CROSS Safety Report
Supporting constructions under fire doors and screens
A reporter raised the issue of interpreting test results for understanding the performance of system glazing fire doors and screens in raised access floors or lightweight construction methods.
Key Learning Outcomes
- When designing compartment walls using lightweight means of construction, close attention must be paid to the structure supporting fire doors or glazed panels
- Designers may be responsible for the performance of these junctions in a fire
- Desktop assessments of systems against one or more standards, when the materials used may not have been considered in the original test, may result in safety being compromised
- Adhering to design details for supporting structures beneath fire doors and other compartment wall elements is critical
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The reporter is concerned that an outdated understanding of appropriate supporting constructions for glazed fire doors and screens, based on steel-framed systems, are still in play in the fit-out industry in the UK.
System glazing is fire tested according to European standards with clearly defined supporting constructions. In these cases, the threshold is typically a concrete block and may be lined with calcium silicate. None of the door systems will have been fire tested on anything other than this firm form of the threshold.
The fit-out industry often installs raised access floor systems without breaking them at the threshold of a fire door
The fit-out industry often installs raised access floor systems without breaking them at the threshold of a fire door. The compartmentation is maintained with a fire-rated batt-type barrier in the floor void, directly below the fire door. The reporter considers this form of construction for a fire door threshold to be of unproven performance because it extrapolates significantly from two other tests.
While a raised access floor may have been the subject of a fire test, it will have been according to the test standard for raised access floors, where the fire is below the floor and may only have been limited to the reduced time temperature curve at 500 ºC. This is out of context with a vertical fire test of a door or screen where the temperature at full term will exceed 850 ºC. The raised access floor fire test may have included a load on the top surface but, again, this is intended to simulate the effects of a normally loaded floor, not the behaviour of a steel-framed door under the effects of extreme heat.
The reporter believes the expected performance of that system cannot be properly assessed through the two independent system tests (raised access floor test and fire door test) due to their perceived lack of representativeness of the final application. It should be considered by designers that this form of construction may not have been available, or considered, when the tests were conceptualised. The reporter thinks that without any representative fire testing, there is no way to predict the behaviour of the floor system or its interface with the door, and integrity failure cannot be confidently ruled out.
The reporter assumes there may be a number of causes for this issue:
- Ignorance of the testing standards and the test evidence behind the door systems
- Programme constraints requiring the raised access floor system to be installed as a blanket without planning the fire door breaks
- Main contractor budget constraints meaning they are unwilling to consider replicating the test threshold configuration while they are using lightweight constructions on the project
The reporter would like to have the assurance that their interpretation of the correct practice is accurate. They have never seen any directive or authoritative narrative that confirms that a raised access floor should not be broken on either side of a suitable threshold construction beneath a fire door, as illustrated in Figure 1. They would also welcome any comments or suggestions about systems that ensure adequate performance without a threshold break. In any case, it is useful to bring the issue forward for the education of the wider community on this, and potentially similar, issues.
Expert Panel Comments
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Testing and standards
This is a serious issue with widespread ignorance of the problem.
Raised floor systems are generally metal-wrapped chipboard, or calcium silicate boards, with pedestals to raise them up and create a void. The Panel are not aware of any tests being carried out on these in conjunction with fire doors. It is critical that the performance of the pedestals is considered part of the system.
This is a relatively new approach, previously contractors would have screeded stair lobbies or installed the doors within blockwork walls, with the raised access floor abutting the solid construction at the threshold. It is understood that contractors wish to remove wet trades from the site and so everything is lightweight plasterboard and raised floor carrying through. People have tried lots of details, and it is challenging to try and take the tested plasterboard wall detail under the door because it is not robust enough for foot traffic.
test reports should be carefully reviewed to ensure that the fire tests are actually applicable for the end use
Compartmentation should not be compromised in such a scenario and the test reports should be carefully reviewed to ensure the fire tests are actually applicable for the end use. One robust solution could be to use masonry or a concrete upstand at the line of the threshold, but whatever solution is proposed, those designing these systems must be aware they are responsible/liable for their performance in the event of a fire.
This may be a case of unthinking extended application of a fire testing standard. It is also potentially a case of a fire testing standard being applied in situations that were never intended - or even envisaged - when the test standard was developed.
Identifying wall makeup
An associated matter is the identification of the makeup of walls. The Panel suggests that there should be labels on all fire compartment walls. This should help prevent future breaches and might ensure holes drilled for cables or other services are suitably fire-stopped afterwards. It could be linked to an asset management system, via bar or QR codes, and added to the building information model (BIM) for the building.
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