Quantitative performance requirements contain quantified criteria that are used as a ready means of assessing compliance of the alternative solutions with the relevant performance requirements. The benefit of writing performance requirements in quantified terms is that direct comparisons can be made to the expressed numeric or measurable values within the requirement.
While this form of regulation is more readily assessed, is does not allow total flexibility and practitioners are often unduly constrained by having to work to the expressed quantified criteria. For example, in certain instances compliance with a performance requirement that states that ‘all occupants within a fire compartment must be able to be evacuated to a place of safety within three minutes’ may be inappropriate; while compliance may be readily assessed, the time period stated in the performance requirement may be unsuitable in particular circumstances, such as where it can be demonstrated that untenable conditions resulting from a fire may not be present in a fire compartment for five minutes from fire initiation.
In this case it may be more appropriate to express the requirement in a qualitative manner, e.g., ‘tenable conditions must be maintained within a fire compartment for sufficient time to enable all occupants to evacuate to a place of safety’. Assessment of proposed designs would require more supporting evidence, however, practitioners would have the flexibility to design appropriate systems specific to the circumstances applicable to the individual design.
In some instances the use of qualitative performance requirements in building regulations may arise from an absence of consensus among the technical experts developing the performance requirements with respect to measurable criteria that are to be included in the provisions. While this outcome is understandable the ability of some industry practitioners to agree on the propriety of proposed designs can be tested when complex designs are offered for consideration.
While performance-based building codes offer flexibility and support innovation, there are many designers who simply wish to use traditional recipes for design and construction.
To accommodate these designers, performance-based building codes should incorporate a suite of recipes that have been given the approval of the regulatory authorities and are acceptable without further validation or proof of suitability. These recipes are contained within the third tier of the performance-based structure.
Objectives
Performance requirements
Building solutions
Deemed-to-satisfy provisions
Alternative solutions
9.7.3 Tier 3 – building solutions
The third tier of the structure contains the optimal means that can be used to satisfy the performance requirements. Designers may formulate their own recipes to comply with the performance requirements, or they may use traditional pre-ordained recipes.
The self-formulated recipes are often referred to as alternative solutions. The onus for validating an alternative solution and demonstrating compliance with the performance requirement is placed on the person seeking approval of the design.
The traditional pre-ordained recipes are often referred to as deemed-to-satisfy provisions and these need no further validation or substantiation. In many instances a deemed-to-satisfy provision may refer to a referenced standard (i.e., a standard named in the relevant code), or other external document, that contains an acceptable means of complying with the mandatory performance requirements. For instance, structural design performance requirements can be met by the use of appropriate standards, such as ISO standards, that are simply adopted by reference within deemed-to-satisfy provisions.
Designers should be able to use any combination of alternative solutions and deemed-to-satisfy provisions in order to comply with all relevant performance requirements so a performance-based regulatory regime should contain at least three tiers of provisions. The top tier provides information on what the regulatory provisions are endeavouring to achieve, the second tier specifies what is required to be achieved, and the lower tier provides ways in which those requirements may be achieved. Figure 9.1 shows a basic three tier structure.
9.8 Fire-engineered building designs
The development of complying alternative solutions may be undertaken in any manner that is satisfactory to the approval authority. The methodology utilized by the designer will Figure 9.1 A three-tiered regulatory structure.
generally need to involve an acceptable process which can be supported by appropriate documentation and which ultimately leaves the approval authority with no doubt as to the suitability of the alternative solution. The following discussion of fire-engineered design provides an example of a process by which certain alternative solutions can be generated and assessed.
The application of fire engineering technology is recognized throughout the world as an acceptable method of developing alternative solutions to meet relevant performance requirements for fire safety in building design. In this context, fire engineering can be described as a design methodology by which engineering principles are applied to the evaluation of hazards identified within a building and then to the design of appropriate methods of protection to deal with those hazards.
This design concept is the same as that inherent within the content of most building codes, however, traditional building codes have, through necessity, adopted a conservative approach in order to be generically appropriate across a particular class of building, whereas fire engineering allows a similar process to be applied to individual buildings within a particular class.
While appropriate fire engineering technology has been available for some time, its use in developing alternative solutions has generally been limited to applications involving objections, dispensations or appeals against the content of prescriptive provisions, largely because of the prescriptive format of most traditional building codes.
Following the introduction of performance-based building regulations in various countries throughout the world, the use of fire engineering technology as a tool for the development of alternative solutions has flourished. This increased use is due, at least in part, to the change in the content of the building regulations, as a major portion of the content of building codes address requirements for adequate standards of fire safety in the design and construction of buildings. Many major building projects throughout the world have been the subject of fire-engineered designs, including many of the buildings constructed for the Sydney Olympic Games.
Fire engineering technology facilitates the development of alternative solutions that meet the same objectives as those inherent within regulations and designers continue to explore opportunities to introduce options that accommodate their needs better than traditional deemed-to-satisfy provisions.
Another contributing factor to the recent surge in fire-engineered designs is the ongoing refinement of the technology which supports fire engineering, particularly computer technology. Advances in technology have allowed the continuing development of mathematical modelling programs that are more user friendly and more accurate than their predecessors.
Significant developments in fire engineering in Australia have been implemented through the Fire Code Reform Centre Limited (FCRCL), an independent company established to administer and direct a defined, fire engineering-related, research program.
One of the significant initial outcomes of the FCRC was the publication of Fire Engineering Guidelines (FEG) (FCRCL, 1996). This document can be described as a process document in that it outlines procedures and methodologies for use by suitably qualified and competent practitioners undertaking fire-engineered designs. It is important to note that use of the FEG requires professional knowledge and engineering judgement and therefore it is not a document that should be used by practitioners without appropriate expertise. The document is, however, recommended reading for all practitioners as it
provides a substantial base for gaining an understanding of the concepts and considerations involved in the development of an appropriate fire-engineered design.
Basically, the FEG is intended for use during the conceptual stage of a project and is suitable for application to both existing and new buildings. The conceptual stage can be divided into a number of steps commencing with the preparation a fire engineering design brief (FEDB) and finishing with the production of a fire safety systems report. It is during the preparation of the FEDB that relevant parties to the design and approval of the project confer and reach agreement on matters such as design objectives, acceptance criteria, hazard identification, fire scenarios to be analysed, trial concept designs and the method by which designs will be evaluated.
Following the FEDB process trial designs can be analysed and evaluated through comparison with the previously agreed acceptance criteria. In the event that the design is not appropriate, the later components of the process can be repeated with a new trial design. When a design is developed that meets the acceptance criteria, the approval process should be faster as the approval authority has been a party to the preparation of the FEDB in which the acceptance criteria were mutually agreed.
During the application of the FEDB process to more complex projects there may be instances when some of the relevant parties consider they do not have sufficient expertise to actively participate in the preparation of the brief, or there may be instances when a fire-engineered design is developed without the application of the FEDB process and the approval authority considers it has insufficient expertise to adequately assess the design.
In either instance it is essential that the relevant parties are represented by an appropriately qualified person to either participate in the FEDB process, or to assess the propriety of a fire-engineered design.
Other issues that must be addressed include:
9.8.1 Selection of appropriate computer software
Approval authorities need to be satisfied that a proposed design has been developed using appropriate software and that the fire engineer is suitably experienced in the use of the software.
9.8.2 Selection of appropriate input data
If the FEBD process is not followed then both the designer and the authority must assess the validity of the input data, such as the characteristics of the ‘design fire’, used in producing the design.
9.8.3 Expectations of computer software
While mathematical models can provide reasonable predictions or approximations of likely outcomes, the process requires the expertise of experienced practitioners to ensure that there are adequate safety factors in the design outcomes which can accommodate the limitations of the design tools.
9.8.4 Preparation of submissions for approval of alternative solutions
Some of the most difficult assessments to be made are those regarding both the extent and content of submissions made by designers to approval authorities in support of alternative design proposals. This applies equally to documentation provided volun-tarily by applicants as well as that required by the authority.
It is desirable for all relevant parties to participate in discussions at a preliminary design stage in order to prepare an agreed platform for the development and approval of design proposals. This is called pre-lodgement consultation. Generally, when developing building designs using prescriptive regulations, pre-lodgement consultation can be kept to a minimum as quantified design criteria are clearly set out and compliance is easily assessed. This is not the case when using performance require-ments in which there may be no quantified criteria and the interpretation of the approval authority as to what is necessary to meet those requirements may vary significantly to that of the designer.