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CROSS Safety Report

Ineffective fire socks

Report ID: 1115 Published: 10 March 2022 Region: CROSS-UK

This report is over 2 years old

Please be aware that it might contain information that is no longer up to date. We keep all reports available for historic reference and as learning aids.


A reporter shares their concern about how the quality of fire stopping in a residential project was found to be  substandard and the potential reasons that led to this happening.

Key Learning Outcomes

For project managers:

  • The Regulatory Reform (Fire Safety) Order 2005 defines the Responsible Person who has to ensure that they use a competent professional to do the work

For the construction team:

  • Be aware that passive fire protection components should be installed in accordance with the manufacturer’s specifications
  • Consider introducing a quality assurance process that covers the correct use and installation of fire protection products and components

Architects and lead designers on projects:

  • Establish a matrix of design responsibilities to avoid confusion

Site Engineers:

  • Ensure communication between the teams so that all aspects of the design are fully addressed

Fire Engineers:

  • When contracted to do so, attend site at key stages to inspect the works to ensure they are being built in accordance with the design

Full Report

Find out more about the Full Report

The Full Report below has been submitted to CROSS and describes the reporter’s experience. The text has been edited for clarity and to ensure anonymity and confidentiality by removing any identifiable details. If you would like to know more about our secure reporting process or submit a report yourself, please visit the reporting to CROSS-UK page.


During the construction of a ‘general needs’ block of flats, some quality issues were identified – subsequently, concerns were raised. To address these a professional was hired to investigate and review the standards of fire stopping in the project. The works included the construction of cavity walls with a masonry leaf. The concerns were principally related to wall cavity socks, which at this stage of construction were partially enclosed.

Potential breach of compartmentation

The review concluded that the standard of installation was poor in a high percentage of the locations surveyed. This further enhanced the concern that most of the cavity barriers already fitted were not appropriate to the limitations and standards required by the manufacturer's technical specifications. It follows that the potential impact of this is the propagation of fire through the cavity, which can lead to a breach of compartmentation. This raised some serious concerns because the intention was to implement a 'stay put' evacuation strategy, whose utility and intended function would be obviously precluded if there is any potential for the structure to inadequately inhibit the spread of fire beyond the flat of origin.

Checking the installation of fire socks

The reporter attributes this to the principal contractors completely relying on the masonry sub-contractors to install the fire socks competently in an appropriate manner, without anyone overseeing the quality of installation or engaging with an appropriate third party to certify the works. The available experience suggests that this is an all too often approach to the installation of fire socks during the construction of cavity walls with a masonry leaf.

To uncover the motivation behind this practice, says the reporter, the issue was discussed with site and project managers that work on similar scale projects. From these conversations it was indicated that synchronising the cavity wall construction with third-party fire stopping inspection would introduce delays into the critical path, which is the sequence of dependent tasks that form the longest duration for project completion; any delay can incur additional costs, which is to be avoided.

The findings of this review forced the principal contractors to make good all deficient construction by hiring the services of a third-party fire stopping sub-contractor, which will of course be reviewed again to ensure its quality. This led to a considerable overspend in the overall project, likely to result in significant financial losses to the principal contractors.

The findings...led to a considerable overspend...likely to result in significant financial losses to the principal contractors

Expert Panel Comments

Find out more about the Expert Panels

Expert Panels comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-UK Expert Panels page.

This is another useful report about the incorrect installation of passive fire protection components, as it adds to the weight of the existing reports around this issue and supports any previous CROSS response. Once again, the need to employ competent people to carry out the work, along with thorough inspections during construction and extensive record-keeping in all phases cannot be overstated.

The Principal Designer, under the Construction Design and Management Regulations 2015, is required to recognise the significance of these fire stops, and accordingly emphasise the importance of correct installation, ensuring the appropriate quality of the work through any means available. It is the panel’s general impression that Principal Designers do not carry out site inspections to a degree that would ensure the elimination of issues such as the one raised in this report.

Finally, experience has shown repeatedly that spending the money to do it right the first time is always cheaper than spending the money to fix it. 

experience has shown repeatedly that spending the money to do it right the first time is always cheaper than spending the money to fix it

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