Fire and life safety design trends fuel innovation
Fire and life safety innovations arise from current design trends in tall buildings. In response to these trends, a number of fire and life safety innovations have been developed.
The Council on Tall Buildings and Urban Habitat defines a high-rise building as “a building whose height creates different conditions in the design, construction, and use than those that exist in common buildings of a certain region and period.” This definition, although lacking in a certain precision found in conventional building code definitions, successfully highlights the principal challenges that face designers as they seek to develop a building typology that simultaneously allows for operational and programmatic efficiencies, while not in any way compromising the life safety of the occupants therein. In contrast with this goal, however, the “June 2009 National Fire Protection Association Report on High-Rise Fires” indicates that in the United States alone, more than 13,000 fires have occurred each year in high-rise buildings resulting in more than 60 civilian deaths and approximately $180 million in damages1. This report also notes that the risks of fire, fire death, and direct property damage due to fire tend to be lower in high-rise buildings than in other buildings of the same property use. While far from an abysmal record of accomplishment, the continued challenges to fire and life safety warrant a closer look in the context of current design trends and the corresponding innovations intended to address occupant life safety and property protection.
The past two decades have been characterized by a confluence of renewed interest in urban density, significant advancements in sustainable design practices, and exponential improvements in information technology. These factors, coupled with the continued evolution of structural engineering, improved facades, high-performance building environmental systems, and more robust fire and life safety systems have influenced skylines in cities all around the world in exciting and sometimes daunting ways.
More than just structures for commerce and shelter, tall buildings have continued to both define and reflect economic and societal values, pushing the boundaries of design on the path toward becoming iconic symbols of our technological age. Three design trends that have emerged in this framework include:
- Development of ever-taller buildings with more diverse uses and higher densities.
- Integration of sustainable principals into all aspects of tall building design, inclusive of environmental and smoke management building systems.
- Increased focus on providing real-time information to building occupants during both emergency and non-emergency conditions.
In response to these trends, a number of fire and life safety innovations have been developed. This article explores these innovations, including the benefits and potential pitfalls of these trends, which include:
- Enhanced elevator evacuation systems designed to get people out of the building faster
- Natural ventilation smoke management systems intended to complement firefighter efforts to manage the impacts of smoke and heat
- Mass notification systems (MNS) designed to communicate critical information more efficiently with greater precision.
Design Trend #1: Design of increasingly taller buildings to achieve more diverse uses and higher densities
Innovation: Emergency elevator evacuation systems (EEES) to serve building occupants and firefighters
Recent editions of the International Building Code and the NFPA Building Construction and Safety Code (NFPA 5000) have included increasingly defined requirements for enhanced- occupant evacuation elevator systems. Although not yet a widely applied component in the overall fire and life safety package provided for tall buildings in the United States, the use of EEES in other countries has been more commonplace. Regardless of the country or code basis, such systems have conventionally shared a few key components, including:
- Protected lobby to provide a staging area that can also serve as an area of refuge
- Drainage safeguards near elevator doors to minimize water leakage into shafts
- Pressurized elevator shafts or lobbies to limit the potential for smoke entry into shafts
- Audio visual communications systems in the elevators and refuge areas so that conditions and occupant status can be assessed
- Enhanced controls to operate the elevator (for firefighters)
- Robust elevator car doors that can operate under a variety of pressure/friction conditions
- Enhanced power supplies for primary and secondary equipment including motors and air conditioning, respectively.
In consideration of the potential benefits to both building occupants and firefighters alike, it is useful to look at the merits and potential challenges associated with this innovation.
Benefits of enhanced elevator evacuation systems
Conventional occupant evacuation in tall buildings having more than 40 stories may take hours, depending on the modes of occupant notification and the specific characteristics of the building occupants. Studies have shown that the use of stairs alone in tall buildings yields egress times that are twice that required when stairs and enhanced evacuation elevators are used together2. Apart from providing an increased evacuation capacity, such approaches permit disabled, elderly, and very young occupants from using the elevator during an emergency in lieu of the stairs, thereby reducing the likelihood that the flow of occupants within the stair enclosures will be hindered.
Implementation of EEES can also provide significant benefits for firefighters undertaking search and rescue, suppressing a fire, or conducting overhaul operations after a fire has been extinguished. For example, scenarios involve firefighters trying to get up the stairs while occupants are trying to go down, such as was experienced at the World Trade Center in New York. These situations could be largely mitigated such that firefighters could have nearly unimpeded access to upper floors without significantly reducing the occupant evacuation capacity. Further, the use of stairs only in tall buildings poses logistical challenges in connection with the weight and quantity of equipment that must be transported to a fire. In the absence of safe and reliable vertical transportation systems, firefighters must use the building stairs, potentially using up oxygen supplies and wasting valuable time in an effort to reach the next staging location. For those fire departments that have made it their practice to use elevators during the course of manual suppression and overhaul activities, the enhancements provided by EEES represent a significant improvement in the level of safety over that provided by conventional elevator systems. Frequently, traditional elevator systems lack the many enhancements designed to resist the effects of smoke, heat, and water on the vertical transportation system.
Caveats for enhanced elevator evacuation systems
Whereas enhanced elevator evacuation systems are fundamentally more complex than stair enclosures, it is critical to take note of past failings when implementing these types of systems. Practical considerations borne of experience include the following:
- People must accept the system. Training and signage are an integral part of achieving adequate comfort levels with elevator systems, especially given the historical stigma associated with using elevators during fire emergencies in places such as the United States.
- Operators of controls systems for elevator evacuation need to be well trained not only to know the most effective way to effect an elevator evacuation, but also to be able to respond to potentially hazardous conditions or circumstances.
- People in the elevators as well as the system itself must be protected from heat, smoke, water, etc.
- System components must be reliable. Water-resistant equipment is needed and power supplies must be robust.
- Elevator evacuation controls must be provided in the elevator car so that elevator doors and car movements can be controlled to a greater extent (e.g., relying on automatic systems may not always be appropriate).
- Communications between the fire command center and elevator lobbies and/or the elevator cars themselves (e.g., from telephones, intercoms, call buttons, detectors, water flow, etc.) must be available and easy to use so that occupants who are waiting for the elevator can be informed as to the status of the elevator, as well as other evacuation options.
- Discharge lobbies and floors must be able to handle the flow of people so that the likelihood of overcrowding at the elevators themselves is minimized. Additionally, adequate compartmentalization at elevator lobbies and related refuge areas must be provided.
Design Trend #2: Use of natural ventilation to enhance the building environment in highly sustainable tall buildings
Innovation: Natural ventilation smoke clearance systems to facilitate manual suppression activities
In contrast with the industry’s embrace of natural ventilation systems in buildings less than six stories, the introduction of mixed mode systems (natural and mechanical) in tall buildings has been slower in part because of the inherent complexity and added costs of hybrid systems, and in part due to the perception of increased risks to building occupants and the structure. Nonetheless, the continued drive to reduce operational costs and increase the sense of well-being for building occupants has translated into a strong desire to integrate fresh air approaches in tall buildings that have traditionally been isolated from external environmental forces.
In response to the hermetically designed spaces that have dominated tall building construction in the past couple of decades, smoke management strategies have been tailored to take advantage of a system of pressurized or depressurized compartments that limit the spread of smoke and fire. Key components of such systems include:
- Stair pressurization with or without vestibules
- Elevator shaft pressurization or pressurization of corresponding lobbies
- On-floor pressurization or depressurization to prevent smoke migration from the floor of origin.
Although these systems can effectively limit smoke spread or contain products of combustion to the zone of origin, they do not generally contribute to the tenability on the fire floor itself, which would be expected to degrade over time. As such, conventional pressurization without air changes on the fire floor does not confer any particular advantage to building occupants or firefighters undertaking search-and-rescue or manual suppression activities in the zone of origin.
Benefits of natural ventilation smoke clearance systems
In combination with automatic fire suppression, natural ventilation via louvers or similar dedicated venting systems can enhance existing smoke containment (i.e., pressurization) by introducing an air change component that removes smoke and heat during the fire. Alternatively, if a particular system configuration does not permit smoke clearance in conjunction with pressurization during the fire, the use of pre-existing natural ventilation infrastructure after the fire has been controlled can greatly simplify overhaul operations by more quickly allowing for smoke to be cleared without having to break out windows or use supplemental fan systems. Whereas traditional pressurization systems are not specifically designed to clear smoke, the integration of natural ventilation components provided for normal building ventilation can provide significant smoke clearance benefits with minimal additional cost if considered at the onset of a project. Practically speaking, such systems can come in very handy for the more common small fires (e.g., a fire in a kitchenette on an office floor), even if they are never put into service in connection with a more severe fire.
Caveats for implementing natural ventilation smoke clearance systems
Natural ventilation may not be the right approach for a particular building depending upon its location and relationship with the environment around it. This is especially true for tall buildings. Often, the very forces that are harnessed to achieve natural ventilation of spaces in tall buildings are the same forces that can contribute to a rapid fire spread. For example, while wind-borne air movement can create desirable cross-flows that can keep a work space cool under normal conditions, such phenomena could also result in an intense uncontrolled fire under adverse circumstances1. An important consideration, therefore, is how to manage wind-induced flows, buoyancy-induced flows, and stack effect during fire conditions3.
- Although it may be beneficial to take advantage of a small breeze via operable windows, the presence of such openings could create very large fire problems as wind pressures increase as a function of building height. Such challenges would be diminished in buildings where no openings were present, thus reducing the possibility that wind could agitate a fire to the point that it is not even possible to approach it from the zone (floor) of origin. At the very least, consideration of how openings can be controlled and how a fire could be suppressed if those openings were not able to be controlled is needed.
- Stack effect plays an important role in convection ventilation schemes such as those found with double-skin facades. However, the very same ventilated facades that allow for movement of air up or down the height of the building can also contribute to fire spread if care is not given to controlling potential fires or limiting the impacts of fire in such building elements.
- The principal concern related to buoyancy is that it could be adversely impacted by sprinkler operation, which would subsequently result in a cooling of heated gases. Such cooling could cause the smoke to go into places where it is unwanted.
In the excitement of developing sustainable design approaches, full consideration must be given to the ways that the driving forces for natural ventilation can be exaggerated as a result of the building height, or presence of a fire.
Design Trend #3: Enhanced information management and communications
Innovation: Use of MNS to achieve enhanced occupant notification
MNS have been around for a very long time. We may remember the town siren being tested every evening in the summer. If it operated during other times, we knew it was a warning of hazardous weather or tornadoes. The advent of terrorist events like Khobar Towers bombing in Saudi Arabia in 1996, drove the development of MNS for buildings. Over the course of the last seven years, the technical committees responsible for NFPA 72: National Fire Alarm and Signaling Code have worked to incorporate criteria in the code to address the design and installation of standalone MNS as well as providing criteria to allow fire alarm systems to serve a dual purpose: fire alarm and mass notification.
Benefits of MNS
Mass notification systems can be used to provide timely information to occupants of a building that could be crucial to their safety. The system can be manual or automatic and may provide instruction for a wide variety of situations. These may include various emergencies including:
- Security (presence of armed assailants, etc.)
- Health (toxic release)
- Geological (earthquake, volcano, tsunami, etc.)
- Meteorological (tornado, hurricane, flood, hail, etc.)
- Terrorism related.
Emergency communication by way of a MNS can take precedence over a fire alarm depending on the circumstance. There may be instances when even though the fire alarm system is broadcasting an evacuation signal, it may be more appropriate that occupants take alternative action. Manual override can be executed to communicate alternative instruction. The arrangement and operating procedures for mass notification should be developed based on a risk assessment and be consistent with other emergency plans for a building.
Caveats of MNS
It is imperative that MNS be secure and available only to trained, qualified personnel to minimize the probability of inappropriate messages being transmitted. The scenarios under which a system would be used need to be evaluated. Clear and direct operating procedures for the use of the system need to be developed, and operators need to receive appropriate training.
Current design trends in tall building design are influencing how fire and life safety is approached in any number of building typologies. The desire to create ever-taller buildings to achieve more diverse use and greater density, the need for more sustainable structures, and an overriding mandate to manage information and communications in a more robust manner have given rise to several key fire and life safety innovations. In particular, the implementation of MNS, the introduction of EEES, and a renewed interest in natural smoke ventilation approaches in tall buildings have generated a great deal of excitement due to the potentially significant benefits to fire and life safety. In the midst of these new possibilities, however, designers are cautioned to consider any number of factors when determining whether a particular solution is appropriate for a given project.
– Grill is a principal with Arup, where he focuses on fire protection engineering. He is a member of Consulting-Specifying Engineer’s editorial advisory board and a past president of the Society of Fire Protection Engineers. Wittasek is an associate principal with Arup where he focuses on fire protection engineering.
1Hall, John R. Jr., High-Rise Building Fires, published by the National Fire Protection Association, NFPA No. USS30, June 2009.
2Wong, Kelvin, M.C. Hui, D.G. Guo, and M.C. Luo, A Refined Concept on Emergency Evacuation by Lifts, Fire Safety Science 8: 599-610. Doi: 10.380/IAFSS.FSS.8-599.
3C.L. Chow and Koen Steemers, “Possible conflicts on smoke controls in buildings with national ventilation,” Paper No. 33, Department of Architecture, the Martin Centre for Architectural and Urban Studies, University of Cambridge, 6 Chaucer Road, Cambridge CB2 2EB, UK.