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Space at the bottom of a Fire Door

Discussion in 'Commercial Fire Codes' started by RJJ, Aug 8, 2018.

  1. RJJ

    RJJ Platinum Member

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    Just wondering what you all would allow for the space located at the bottom of a fire door? Like to hear some feed back and why!
     
  2. RLGA

    RLGA Sawhorse

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    What do you mean by "space"? Are you referring to the gap between the floor surface and the bottom of the door?
     
  3. ADAguy

    ADAguy Sawhorse

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    That is what he is alluding too, at what dimension is the gap too big to affect the fire rating?
    Or, can the door swing over dissimilar flooring materials, carpet to vct without a threshold?
     
  4. RJJ

    RJJ Platinum Member

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    The space / gap between the floor and the bottom of the door?
     
  5. RLGA

    RLGA Sawhorse

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    NFPA 80 states 3/4-inch maximum, unless the door assembly has been tested with a gap greater than 3/4-inch.
     
  6. cda

    cda Sawhorse

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    I take it the gap is only in play ...

    When the door is closed
     
  7. Paul Sweet

    Paul Sweet Sawhorse

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    The bottom of the door is at negative pressure during a fire, so air will be pulled in rather than flames & smoke escaping.
     
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  8. cda

    cda Sawhorse

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    That’s not how it was in Backdraft??

    I am thinking pressure may depend on the stage of the fire???
     
  9. RLGA

    RLGA Sawhorse

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    As a fire burns and heat rises, it draws combustion air from the lower levels, and door bottom clearances is an area where that air is drawn through. As the air is sucked through the bottom of the door in puts an inward pressure on the door (inward toward the fire). Hot air and gases build up in the upper portion of the space creating an outward pressure on the upper surface of the door. These two forces will attempt to warp the door. This is why fire doors are tested with a neutral plane at 40 inches above the floor per UL10C and NFPA 252.

    If smoke begins to be drawn back through gaps at the upper portion of the door, then the fire is starving for oxygen and hot combustible gases begin to build up inside the space (i.e., backdraft). If oxygen is suddenly introduced into the space (e.g., a window breaks), then the hot combustible gases may rapidly re-ignite (explosive-like) similar to a properly balanced fuel/air mixture.
     
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  10. cda

    cda Sawhorse

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    Thank you

    Late in the evening to think about fire dynamics
     
  11. steveray

    steveray Sawhorse

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    3/4" is what I remembered, but never had a copy of NFPA 80...Thanks Ron!
     
  12. RJJ

    RJJ Platinum Member

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    Yes thanks! I have a hard copy of NFPA 80 buried some place. Sometimes finding stuff I save is like looking for Jimmy Hoffa! 3/4 is what I remembered. Just ran across 6 doors that have been installed @ 11/4" off the floor. That is why I raised the question.
     
  13. cda

    cda Sawhorse

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  14. cda

    cda Sawhorse

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