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CROSS Safety Report

The potential for expertise asymmetry in aspects of the design of tall buildings in the UK

Report ID: 1143 Published: 20 February 2023 Region: CROSS-UK


A reporter is concerned about the potential for 'expertise asymmetry' in the fire safety domain, with a focus on smoke control systems.

Key Learning Outcomes

For building safety approval bodies, regulators, enforcing authorities:

  • Organisations with a duty to oversee building safety should have suitably competent persons to check and analyse proposals and/or building work
  • This is particularly pertinent when the proposal/work is not for a common building situation 

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A reporter is concerned about the potential for 'expertise asymmetry' in the fire safety domain, with a focus on smoke control systems.

The phenomenon of 'expertise asymmetry' has been observed as a key challenge in the regulation of complex technologies. It stems from the fact that there may be differing levels of knowledge and skills between the regulators and those who are regulated. If conditions exist (such as the lack of resources) so that the regulators cannot maintain high levels of technical competence/expertise/skills, then they must rely on data and analyses provided by the people they are regulating. This concept has been explored and discussed in the fire safety engineering profession by Spinardi.

In England, this could be observed in the established approval authorities on this topic, and the Health and Safety Executive (HSE) who have an emerging role as the Building Safety Regulator conducting reviews of designs at Gateway 1 (RIBA Stage 2 / planning).

It is acknowledged that approval authorities are requested to review and comment upon a vast variety of the technical issues covered in the suite of Approved Documents and other technical standards, not just fire safety, so there is a limit to the depth of detail their review can go. It is the role of the designers to ensure their solutions comply with the Building Regulations and it is the role of the approval authorities to ensure all processes are followed, while asking key questions on the design philosophy and interrogating the fundamental assumptions that each solution is based upon.

The reporter’s motivation is to raise awareness about the potential for this phenomenon to occur even between designers who are conducting peer reviews. Given the significant changes that are happening in the regulatory domain following the implementation of the Building Safety Act 2022, it is considered vital to ensure that designers who may be conducting peer-reviews are aware of these issues and fully interrogate the technicalities and details of such proposals when called upon by clients or approval authorities.

Failure by designers

The reporter is concerned, because they have experienced cases where designers for tall residential buildings have proposed pressurisation systems at an early stage, without consideration of any potential project-specific complexity and whether the technical solution can and will be achievable in the final design. The designers are of the mind that citing and presuming compliance with the relevant guidance documents and technical standards is an adequate approach. The reporter's opinion is that this might not always be the case. It is based on an argument revolving around the topic of what is a 'common building situation', and the relevant application of technical guidance. If a project is not considered a 'common building situation', then a more sophisticated approach is warranted.

In general, the reporter thinks that there is a failure by some designers to recognise that tall residential buildings are likely to be complex and that guidance intended for common building situations should not be assumed to automatically deliver safe solutions. Instead, they support the opinion that safety needs to be demonstrated for such buildings through a proper hazard assessment protocol, such as by adopting the process set out in BS 7974. According to the reporter, this is a more appropriate way to demonstrate robustness in the provisions for smoke control in tall residential buildings.

Technical basis for concern

In the reporter’s experience, no modelling of pressurisation systems is typically proposed by designers, due to the presumption that by designing to 'code' is adequate. Additionally, it remains unclear how this modelling would be carried out reliably and objectively using the current tools deployed in the market. For example, the Fire Dynamics Simulator (FDS), by far the most commonly used Computational Fluid Dynamics (CFD) modelling tool, does not have validation cases for pressurisation systems. In addition recent releases (not the current, but some previous releases) had noted issues with the resolution of pressures within the model. This same problem extends to other more general CFD codes. Therefore, any approval or design relying upon demonstration by CFD modelling may not have a valid basis of compliance, unless all the limitations are explicitly recognised and addressed accordingly within the scope of each tool.

Furthermore, it is expected that designers should be confident that all leakage paths have been considered in their analyses, such as the existence of smoke seals on doors. However, any future change to the building could have an impact on leakage paths or other factors that the smoke control system is dependent upon, and that would require a reappraisal of the system. This would make it extremely hard to demonstrate during the early design stages (when such a solution is chosen and relied upon) that a coherent and reliable system is in place.

There are other considerations that can impact the specifications and appropriateness of the chosen smoke control system. One is the provision of a defined level of protection that provides an adequate refuge to persons who cannot use the stair (by reference to the evacuation timeline). Another is the consideration of a scenario where the sprinklers have not activated successfully, or are overwhelmed, and how subsequent firefighting actions can impact the operation of a smoke control system. Finally, the potential impact of the failure of key components, such as dampers and fans, on the system’s performance during means of escape and firefighting periods is another case for consideration mentioned by the reporter. These examples follow the thinking process of recognising common modes of failure in mutually dependent systems and taking measures to ensure their sufficiently robust and automatic operation.

The reporter is of the mind that designers should be made aware of these and similar challenges (through CROSS or other conduits), in order to constantly be in a position to thoroughly interrogate any solution that their peers propose at any stage. This would minimise the phenomenon of 'expertise asymmetry' by assisting, through their specialist knowledge and expertise, approval authorities in their role of ensuring a robust process is in place.


The reporter’s motivation for submitting this CROSS report is to place in the public domain, in a manner that relevant stakeholders should be aware of and can access, concerns and potential solutions regarding smoke control in tall residential buildings. By doing so those designing, building, and approving such structures can meet the fire safety needs of future residents. The reporter thinks that this can be done through the allocation of adequate resources to the approving authorities, the production of guidance notes on this topic and others of similar criticality, and assigning importance to fire safety in the early design stages of such schemes.

Expert Panel Comments

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The panel agrees that there needs to be a clarification in the perceptions around the roles of each stakeholder in the design process. Approval authorities are expected to have an expertise in the building control process, rather than a knowledge of every technical detail that the vast variety of design solutions can entail.

Building control should not be perceived, especially by designers, as a checking process that replaces in-house or independent checks

Building control should not be perceived, especially by designers, as a checking process that replaces in-house or independent checks which are meant to pick up errors in the detailed calculations; the truthfulness and accuracy of these is the responsibility of the designers. The building control role is perceived by the panel to involve the probing of the approach followed and assessing the big picture of the design solution – it is unrealistic to expect or demand that building control have the skills that are found in specialist and expert peer review, which is why each step has its role in the approval process.

The same argument could be made for the Fire and Rescue Services as statutory consultees under Part B, where one consultee cannot be specialist in every area of design and fire engineering; it is, again, about asking the right questions.

The ultimate responsibility lies with those designing and constructing premises, and where systems that involve complexity and interactions, or other alternative approaches, are proposed there should be an informed independent third party peer review.

The panel agrees that caution is needed when active systems are being used that rely on good management from a testing and maintenance perspective to operate as required. In addition, such systems to require regular checking to ensure they are still fit for purpose. The Building Regulations do not impose management requirements and assume proper management, as it is clearly stated in ADB, with the caveat that unrealistic and/or unsustainable management regimes cannot be considered to have met the requirements of the regulations.

CROSS has published reports on cases that emerged where premises and fire safety systems are being designed, installed, managed and maintained poorly. The Regulatory Reform (Fire Safety) Order 2005 can also have limitations when addressing issues under Building Regulations. It is up to the designers to consider the maintenance needs and the reliability of their proposed solutions so that additional measures can be incorporated to compensate for all cases, on a case-by-case basis.

This report is also of relevance regarding the new regime under the Building Safety Act 2022 as overseen by the Building Safety Regulator, specifically the Safety Case scenarios. With the limited information available so far, it could be expected that support for a Safety Case will need to explicitly demonstrate safety with appropriate evidence, similar to the suggestions the reporter made on the limitations of modelling and recognition of common modes of failure in mutually dependent systems.

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