Performance-based design achieves fire, life safety

Specifying a single product or system within a facility using a performance-based specification, when the design is subject to performance-based design (PBD), can fundamentally reduce the level of safety achieved.

05/23/2018


This article has been peer-reviewed.Learning objectives:

  • Understand the factors that can play a part in performance-based design (PBD).

  • Explore where critical changes to specifications can result in unintended changes to levels of safety.

  • Know the impact early design decisions can have on achieving safety standards and minimizing waste.

  • Learn from case studies where poor design approaches resulted in waste.


Figure 1: This atrium requires a specific type of sprinkler on one hazardous side that was different from the lower hazard side, resulting in larger pressure losses and larger pipe-size requirements. All graphics courtesy: Simon GoodheadWhen creating fire specifications for a building project that includes performance-based design (PBD), an uninformed engineer of record can fundamentally change the level of safety achieved. While the engineer for the PBD will attempt to include all stakeholders, it is the responsibility of all parties to communicate the design requirements of the PBD, and the specification language associated with the design requirements to ensure safety is maintained.

The process of PBD is a lesser-known path for building design; the following discusses the concepts of PBD, the parties involved, implications of decisions, and the importance and implications of specification development and changes.

If the engineer of record for the PBD follows industry-acknowledged processes, such as the Society of Fire Protection Engineer’s (SFPE) Engineering Guide to Performance-Based Fire Protection, then all stakeholders (including the engineer of record for specification development) will come to the project informed about the various aspects of the PBD. It is therefore the engineer of record’s responsibility to make all parties aware of product changes or updates to performance-based specifications that are broad in nature.

With a holistic approach to PBD, all members of the design team need to be aware of how PBD can impact their approach to design and specifications. It is more likely that the engineers who are not aware of PBD may “over specify.” Over specifying may result in both wasted cost and materials, and also may in some instances actively work against the PBD, thereby reducing levels of safety.

Figure 2: Georgia Tech’s Clough Undergraduate Learning Commons atrium relied on fire modeling to demonstrate the tenability of the space for occupants egressing.Performance-based design

PBD in the context of fire safety is absent from many codes including the International Building Code (IBC), International Fire Code (IFC), and International Mechanical Code (IMC). NFPA 101: Life Safety Code, however, introduces the “performance-based option,” referring to the consideration of fire safety performance as a method of generating design/egress parameters for a building. That stated, PBD also is a term used in many disciplines related to using a performance target as the basis for the design (structural, mechanical, etc.), and so the fundamental approach on a macro level can be viewed as universally similar.

Most definitions would speak to using science and engineering techniques applied to a problem with the goal of achieving a performance that is agreed to by the stakeholders involved. When looking at how alternative means and methods are applied, that performance may be benchmarked to a predetermined level of safety/standard with the intent for the design solution to be commensurate or superior to that benchmark.

So, where is that performance metric derived? For fire safety following the performance-based option in NFPA 101, as an example, the performance required is to provide an “environment that is reasonably safe from fire.” When using true PBD, the goals and objectives must be defined by the group of stakeholders as one of the first steps. The stakeholders should include not just owners, designers, and approving authorities, but also users, insurers, and property management, to name a few.

Figure 3: Georgia Tech’s Clough Undergraduate Learning Commons design allowed complete openness of three atriums and corridors resulting in half the exhaust rates compared to calculated approaches, and reduced inlet air path area requirements.Through the stakeholder communication process, the design parameters can be aligned to meet many needs, rather than purely meeting what is intended to be achieved by the prescribed method in the applicable code.

The IBC, IMC, and IFC introduce the alternative means and methods section in Chapter 1. Depending on the applicable edition in the jurisdiction of the engineer, the specific subsection of the code will vary. In each instance, Section 104.11 of the code states that the level of performance or standard of safety should not be reduced:

“ … the proposed design is satisfactory and complies with the intent of the provisions of this code, and that the material, method, or work offered is, for the purpose intended, not less than the equivalent of that prescribed in this code in quality, strength, effectiveness, fire resistance, durability, and safety … ”

PBD approaches, when including the stakeholders in determining the performance requirements, may result in owners and developers citing construction cost and time as a factor. Insurers may cite property loss. Users may cite aesthetics. The approving authorities may end up citing the above statement as their goal from a safety perspective. So PBD in the United States may result in the following question: When applying alternative means and methods as the standard to achieve, what is the safety performance of the code?

To answer the question of “what is the safety performance of the code?”, a preliminary question may be: What information is needed to achieve the PBD solution? Some of the key factors and questions we must consider to achieve a PBD solution include:

  • Establishing stakeholder buy-in. Is everyone able to agree to the approach proposed? The last thing a designer should want is to complete a design only for it to be rejected by the lead designer, owner, or authority having jurisdiction (AHJ).

  • Determining the performance of the prescribed method. Use quantified methods to establish the performance of the prescribed method. This allows the designer to establish the level of safety that can be achieved by the prescribed method.

  • Specifically outlining for the AHJ and lead designer what the PBD may include and identifying the goals of the exercise. This is important as it is the second point at which major issues can be ironed out ahead of extensive effort. This phase may include a design brief or statement of work.

  • Reviewing the system or process. Are the systems or processes connected to surrounding systems or adjacent processes? Understanding this consideration starts to define the scope of the proposed alternative method. For example, smoke damper operation (opening or closing) may impact a smoke control system performance.

  • Completing the analysis and quantifying the performance of the proposed design. In almost every instance of a PBD, this should be an iterative process. Even if the first analysis passes, consideration of variables should reveal at what point the analysis may fail.


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