Consulting-Specifying Engineer - September 2008 - (Page 26)

Simultaneous evacuation Traditional approach for a broad range of building types and uses; may be required for buildings designed for extreme events. Critical features For typical structures, all that is required is a reliable means of notification. For tall or iconic buildings using simultaneous evacuation to address extreme events, care must be taken to review exit widths, along with the overall life safety, as prescribed code may not be adequate. occupants can safely exit under the design scenarios is necessary. Performance-based approaches rely upon state-of-the-art knowledge of human behavior and movement during emergency incidents. John Klote, in his article “Smoke Control and Fire Evacuation” published in Heating/Plumbing/Air Conditioning Engineering, gives an overview of evacuation calculations (Klote, 2008). This topic is covered in more detail in “Egress Design Solutions: A Guide to Evacuation and Crowd Management Planning.” Selecting options The selection of an appropriate egress strategy requires a good understanding of the building and its occupants, the protection measures in place, and the expected emergency response. Strategy selection also hinges upon the possible emergency scenarios. It also is important to consider the messaging strategy. The strategy needs to match the ability, activity, and responsiveness of the occupants, as well as the staff’s ability to assist in the process. Other considerations include the number of people who will need to evacuate, whether all occupants within the facility will be exposed to hazardous conditions, the occupants’ familiarity with the exits and egress routes, whether reliable staff will be available during an emergency, and what events will be considered. The answers to these questions provide critical information needed to select the strategy. Coordination of safety features is critical to the success of the egress strategy during an event. For complex facilities, it is often necessary to develop an overall fire and life safety strategy to coordinate these features. Voice communication, suppression, and detection system zones need to match with the evacuation zones. Emergency lighting is necessary in exit pathways to allow safe movement. Exiting components will likely require appropriate fire ratings. In some cases, additional voice communication zones, two-way communication, message boards, or other communications systems may be necessary to provide occupants with an appropriate situational awareness and a general understanding of the incident. Figure 3 The simultaneous full building evacuation strategy has emerged as an alternative solution for large, tall, or iconic facilities, particularly when designing for extreme events. Source: Arup recent code advancements, will likely lead to greater acceptance of these systems. Ultimately, it appears that codes will evolve to allow protected elevators as part of typical tall building design. Until that time, engineers must use performance-based approaches to implement evacuation elevators. Event-based evacuation With event-based evacuation, conditions dictate the specific actions and egress strategy. Situations are assessed and a decision is made based on that assessment to determine which strategy is appropriate. For example, consider a fire event on a single floor—relocating and protecting in place might be appropriate for this event. For the same building, a severe wind event may require full building relocation to an underground parking floor. For a wind event, elevators may be appropriate. This event-based strategy is especially useful for facilities that may be exposed to a range of events, particularly when those events can take place both inside and outside of the building. Events occurring outside the building may require a very different response than those occurring inside. This strategy places a large burden on the decision makers and the decision-making process. Decision makers need relevant information and the authority to make critical decisions. Flexibility can be a benefit. However, simplicity breeds reliability. Substantial prior training is required to minimize confusion when event-based strategies are in place. It is imperative to create appropriate systems and methods for quickly obtaining credible information about the event and to empower decision makers with the appropriate authority to make egress decisions based on that information. Performance-based approaches Prescriptive codes provide egress design guidance for a broad range of uses. Design flexibility is compromised in order to create such a comprehensive set of code provisions. In contrast, performance-based approaches combine first-principles fire engineering with evacuation estimates to assess whether occupants will be able to safely exit buildings for a range of fire conditions. Performance-based approaches require safety systems to be designed to meet specific fire safety goals for a range of fire events. This approach can result in design flexibility, as it affords the opportunity to align fire safety systems with overall building objectives. With this flexibility, however, comes an additional design burden, as analysis demonstrating that 26 Consulting-Specifying Engineer • SEPTEMBER 2008

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Consulting-Specifying Engineer - September 2008 Contents Viewpoint Letters News M/E�Roundtable Selecting Appropriate Egress Strategies Commissioning On-Site Electrical Systems Mentoring Control Engineers and Technicians Casting Call for Cx Case Study New Products Equipment Lifecycles Advertiser Index Green Space

Consulting-Specifying Engineer - September 2008

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