13 Annex D: Three-Route Verification Concept for Scotland
13.1 B.1 Introduction
13.1.1 The building regulatory system in Scotland is function-based. It is comprised in part of a set of functional Building Standards, which are supported by guidance provided in a set of the Technical Handbooks. The Technical Handbooks offer a range of prescriptive and performance-based approaches that, when followed in full, should be accepted by the verifier as indicating that the building regulations have been complied with. In addition, it is also acceptable to use alternative methods of compliance, provided they fully satisfy the regulations.
13.1.2 The responsibility for demonstrating that the regulations have been complied with – that the Building Standards have been met – rests with the Relevant Person, typically the building owner or developer. The owner may engage architects, engineers or others to develop compliant designs. For building structural design there is a Certification scheme, where a registry of Approved Certifiers is maintained, and certification is done by an Approved Certifier, without the need for regulatory review. This is in part supported by government recognition of qualifications for structural engineering. There is no similar system for fire engineering, as there is no qualification system and associated government recognition thereof. As such, designs are subject to verification by Local Authority Verifiers (LAVs), often with input from Scottish Fire and Rescue Services (SFRS) and sometimes from peer-reviews.
13.1.3 This approach sometimes creates challenges, in that there is not a clear way in which to identify ‘qualified’ fire engineers, some LAVs lack on-staff fire engineering expertise, there is a regulatory separation with respect to SFRS, and there is no particular system for peer-review. (See reports from Meacham (2016, 2017) for more discussion).
13.1.4 To help address the challenges and provide a system that is more robust, uniform in decision-making, and equitable, various suggestions have been tabled. These include: simplifying the Technical Handbook provisions to be simpler to use, especially for common buildings / building types, developing fire safety engineering verification methods for more complex building types and uses, and creating a centralized hub for review and verification of the most complex buildings, in particular those involving fire safety engineering approaches. It has been suggested that a system that employs all three of these approaches would be of value (e.g., see Meacham, 2016; 2017; Review Panel on Building Standards (Fire Safety) in Scotland - UK Review Panel Agreed Notes (January 2018 meeting) and International Sub-Panel Agreed Notes (February 2018 meeting)).
13.1.5 The following provides some preliminary concepts for how such a three-level verification approach might work, focusing on compliance with Standards 2.4 – 2.7 as a starting point. The approach largely follows the three-level approach outlined by Meacham (2017) as part of his report on competency criteria for verifiers of fire safety designs. For discussion purposes, the same basic levels are used, labelled here as: Level 1: Technical Handbook Compliance (Simple and Conservative), Level 2: Deviations or Alternatives (Verification Methods / Tests), and Level 3: Analyses (Fire Safety Engineering).
13.1.6 It should be noted that this type of three-level approach is already in place in other countries, notably Japan. In brief, the Japanese has three compliance routes: Route A, compliance with prescriptive deemed-to-comply provisions; Route B, simplified performance-based analysis, based on codified criteria and verification methods for egress, smoke filling, and structural fire performance; and Route C, full fire safety engineered designs, requiring approval by the Minister (approved expert panels). Additional discussion on the Japanese system is provided in Annex A.
13.2 Level 1 – Technical Handbook Compliance (Simple and Conservative)
13.2.1 In brief, the ‘simple and conservative’ approach is intended primarily for simple buildings with straightforward solutions, where no additional engineering analysis is needed. However, not every building is the same, and variability in design and solutions exist. Since life safety is a paramount concern, the simple approach should have some conservatism built in to account for variability in design and materials.
13.2.2 With respect to Standards 2.4 – 2.7, the primary focus is on inhibiting the development and spread of fire and smoke, and the building components of concern are cavities, internal linings, (fire) spread to neighbouring buildings, and (fire) spread on external walls.
13.2.3 A simple and conservative approach would be to require that all materials used as part of cavity enclosures, internal linings, and external walls, including fasteners, joint seals, and the like, must be non-combustible. This might also be extended to allowing limited use of combustible materials, if encased (enclosed) with non-combustible materials, and integrated into the building in such a way as to limit void spaces that could facilitate the spread of flame and smoke.
13.2.4 Such an approach would work well for many, but not all buildings. It may not be practicable or desirable for some, and/or it may be deemed excessively costly for others. In such cases, the other two verification routes are available.
13.3 Level 2: Deviations or Alternatives (Verification Methods / Tests)
13.3.1 For more complex buildings, or building uses in which the level of performance (safety) needs to be higher, due to increased life safety risk (e.g., due to occupant numbers, characteristics, vulnerabilities), increased hazards, firefighting challenges, or sustainability and resiliency objectives, there is often a need for some engineering analysis, or additional (and sometimes more comprehensive) testing to be conducted.
13.3.2 In many cases, the extent and/or complexity of engineering analysis and/or additional testing is not great, as there may only be a few deviations from the ‘simple and conservative’ solution. In a ‘traditional’ sense, these types of designs are often referred to as ‘variances’ or ‘deviations’. Deviations can often be addressed using ‘simplified engineering methods’, such as algebraic smoke filling equations, or hydraulic modelling of people movement, especially when conservative assumptions are included, appropriate safety margins are applied, and so forth. However, as the complexity and/or extent of deviation from the simple solution increases, the complexity of the engineering analysis and/or testing requirements increases. As complexity increases, cost and/or conservatism is likely to as well.
13.3.3 There are at least two distinct levels for this type of solution: single variable (or perhaps two at maximum), and multiple variable.
13.3.4 A single variable type of design problem, for example, might be a request for an extended travel distance, with all other fire safety requirements as per the ‘simple and conservative’ solutions, and ‘simple’ engineering analysis of people movement, with an appropriate margin of safety, is used in developing a solution.
13.3.5 From a material (component, system) perspective, a single variable type of problem might be consideration to use an ‘unapproved’ material (i.e., not subjected to the required standardised fire test method(s)) as an internal surface lining material. In such a case, an alternative fire test method may be proposed, and if deemed appropriate, used.
13.3.6 A multiple variable design problem might be a building in which there is a desire to reduce the total required number of exits (or width of required exit), based on installation of a smoke and heat venting system to maintain a smoke-free path of travel, and a more sophisticated fire (smoke) detection system and alarm system, to alert occupants sooner, activate the smoke venting, and/or other functions. This requires consideration of the scenarios, fire, design criteria, reliability of systems, and much more.
13.3.7 From a material (component, system) perspective, a multiple variable type of problem might be consideration to use an external insulated wall system, that includes unapproved’ material (in this case, perhaps combustible or limited combustible), as part of the wall system. In such a case, an alternative fire test method may be proposed, and if deemed appropriate, used (e.g., BS 8418, or ISO 13782 Part 2, or…).
13.3.8 One approach taken for a multiple variable type of ‘design’ problem in New Zealand was the development and implementation of a Compliance/Verification Method (C/VM2) for fire engineering analysis (MBIE, 2017). The NZ C/VM2 lays out specific fire scenarios, design fires, pre-movement assumptions, fire modelling assumptions, and more, and is intended to be applied for ‘typical’ performance-based design buildings; that is, buildings where several ‘variations’ from deemed-to-satisfy solutions (i.e., simple and conservative) are requested, and a uniform approach to fire engineering analysis is desired. There is some built in conservatism and limitations on applicability.
13.3.9 An approach for the multiple variable type of problem for a material (component, system), which is already cited in the Technical Handbook (non-domestic), Part 2: Fire for use in assessing fire performance of external walls is as in the example above – use of BR135 and BS 8414 as an ‘alternative’ approach to the guidance in 2.7.1.
13.3.10 “Alternative guidance - BR 135, ‘Fire Performance of external thermal insulation for walls of multi-storey buildings’ and BS 8414: Part 1: 2002 or BS 8414: Part 2: 2005 have been updated to include the most up-to-date research into fire spread on external wall cladding. The guidance provided in these publications may be used as an alternative to non-combustible or low risk classifications (as described in clauses 2.7.1 and 2.7.2) and for materials exposed in a cavity, as described in clause 2.4.6.
13.3.11 Clearly there is a wide range of potential ‘variances’ that fit this category: many that might have simple solutions and some that may have rather complex solutions. One way to manage this is to only permit designs, analyses, tests which are demonstrated to comply with broadly agreed methods which are appropriate to the regulatory purpose. Full implementation of such an approach would take time to carefully identify, vet and agree appropriate methods.
13.3.12 With respect to fire performance of external walls, however, it would seem appropriate that subjecting an external insulated wall system to one of the recognised standardised reaction-to-fire test methods for external insulated wall systems / external cladding systems would be appropriate, i.e., BR135 and BS 8414 or ISO 13782 Part 2 (and/or NFPA 285 and others, if deemed appropriate).
13.3.13 In the case of any verification approach associated with this level of verification, it is assumed that guidance would be developed as to what, when, where and how the analysis method, test method, or other verification method may be applied, including the documentation that is to be provided as part of demonstrating performance, and that guidance for verification and acceptance of any such designs, by Local authority Verifiers, is developed, implemented and available for use.
13.4 Level 3: Analyses (Fire Safety Engineering)
13.4.1 There will be times when ‘simplified’ verification approaches are not suitable, given the complexity of a building, complexity of a fire safety design, variability in materials used, cost of compliance with ‘simple’ verification methods, and more. In many of these cases, a full ‘first principles’ fire safety engineering analysis and design approach may be warranted, as described by guidance such as BS 7974, the IFEG, or similar.
13.4.2 While the details would need to be worked out, this level of verification would encompass any designs that substantially follow a ‘first principles’ fire safety engineering analysis and design approach, such as described by guidance in BS 7974 or the like. Such designs would be limited to those engineers with appropriate education, qualifications and credentials (to be determined and agreed), and would be subject to verification by those with appropriate education, qualifications and credentials (to be determined and agreed), or via a recognised central verification body, as has been tabled in previous discussions (e.g., see Meacham, 2016; 2017; Review Panel on Building Standards (Fire Safety) in Scotland - UK Review Panel Agreed Notes (January 2018 meeting) and International Sub-Panel Agreed Notes (February 2018 meeting)).
13.4.3 It would be anticipated that such analyses are applicable across a broad range of problems, including multiple variable design, material, component, system or assembly problems, which either fall outside of the scope of the ‘Verification Methods / Test’ level of verification, or which propose an alternative to such.
13.4.4 For example, considering again the fire performance of external insulated wall / cladding systems, and that the proposed verification scheme is adopted, the ‘simple and conservative’ approach would require that only non-combustible materials are used (with perhaps limited exceptions). The ‘verification methods / tests’ approach, however, would allow for those external insulated wall / cladding systems, that have successfully passed BR 135 and BS 8414 (or alternative, if permitted), to be accepted. Since such tests can be expensive, one might propose to take a ‘fire safety engineering’ approach. In such an approach, it might be deemed appropriate to test materials using small- or intermediate-scale apparatus and test methods, and combined with appropriate engineering analysis (e.g., flame spread modelling), present a credible design option.
13.4.5 Solutions using a fire safety engineering approach would be subject to a high level of adherence to guidance (e.g., BS 7974), including identification and treatment of uncertainty, clear definition of boundary conditions and limits of analysis and design, proper application of test results and computation models, and the like.