Understand the fire performance trade-offs of using low-carbon "green" concrete. New university research provides crucial data on the increased risk of explosive spalling in common eco-friendly concrete mixes.. Fire Induced Spalling in Low Carbon Concrete: Understanding the Risks The construction industry's shift towards more sustainable materials has brought significant environmental benefits, yet new research highlights potential fire safety trade offs. A recent study, conducted by a prominent UK university and published in a peer reviewed journal in late 2026, delves into the fire performance of low carbon concrete, specifically examining its susceptibility to explosive spalling. This research is critical for fire engineers, responsible persons, and accountable persons navigating the complexities of modern building design and material selection. While the drive for 'green' concrete is commendable, a thorough understanding of its behaviour under fire conditions is paramount to ensure the continued safety of occupants and the structural integrity of buildings. This article unpacks the findings, their implications, and the necessary considerations for those involved in fire safety and building design in the UK. The Challenge of Sustainable Concrete and Fire Safety The drive to reduce the carbon footprint of construction has led to the widespread adoption of supplementary cementitious materials (SCMs) such as Ground Granulated Blast furnace Slag (GGBS) and pulverised fuel ash (PFA), commonly known as fly ash. These materials partially replace ordinary Portland cement (OPC), significantly lowering embodied carbon. However, their inclusion alters the concrete's microstructure and thermal properties. The university's research specifically investigated concrete mixes with high percentages of GGBS and fly ash, simulating realistic fire scenarios. Historically, concrete has been lauded for its inherent fire resistance, contributing to compartmentation and structural stability during a fire event. This new data compels a re evaluation of assumptions surrounding these newer, more environmentally friendly formulations, ensuring that sustainability goals do not inadvertently compromise fire safety provisions outlined in documents like Approved Document B (ADB) of the Building Regulations. Quantifying the Increased Risk of Explosive Spalling The study's key finding is a quantifiable increase in the propensity for explosive spalling in concrete mixes incorporating high levels of GGBS or fly ash when exposed to elevated temperatures. Explosive spalling is the violent fracturing and detachment of concrete from the surface of a structural element, exposing the reinforcement and accelerating structural degradation. The research employed advanced fire testing techniques, subjecting various concrete formulations to standard fire curves. The results indicate that the altered pore structure and thermal conductivity of low carbon concrete contribute to a more rapid build up of pore pressure, which is the primary mechanism behind explosive spalling. This phenomenon can severely compromise the fire resistance period of structural elements, potentially leading to premature collapse and hindering safe evacuation, directly impacting the obligations under the Regulatory Reform (Fire Safety) Order 2005 (RRO 2005). Mechanisms Behind Enhanced Spalling The research elucidated several factors contributing to the heightened spalling risk. Firstly, the denser microstructure often associated with SCM rich concretes can trap moisture more effectively, leading to a faster and more intense build up of steam pressure internally when heated. Secondly, differences in thermal expansion coefficients between the various constituents within the concrete matrix, particularly at high temperatures, can induce additional stresses. Thirdly, the modified chemical composition can affect the concrete's ability to resist tensile stresses generated by thermal gradients. These combined effects create a scenario where low carbon concrete, despite its environmental credentials, may have a reduced capacity to withstand the thermal shock and sustained heating characteristic of a developing fire, posing challenges for achieving the performance criteria set out in standards like BS 9991 and BS 9999 for fire safety in architectural and structural design. Implications for Responsible and Accountable Persons The findings have direct and significant implications for Responsible Persons (as defined by the RRO 2005) and Accountable Persons (under the Building Safety Act 2022). Their duties include ensuring the safety of occupants and compliance with fire safety legislation throughout a building's lifecycle. Where low carbon concrete has been specified or used, a thorough understanding of its fire performance characteristics becomes crucial. This necessitates: Review of Fire Strategies: Existing fire strategies for buildings constructed with such materials may require reasses