When a fire alarm system is activated and many of the occupants do not leave, is that bad or good? In most cases, the system design is intended to initiate evacuation. So when people ignore or choose to not leave, the fire safety objectives have been compromised. However, there are circumstances where the fire safety objectives include provisions for partial evacuation or relocation of the occupants away from the immediate fire or smoke zone. There are also situations where only those persons in the most immediate area of the fire need to be moved. All others Stay In Place, while passive, active, automatic and manual fire protection systems are used to Defend In Place.
Figures 1 and 2 show part of the Fire Safety Concepts Tree from NFPA 550.1 The Fire Safety Concepts Tree is an event tree using logical "AND" gates (multiplication symbol) and "OR" gates (addition symbol) to relate various combinations of subevents that lead to the top level successful event. An "AND" gate indicates that all events immediately below that event must occur for the event to be a success. For an "AND" gate, the probability of success is determined by multiplying the probabilities of the lower events. For an "OR" gate, the probability of success is determined by adding the probabilities of the lower events.
The most common application of a SIP & DIP strategy is in healthcare occupancies. Where patients are not ambulatory or where their movement is restricted, limited or slow, building and fire codes have evolved to a SIP & DIP strategy. To be successful, those in immediate danger are moved to a safe area. The safe area is defended with some combination of fire and smoke barriers, smoke control or smoke management, and active and/or manual fire suppression. Staff training and fire safety planning are an integral part of the SIP & DIP strategy.
A 1989 paper2 reviewed and analyzed fires in hotels, motels, apartments, condominiums, dormitories, residential board and care facilities, hospitals and other healthcare occupancies. The paper has three main conclusions:
- If the fire is in an occupant's room or unit, they should leave. If not, they should stay in place.
- Evacuation of the fire floor in the occupancies studied increased the probability of death.
- Self-closers for doors in the egress path are a critical element for a SIP & DIP strategy.
It should be noted that many of the fires where occupants did not evacuate and did survive occurred in nonsprinklered buildings. In those cases, passive containment by fire barrier systems, and in some cases smoke barrier systems, was an important factor for success. In all cases, success requires a combination of fire safety features or systems. Also, almost all of the injuries and deaths occurred in places where evacuation time was large compared to fire development time. The common characteristic among all of these occupancies is that they are highly compartmented and fire-resistive.
Life safety, building and fire codes contain and require the features for a successful SIP & DIP strategy in healthcare and high-rise multiunit residential occupancies. The codes have stringent requirements for corridor fire separations and for separations between residential units. These separation requirements include self-closing doors. Flame spread and smoke development limits for interior finishes used in egress components help maintain a safe environment for partial relocation.
In Figure 2, the event "Cause Movement of Exposed" requires that the need be detected and signaled, and that instructions be provided to the intended occupants. These same three subevents can be placed under the "Restrict Movement of Exposed" event that is a part of the "Defend Exposed In Place" branch of the tree. In healthcare occupancies, these events are managed with automatic and manual fire detection, voice communication systems and staff training. However, in residential occupancies, these three components are not typically optimized for a SIP & DIP strategy.
For residential occupancies, the difficult-to-evacuate situation occurs in highrise buildings. The model codes all require some combination of automatic fire detection and/or automatic suppression to meet the "Detect Need" event. However, the "Signal Need" and "Provide Instructions" events are typically not optimized for SIP & DIP. Most high-rise buildings have or require an emergency voice alarm communication (EVAC) system. Because the system is intended to be used for an extended period during fire emergencies even where a SIP & DIP strategy is not a part of the fire safety plan, the National Fire Alarm Code3 requires that the system be designed and installed with certain survivability features. However, those minimum requirements do not address survivability of circuits and components within the compartment of fire origin. Thus, they are not optimized for a true SIP & DIP strategy.
Instructions are provided to occupants and staff in two ways. In most situations, prefire training is the most prevalent mechanism for providing instructions. The second method uses communication systems during the emergency. In healthcare, voice systems are typically used to provide specific event and location information to the staff. However, in residential occupancies where an EVAC system is required, a prerecorded voice message provides standard instructions that often fail to provide instructions suitable for SIP & DIP. An example is the following message that is required in one state for all EVAC systems:4
"Attention, please. The signal tone you have just heard indicated a report of an emergency in this building. If your floor evacuation signal sounds after this message, walk to the nearest stairway and leave the floor. While the report is being verified, occupants on other floors should await further instructions."
Obviously that message is not intended for a SIP & DIP strategy. However, it also fails in both format and content of critical information and directions to the occupants.5 Some information and instructions could be provided to residential occupants before a fire or other emergency. In addition, the fire alarm system can be used to provide live voice instructions once the fire department is on-scene. A prerecorded message could be used where professionally trained staff are not in place until the fire department arrives. The message might be similar to the following:
"A fire emergency has been reported. The fire department is responding. For your safety, stay in your apartment and await further instructions. If the fire is in your apartment, leave immediately" [Repeat].
Systems could also be designed to include specific fire-floor information in the message.
Almost all fire alarm systems include both audible and visible systems for occupant notification. However, the visual part of the occupant notification system is almost always composed of strobe lights. In systems that use voice as the audible occupant notification system, the use of strobes for visual signal fails to provide an equivalent visible system. Strobes are single-bit notification appliances. They cannot provide a stream of information equivalent to a voice communication system.
In a 1970 fire at a Chicago hotel, most occupants of the ninth floor where the fire originated survived as they were directed by firefighters to remain in their rooms with the doors closed.6 Two hard-of-hearing individuals died when they attempted to evacuate.
Visual signaling is not only for the hearing-impaired. Confidence is increased when information and directions come from multiple sources. For a SIP & DIP strategy to be successful, fire protection engineers must provide systems that reliably communicate to all occupants and staff using multiple delivery formats. To be reliable, the systems must have a high statistical availability7 and users must be familiar with them.8 The higher degree of statistical availability is achieved, in part, through the design and installation of systems that have a higher degree of survivability or that use redundant delivery systems, components or formats. Where a SIP & DIP strategy includes keeping people in place on the same floor as the fire origin and providing them with directions and information, the system must have survivability features that go beyond current requirements listed in the National Fire Alarm Code.
SIP & DIP is a strategy already practiced by many fire departments for fires in large residential occupancies as well as healthcare facilities. A SIP & DIP strategy must be a planned with critical infrastructure elements that differ from conventional evacuation systems. To meet the needs of the occupants and staff, fire protection engineers need to be involved in the planning and implementation of all systems used by the strategy. NFPA 550 provides a framework for planners and designers to ensure that all required features are considered passive and active, manual and automatic. It also provides a simple way to communicate the strategy. As the needs of society evolve to require better and more sophisticated communication strategies during a variety of emergencies,9 properly planned and implemented SIP & DIP strategies can be used to increase overall effectiveness and save many lives.
1 NFPA 550, Guide to the Fire Safety Concepts Tree, 2007 edition, National Fire Protection Association, Quincy, MA.
2 Macdonald, James N., Non-Evacuation in Compartmented Fire-Resistive Buildings Can Save Lives and It Makes Sense, Travelers Insurance Co., Hartford, CT, July 1989.
3 NFPA 72, National Fire Alarm Code, National Fire Protection Association, Quincy, MA, 2006.
4 Massachusetts State Building Code, Sixth Edition, 1997.
5 "Messaging and Communication Strategies for Fire Alarm Systems," Fire Protection Engineering, Summer 2003, pp. 50-53.
6 Grimes, M.E., "Hotel Fire Chicago," Fire Journal, National Fire Protection Association, Quincy, MA, May 1970.
7 "Mission Effectiveness and Failure Rates Drive Inspection, Testing and Maintenance of Fire Detection, Alarm and Signaling Systems," Fire Protection Engineering, Summer 2002, pp. 25-27.
8 "Combining Emergency Voice and Non-Emergency Paging Systems," Fire Protection Engineering, Spring 2004, pp. 48-51.
9 "Mass Notification Systems," Fire Protection Engineering, Fall 2005, pp. 58-60.
Editor's Note About This Article
This is a continuing series of articles that is supported by the National Electrical Manufacturer's Association (NEMA), Signaling Protection and Communications Section, and is intended to provide fire alarm industry-related information to members of the fire protection engineering profession.
* Reprinted with permission from NFPA 550-2002, Fire Safety Concepts Tree, Copyright 2002, National Fire Protection Asociation, Quincy, MA 02269. This reprinted material is not the complete and official position of the NFPA on the referenced subject, which is represented only by the standard in its entirety.