Tips to design multifamily and mixed-use buildings: Fire, life safety
- Brian Berg, PE, LEED AP, CEM, Associate Principal, Glumac, Irvine, Calif.
- David Crutchfield, PE, Principal, RMF Engineering, Charleston, S.C.
- Kieran Healy, PE, Mechanical Engineer, CCJM, Chicago
- Lui Tai, PE, Technical Services Director, JENSEN HUGHES, Toronto
- Robert J. Voth, Executive Vice President, Bala Consulting Engineers, King of Prussia, Pa.
CSE: What are some of the challenges for fire and life safety system design for multifamily dwellings and mixed-use buildings? How have you overcome these challenges?
Tai: The conflicting requirements of life safety versus security always pose an interesting challenge. In a fire scenario, all doors must be released to allow for safe egress from the building, yet in some secured areas, keeping the doors secure is almost equally important to stop patients from wandering off in case of a nuisance alarm. We often introduce a small time delay into the release of a secured door, which would allow staff members of a nursing home to confirm the fire condition and then be present at this unsecured door to attend to the needs of those in evacuation.
Berg: Space is always tight and valuable for high-rise multifamily buildings, so it’s often a challenge squeezing in smoke exhaust and smoke-exhaust make-up air shafts. We’ll often use a make-up air shaft for double-duty and provide space conditioning during normal operation through the same shaft.
CSE: Describe unique security and access-control systems you have specified in such facilities.
Tai: For secured floors, magnetic locks are often used on exit doors to control access and exit from the secured floor area. However, the code requires that all doors equipped with magnetic locks be equipped with a manual pull station, which would release the door in case of a fire to allow safe egress from the floor area. To prevent the misuse of the manual station to release the door, the manual stations are specified with audible covers, which produce a high-pitched sound when a cover is opened to gain access to the manual station. This is used to alert staff and deter the misuse.
CSE: Do you see any future changes/requests to building design in regard to fire/life safety systems, specifically in nursing homes?
Tai: Because of the trend toward a common platform for building systems, we will likely see the convergence of various building systems made by one system manufacturer. This would include the fire alarm system, nurse-call system, access-control system, CCTV, and voice-communications paging system. The other trend is to have wireless technology and mobile devices incorporated into the systems, such as the nurse-call system and the communications system.
CSE: Describe the cost and complexity of fire protection systems involved with such structures. Have they changed over the years?
Voth: Fire protection systems have dramatically changed when structures exceed 340 ft in height. Current techniques include a spare high-zone fire pump and secondary-water street service. Depending on the regional AHJ, storage tanks for fire protection systems may be required at the top of the building.
Tai: The cost of the intelligent control systems for the multifamily dwelling and mixed-use building has gone up because of the sophisticated computing power of the control panels. However, hardware cost for field wiring is reduced due to the programmability of the system components. Overall, the cost of the fire protection system is only increased marginally over the years. The noticeable increase in cost comes from the requirement that all sleeping rooms must be equipped with visual signaling devices.
CSE: In supertall, high-rise multifamily dwellings and mixed-use buildings, what types of areas of refuge, elevator egress, or other solutions have you implemented?
Tai: In a typical high-rise building, smoke detectors are designed into every elevator lobby to allow elevators to return home on any fire condition. The smoke detector installed on the home floor will send the elevators to their alternative home floor. In a supertall, high-rise building, occupants cannot use the stairs to exit the facility, thus must use the “egress elevators.” Designated egress elevators are installed in a 4-hour-rated shaft, with designated stops (i.e., every 10 or 15 stories) along the way, which are constructed as fire-rated and pressurized spaces. The elevator call button in these designated stops are connected to the smoke detector in the corresponding elevator lobby, which would stop the egress elevator from stopping on this floor should the smoke detector be activated.
Voth: We are engineering dedicated firefighter wireless communication systems in all of our supertall structures; egress stairways are now sufficient to let firefighters into the building while providing an egress path for occupants.
CSE: In extremely large complexes, what unique smoke-control or fire suppression systems have you specified? Please describe.
Tai: For extremely large complex facilities, quite often with build-in interconnected floors (i.e., airports, shopping centers), smoke control is one of the most important aspects of life safety design. Depending on the shape and dimension of the interconnected floor space, smoke control must sometimes be divided into smaller quadrants or areas, to allow smoke to be extracted locally before spreading to other areas in the open, interconnected space.