Thursday, May 16, 2013

Smoke Detector Placement for Magnetic Door Holders

What are Magnetic Door Holders for Fire Walls


Fire rated doors are in place to control the spread of fire through corridors and passageways.  In a perfect world, these doors would be kept closed at all times.  However, facilities typically want more of an open floor concept as well as ease of access for their visitors.  This is where electromagnetic door holders came into play.  These fire rated door holders have an energized coil which creates a magnet strong enough to hold the self closing fire rated doors in the open position.   On the fire alarm side, you would need a control relay to intercept a switch-leg of power to the door holder circuit as well as an initiating device such as a smoke detector to activate the relay.  Once the detector senses smoke, the fire alarm control unit sends a signal to the relay which then opens the power circuit.  Once power has been lost to the door holders, the coil is de-energized and the magnet no longer has the pulling force to hold the door in the open position.  The self closing mechanism shall close the door from a fully open position (90 degrees) to 12 degrees from the latch at a minimum of 5 seconds.  This insures the doors do not close to quickly.  This information can be located in ANSI 117.1 2009 section 404.2.7.1.


Smoke Detector Placement for Fire Rated Doors and Magnetic Door Holders


There are a few things to keep in mind when installing smoke detectors for magnetic door holder releasing.  For this information we must consult the standards found in NFPA 72 2013.  Below we have broken down a few code sections from chapter 17 to help clear up any confusion:

NFPA 72 2013 SD Spacing Requirements:    


17.7.5.6.5.1 (A)
If the depth of the wall section above the door is 24 inches (610 mm) or less, one ceiling mounted smoke detector shall be required on one side of the doorway only, or two wall mounted smoke detectors shall be required, one on each side of the doorway.

17.7.5.6.5.1 (B)
If the depth of the wall section above the door is greater than 24 inches (610 mm) on one side only, one ceiling mounted smoke detector shall be required on the higher side of the doorway only, or two wall mounted smoke detectors shall be required, one on each side of the doorway.

17.7.5.6.5.1 (C)
If the depth of the wall section above the door is greater than 24 inches (610 mm) on both sides, two ceiling mounted smoke detectors or two wall mounted smoke detectors shall be required.  One on each side of the doorway.

Fire Alarms Online note:  Per Figure 17.7.5.6.5.1 (A) in NFPA 72 2013, the smoke detectors used for the purpose of releasing magnetic door holders shall be located within 5 feet of the header.


Smoke Detectors Placement for Door Holders
Smoke Detector Within 5 Feet of the Header
In the above picture, you can clearly see that the header or space above the doorway with magnetic door holders is less than 24 inches (610 mm).  However, the installing fire life safety company installed a smoke detector on the ceiling on both sides of the doorway.  This smoke detector placement is not required but it never hurts to have extra coverage.  Just thought I would point it out.
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