Printed from the blog of Lori Greene, AHC/CDC, CCPR, FDAI
Allegion
Email: lori_greene@allegion.com, Blog: www.idighardware.com or www.ihatehardware.com


Nov 18 2014

WWYD? Stairwell Pressure

I have been asked about this many times and I don’t have a good answer.  I’ve got my fingers crossed that someone reading this can help.  The issue is when you have a pressurized stairwell that is required for some buildings for smoke control.  With the increased pressure in the stairwell, doors swinging into the stair become more difficult to open, and doors swinging out of the stair may not close and latch.

For the outswinging doors that don’t close, the first thought is often to increase the closing force of the closer, but this increases the opening force as well.  For many jurisdictions, the maximum opening force for a fire door or exterior door is 15 pounds to release the latch, 30 pounds to set the door in motion, and 15 pounds to open the door fully (your jurisdiction’s requirements may vary).  What if that’s not enough force to get the door closed?

The next thought may be to add an automatic operator to assist with opening the door now that the opening force is so high.  There are two problems there – 1) low-energy automatic operators are limited by code to 15 pounds of opening force (that’s why they don’t need safety mats and guide rails) and 2) automatic operators on fire doors are required to be deactivated on fire alarm.  If you only have 15 pounds of opening force fighting an excessive amount of closing force, this doesn’t seem like it would help.  Going to a full powered operator that is not subject to the 15-pound limit would require safety sensors and possibly guide rails.  And during a fire alarm when the stair is pressurized, the auto operator is not functional if the door is fire rated.

When our specwriter apprentices are in Boston for training, I always take them on a field trip to a building where they can see some doors with this problem (and lots of other doors).  In this university classroom building, there are two outswinging pairs leading from the stairs to a lobby.  The doors have the closers that were originally specified and installed, added automatic operators with safety sensors both sides of the door, AND magnetic holders which hold the door open until the fire alarm is activated.  I have no idea if they actually get the job done – what is the purpose of the auto operators if the doors are held open when there is no alarm, and the operators are deactivated when there is an alarm?  If any of the apprentices reading this have some photos of these openings, send them along and I’ll post them.

Without knowing much about stairwell pressurization, it seems like there is too much pressure in the stairwell and it must be reduced.  But releasing too much air will mean that the pressure in the stairwell is less than what is required by code.  I didn’t do very well in physics and maybe that’s why I haven’t had a brainstorm on this.  I saw a nifty product called the Closer Pressure Equalizer a few years ago, but I haven’t seen it on the market.

So…what would you do? 

9 Responses to “WWYD? Stairwell Pressure”

  1. Sheldon says:

    How about a moratorium on code changes and new codes? Take the time to consolidate existing codes (didn’t we do that once?) and eliminate conflicts.

  2. Richard Leibowitz says:

    Not sure if this helps but…2009 IBC section 909.6.2 Maximum pressure difference (SMOKE CONTROL SYSTEMS)…The maximum air pressure difference across a smoke barrier shall be determined by required door-opening or closing pressure. The actual force required to open exit doors when the system in smoke control mode shall be in accordance with 1008.1.2 See equation 9-1

  3. Paul Goldense says:

    Lori Without knowing about the design of the smoke evacuation system of the building it is hard to be sure, but you cannot rule out that the auto operators are there to open the closed doors for makeup air on the smoke evac system. While this flies in the face of the fact that the stair Fire door is supposed to be closed and latched crazier things have been done in design.

    Many times when the smoke evac system is running it will suck the doors shut so it is posibile that the magnets are there to hold the doors in the open position and in fact do not release on Fire Alarm.

    The Sensors on the operator may be because the operator is not low energy and in fact high energy and needed to open the doors against the smoke evac fan suction.

    I have had to use 600# maglocks mounted to walls to hold doors open for smoke evac because the “Blow Open” smoke operators in fact broke down trying to hold the doors open against the fan suction.

    • Lori says:

      Thanks Paul. Harris was involved with this one so I know that the doors were not part of a blow open system. It was a series of band-aids to try to make it all work. 🙁

  4. Jess says:

    this question sounds like a few of the recent questions I have received, one from a nuclear power plant in Ohio and one from a door installer in Calif.

    the solutions I suggested to the Nuclear power plant (about 6 or 7 different ideas) some involved the closers themselves, (2 ways of using 2 units on the door to get the most out of the strength of them)

    other options included lowering the pressure of the HVAC system, using spring hinges to assist the closers, repositioning the closer or it’s arm shoe for more strength if adjusting the spring was not of any help.

    the most “invasive” involved using a helical coil torsion spring based closer (potbelly closer) or if don’t want to see it, use of a Rixson floor closer (#27/#28 or 30/40 series)

    re-hanging the door may help, but if above the ADA codes compliance it may be best to work with the HVAC mechanic to work on lowering the blower pressure in the building,

    -Jess the door closer doctor

  5. Max says:

    I run across this issue, to varying degrees, on almost all of my stair press special inspections projects in Boston. Now try making it work on a residential high-rise in California, where CBC §1126A.4 is typically interpreted as reducing the maximum allowable force to set the door in motion to 15-lbf.

    The first step is to play with the architectural design/construction quality. For an interior outswinging door (i.e. stair discharging through a vestibule or lobby), a tighter lobby will result in less air flow through the door opening and the door therefore has lower air velocities to overcome in order to latch.

    When that fails or is infeasible: the first step is to adjust the latching speed. The last few inches of travel are the issue and a little extra momentum here goes a long way. There is not a lot of room for adjustment before the door becomes non-compliant when the fans are NOT running.

    Next, the go-to is typically to add a second closer. This quickly results in a non-compliant door. Opening force is fine with the fans running, but greatly exceeded with the fans off. Additionally, this typically results in a door that closes too fast with the fans off.

    The last-ditch effort is to provide a powered closer. On an un-rated exterior door this is typically acceptable as long as it is provided with backup power. On a rated door, there may be an opportunity to secure AHJ approval as an alternate means or judgment.

    I don’t know that anyone has found a good solution.

  6. Domenic LoBello says:

    Lori the purpose of stairwell pressurization is to keep smoke out of the stairwell even if a door is left open.
    If properly designed, the positive air pressure in the stairwell will keep the smoke from entering, keeping the pathway clear of smoke for evacuation.
    Any additional attempts to add power operated hardware or maglocks would hamper egress

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