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  Program 11
   
 

PPT1HRB - How Positive Pressure Changed Architectural Hardware

DHI CEP Program #10-1123

   
       
 
     
 

LEARNING OBJECTIVES

Part 1 - Positive Pressure Testing

Part 2 - Why Test?

Part 3 - Who is Impacted?


 

<< Glossary of Terms >>

 

Part 1 - Positive Pressure Testing

Description
Fire doors are tested by the Underwriters Laboratory (UL) and Warnock Hersey (Intertek Testing Services) to ensure they provide adequate protection of both life and property. The entire opening, including hardware is tested.

Since the fire test is designed to measure a door's ability to contain the spread of fire, the possible acceleration of combustion and breakdown of the door's ability to contain the fire could compromise a previous rating and require some redesign of non-conforming products. Thus, in 1997, the International Council of Building Officials (ICBO) approved a change to the Uniform Building Code (UBC) that requires fire doors be tested under positive pressure instead of neutral pressure.With positive pressure testing, the neutral pressure plane is lowered to a standard 40 inches above the finished floor, so regardless of door height, the neutral pressure axis is defined from the floor upward.

Most recently, many code groups across the U.S. have adopted the International Building Code (IBC), which also contains the requirement for positive pressure testing.

Old test method (UL 10B)
UL 10B test standard - Neutral pressure plane above the door

  • Ambient air is drawn into the test chamber around the entire door (top and bottom)
  • Hot air and gasses are released by a damper

Historically, the fire door test method placed the neutral pressure plane at the top of the door, regardless of its overall height. Everything below the top of the door was under negative pressure, and any gasses or products of combustion were drawn into the test environment or furnace.

With positive pressure testing, the neutral pressure plane is lowered to a standard 40 inches above the finished floor. So, regardless of door height, the neutral pressure axis is defined from the floor upward. The effect of this change places a very gentle amount of pressure against the remaining portion of the assembly, which may push smoke, hot gasses and any potential flames around the perimeter of the door assembly.

To envision the difference, imagine a closed door with a fan pulling the air away from the opening on the fire-side of the door. Now, reverse the fan so it blows against the door. In either case, the pressure isn't that great and certainly will not affect the structural integrity of locks, latches, hinges or frame anchors. However, with the fan blowing against the door, the products of combustion are not drawn away as they were when the fan was pulling air away from the door. If the face of a wood door is burning, the effect of positive pressure is to enhance combustion somewhat, and to drive the smoke, gasses and possibly flames through any leakage at the door perimeter. Under the previous test, these products of combustion were carried away.

New test method (UL 10C)
UL 10C test standard - Neutral pressure plane is 40 inches above the finished floor

  • Damper added to control a neutral pressure plane at 40 inches above the finished floor
  • Ambient air is drawn in from under the door
  • Hot air and gases are forced out at the top of the door
  • No flame detected on non-fire side of door for more than 10 seconds

To understand how doors are now tested, let's go over the old test again. Air was allowed to enter the room around the bottom and the top of the door. All the positive pressure and heat that were built up in the room were exhausted out of the top of the room. This is like opening the damper all the way on your fireplace at home. No smoke or pressure comes into the room, all the smoke and gas goes out the chimney.

So, if you think of a closer (or a top latch of a vertical rod) mounted on the top of the door, it is cooler than the other hardware located below it because air is coming into the room from the outside and cooling off the closer or latch. The neutral pressure plane, the plane of separation between the positive and the negative pressure, is above the door. Thus, none of the hardware was affected by the pressure built up above the door. The hardware was only exposed to the heat from the furnace jets, not from any pressure built up in the furnace.

In the new test, a damper is added at the bottom of the furnace. Air is still allowed to enter the fire at the bottom of the door, by the threshold. While no air is allowed to enter at the top gap of the door, some air is still allowed to exhaust by a damper. This is like your fireplace at home with the damper opened about half way. Some smoke goes out the chimney, but a lot of smoke and pressure comes back into the room.

Similar to real fire conditions, this is how the new test works. The neutral pressure plane is established at 40 inches above the finished floor. This is regulated by the amount of air that is released and entered into the furnace through the dampers.

Actual fire scenario
At the early stage of a fire, smoke and pressure forms at the top of the room filling approximately 1/3 of the total space. Air to fuel the fire is coming in from the bottom and top of the door. Positive pressure builds up forming a neutral pressure plane. This is the area between the positive pressure above the door and the neutral pressure below the door.

Five minutes into the fire, the fire is no longer confined to a small area. The smoke, pressure and heat fills the space at about 40 inches above the finished floor. Air is still coming into the room from under the door, but air is no longer coming in from the top of the door. The pressure has built up greatly, and with nowhere else to go, it has to escape through the gap at the top of the door between the door and frame.

In the old test, the neutral pressure plane was leveled off above the door, and none of the hardware was affected. With the new test, this neutral plane is lowered to 40 inches above the finished floor, and any hardware located above 40 inches is affected. And, while some of the pressure and smoke will go out a window or ceiling tile, most will go out the top of the door. This is why hardware located 40 inches above the finished floor is now more accurately affected by the new test.


Evaluation

Upon submission, results of your evaluation will be displayed with the correct answers shown in red.

  1. The Uniform Building Code (UBC) requires fire doors be tested under neutral pressure instead of positive pressure.
    True.

    False.


  2. With positive pressure testing, the neutral pressure plane is __________ .
    At the top of the door height.

    Lowered to a standard 40 inches above the finished floor.
    Measured from the ceiling
    .

  3. Regardless of door height, the neutral pressure axis is defined from the floor upward.
    True.

    False.

  4. The new UL 10C test method includes __________ :
    Hot air and gases are forced out at the top of the door.
    Ambient air is drawn in from under the door.
    No flame detected on non-fire side of door for more than 10 seconds.

    All of the above.

 

   
       
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