CROSS Safety Report
Fire protection of stair structure
A reporter is concerned about the lack of structural fire protection in a fire escape stair, which is assumedly attributed to a lack of coordination between the architect and the structural engineer.
Key Learning Outcomes
For the design team:
- Establish a matrix of design responsibilities to avoid confusion
- Ensure communication between the teams so that all aspects of the design are fully addressed
- Building control approval does not absolve designers from their responsibilities
For potential buyers:
- Consider introducing an independent third-party review to check the suitability of the chosen solutions
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The reporter was employed by a potential buyer to review and report on a hotel building which was being modernised. This process led to a new fire escape stair being constructed in the original central courtyard, as part of the building’s new fire strategy.
This fire escape was forming a separate compartment through fire-rated walls. However, the reporter recognised a potential issue of structural performance in case of fire when they realised that the supporting steel structure of the stair was going through a plant room – which is considered an area of elevated risk – without any structural fire protection being present in this location. This raised the concern that a fire in the plant room could affect the loadbearing capacity of the escape stair and subsequently undermine the compartmentation achieved through any separating element that is being supported by this steel structure. As a worst-case scenario, the structural collapse of the stair was also considered a possibility.
a worst-case scenario, the structural collapse of the stair was also considered a possibility
The reporter’s worries were further exacerbated by the fact that the structural drawings “were silent on fire protection”, and even though the architectural drawings covered issues of fire compartmentation they did not present any elements’ fire rating. This led the reporter to include the concern in their review in order for the issue to be actioned by any future buyers.
Holistic approach in design process
The reporter is of the mind that there was a lack of coordination between the architect and the structural engineer, which caused both of them to not review this design aspect accordingly. This goes against the need for a holistic approach in the design process, which is essential in addressing design issues for the building as a whole and not as separate functional entities.
Expert Panel Comments
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Commonly, a stair structure does not need to have applied fire resistance where it is within a low-risk enclosure. In this case, it is not clear why the structural steel in the plant room doesn't have any fire protection given how that would normally be required, as the reporter suggests. If there is no fire protection to that structure, then that might be a breach of normal standards, unless there are other mitigating factors that are not mentioned in the report.
It can also be very common for drawings to omit structural fire resistance ratings, and to rely on a note. Of essence in this case is not only that there was a lack of overall thought and control, but also that when the issue was raised there was a lack of professional care on the part of the designers. They should have realised and acted accordingly.
In general, there is an excessive reliance on the existence of building control approval which is no guarantee that a building is safe. Building control approval does not absolve designers from their responsibilities.
lack of professional care on the part of the designers who should have realised the significance of the issue
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