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Controlling smoke with doors and detectors:
In this issue, we will discuss smoke doors and the National Fire Alarm Code requirements for the application and placement of smoke detectors for the operation and control of the smoke doors. Generally, these devices are installed by the hardware contractor with the magnetic hold-open devices and smoke detection installed by the electrical contractor.
The smoke door requirements of NFPA 101-2006, Life Safety Code, is the example here, but I advise you to reference the locally adopted building code for every project.
Essentially, the requirements state that “A door normally required to be kept closed shall not be secured in the open position at any time and shall be self-closing or automatic-closing ... .” Smoke doors are “permitted to be automatic-closing, provided that the following criteria are met:
- Upon release of the hold-open mechanism, the door becomes self-closing
- The release device is designed so that the door instantly releases manually and, upon release, becomes self-closing, or the door can be readily closed
- The automatic releasing mechanism or medium is activated by the operation of approved smoke detectors installed in accordance with the requirements for smoke detectors for door release service in NFPA 72-2006, National Fire Alarm Code.
- Upon loss of power to the hold-open device, the hold-open mechanism is released and the door becomes self-closing.
- The release by means of smoke detection of one door in a stair enclosure results in closing all doors serving that stair.”
When detectors are used to prevent the spread of smoke by releasing smoke doors, there are differing requirements in the National Fire Alarm Code. The design could use area detectors installed in the smoke compartments or detectors located at each smoke door to release the magnetic hold-open device and allow the door to close.
Section 5.16.6 of NFPA 72-2006 covers the requirements for smoke detectors used for door release service. It states in part that “smoke detectors that are part of an open area protection system covering the room, corridor, or enclosed space on each side of the smoke door and that are located and spaced as required [by the National Fire Alarm Code] shall be permitted to accomplish smoke door release service.”
If the designer chooses to use smoke detectors exclusively for smoke door release, they must be located in accordance with section 5.16.6, which has specific rules based on the depth of the wall above the smoke doors. There are numerous figures in the National Fire Alarm Code to assist designers and contractors in the proper placement of smoke detectors to prevent smoke movement from one zone to another.
For example, if the depth of a wall section above the door is 24 inches or less, one ceiling-mounted smoke detector is required on one side of the doorway only, or two wall-mounted detectors are required, one on each side of the doorway. But if the depth of wall section above the door is greater than 24 inches on both sides, two ceiling-mounted or wall-mounted detectors are required, one on each side of the doorway.
Another example is when door release is intended to prevent smoke transmission from one space to another in one direction only, detectors located in the space to which smoke is to be confined, regardless of the depth of wall section above the door, must comply with Section 126.96.36.199.1, which states that “if ceiling-mounted smoke detectors are to be installed on a smooth ceiling for a single or double doorway, they shall be located as follows
- On the centerline of the doorway
- No more than 1.5m (5 ft) measured along the ceiling and perpendicular to the doorway
- No closer than [4 inches and no greater than 5 feet depending on the wall depth] as shown in Figure 188.8.131.52.1.1, parts B, D, and F”
Section 184.108.40.206 requires that “if ceiling-mounted detectors are to be installed in conditions other than those outlined in 220.127.116.11.1, an engineering evaluation shall be made.”
What should be obvious to the professional contractor is that the use of smoke doors for releasing service only has a great deal of special requirements regarding the placement of smoke detectors.
Ensure that corridor smoke detectors are installed in accordance with NFPA 72-2006, section 18.104.22.168.1 (referenced above) as this approach does not have to follow all of the special requirements of 22.214.171.124 and 126.96.36.199.
However, if you find yourself installing smoke detectors strictly for smoke door release (e.g., in a hospital or other healthcare facility) then a clear understanding of the requirements of section 188.8.131.52 and 184.108.40.206 is imperative. ECMOORE, a licensed fire protection engineer, frequent speaker and an expert in the life safety field, is a co-editor of the current National Fire Alarm Code Handbook. Moore is a principal with Hughes Associates Inc. and is located at the Warwick, R.I., office.