditions therefore providing hope for protection, survival, and sanctuary.

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