From the Technical Director The Practice of Performance-Based Design
By Morgan J. Hurley, P.E. | Fire Protection Engineering
Performance-based design is typically
implemented in one of two methods: (1) as a means to determine
equivalency to a prescriptive code or standard, or (2) as an approach to
achieve broadly defined fire safety goals and objectives. At present,
performance-based design is typically practiced in the former method.
However, for fire protection engineering to continue to rise in stature
as a mature engineering profession, the profession must strive for the
The present approach to performance based
design is necessitated by the prescriptive codes that are adopted in
almost every jurisdiction. A regulatory authority is required to enforce
the adopted code, and they generally can't choose to enforce a code
other than the adopted code.
Prescriptive codes typically contain an
"equivalency" or "alternate methods and materials" clause that permits
designers to use alternative approaches than those specifically
recognized by the code. These clauses require the designer to
demonstrate that the alternative approach results in a design that is at
least as safe as that achieved by following the prescriptive
Performance-based design has been practiced through the use of
equivalency clauses for decades, generally via an ad hoc manner that
varied from designer to designer and from jurisdiction to jurisdiction.
More recently, the development of performance-based design guidelines
has created a consistent framework that can be used to demonstrate
equivalency to prescriptive codes.
However, this approach does not allow fire
protection engineering to reach its full potential. First, even with a
consistent framework, the use of equivalency clauses is not perfect.
Determining whether a proposed design provides an equivalent level of
safety to prescriptive requirements frequently requires determining the
"intent" of the prescriptive requirement, which can be a subjective
task. Secondly, using a prescriptive code as the basis for performance
can hamper the maturing of the fire protection engineering profession.
A parallel that is frequently cited as a
possible course for fire protection engineering is structural
engineering.1 Structural engineering codes do not specify
member size and spacing as a function of building height and area.
Rather, structural codes specify the loads that a building must
withstand as a function of the building type and reference design
methods that can be used to ensure that a structure can support the
specified loads. Engineers have wide latitude in designing a building
structure to meet the requirements of the code.
The structural engineering parallel for
fire protection engineering is desirable for a number of reasons. First,
engineers would have far greater latitude in developing fire protection
strategies for buildings. This would foster innovation while ensuring
that fire protection is tailored to the needs of the building and the
community. Second, greater engineering rigor is brought to bear in
solving fire protection problems.
The fire protection engineering profession
has made significant strides in the last decade towards developing the
infrastructure necessary to support performance based codes.
Performance-based codes have been published in several countries, and
numerous design guides have been published that provide accepted methods
for designing to meet the requirements of the performance codes.
However, in many cases when performance codes are used today, designers
typically refer to prescriptive or deemed-to-satisfy requirements for
large portions of a project.
It will be a while before the fire protection
engineering profession is ready for performance-based design on all
projects, without reference to prescriptive codes. However, it serves as
a good goal to which the profession should strive.
Lucht, D., "Public Policy and
Performance-Based Engineering," Proceedings of the 1996 International
Conference on Performance-Based Codes and Fire Safety Design Methods,
Society of Fire Protection Engineers, Bethesda, MD, 1996.