Fire Safety Considerations for Modular Timber Construction 

 

The University of Edinburgh undertook a series of five medium-scale fire experiments performed on 1m3 mass timber boxes. These experiments were performed to develop an understanding of the response of mass timber-lined compartments in the event of a fire, to quantify the differences in fire dynamics and potential for ongoing burning after consumption of the movable fuel load within the compartments, and to inform the experimental configurations to be used – and experimental parameters to be varied – in the full-scale fire experiments performed in February 2022.

The combination of experiments undertaken enables investigation of the effects of exposed timber area and configuration on fire dynamics in such compartments. The additional experiments explore the performance of the three different engineered timber products supplied for this project.

The three different engineered timber products include Cross-Laminated Timber (CLT), Glue-Laminated Timber (Glulam), and Nail-Laminated Timber (NLT) panels. All of the panels used in this study were 1 m by 1 m in size, however the thickness of each product varied. The CLT panels have a total thickness of 99 mm (3 layers of 33 mm each), the NLT has a “corduroy” visual effect with alternating thickness of 85 mm and 115 mm, while the glulam has a thickness of 125 mm.


Principle Outputs

  • In the majority of cases global combustion ceased shortly after the consumption of the movable fuel load in the post-flashover period

  • In one case (CLT side walls and ceiling) a secondary flashover was observed

  • Observations have influenced the compartment configuration for the large-scale testing

  • These larger compartments will involve two exposed timber surfaces (back wall and ceiling)

  • The back wall will always be formed by a CLT panel however all three mass timber products (CLT, Glulam and NLT) will be used in the ceiling

Conclusion

Variations in the total energy release and post-flashover combustion behaviour were observed as the exposed Cross Laminated Timber (CLT) area and configuration were varied. The peak total heat release rate varied linearly with the total area of exposed CLT surfaces with a secondary flashover observed in the compartment with the greatest exposed CLT area (both side walls and ceiling).

Differences in the fire dynamics were also observed where a Glued Laminated Timber (GLT) ceiling panel was used in place of a CLT panel, with a reduction of the peak total Heat Release Rate occurring. The performance of the different mass timber products will be explored further in the upcoming large-scale fire experiments.


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