On 17^th September, Dr Andrea Lucherini joined the Fire Science Show podcast hosted by Wojciech Węgrzyński to discuss an aspect of fire development that is often ignored: fire decay and cooling. While most structural fire safety engineering focuses on the fully developed phase of post-flashover fires, Andrea explained that structural failures can occur after the flames appear to be under control. He highlighted a case where seven firefighters died when an underground reinforced concrete structure collapsed during the cooling stage, not at the fire’s peak.

Andrea described how different materials can respond during these phases:

• Reinforced concrete structures may reach the highest temperatures in the steel reinforcement during cooling.
• Steel structures can suffer severe tensile forces as they contract, especially at connections.
• Mass timber suffers the reduction of mechanical properties at relatively-low temperatures and may never fully enter a cooling phase without careful design.

He also noted that as smoke clears, radiation and heat transfer change in ways that standard fire curves do not capture, creating a serious gap in current testing methods. The conversation emphasised that performance-based engineering must consider the entire fire timeline, not only the period of fully-developed fire.

You can listen to the full podcast episode (#218) HERE and explore Andrea’s related research papers here:

• Defining the fire decay and the cooling phase of post-flashover compartment fires
• Thermal characterisation of the cooling phase of post-flashover compartment fires

The Fire Science Show is produced by Fire Science Media in collaboration with OFR Consultants.