In the aftermath of the catastrophic wildfires that swept through California in 2023, a structural engineer from Sonoma County has designed and constructed a network of fire-proof bunkers capable of withstanding temperatures exceeding 1,000 degrees Celsius. The project, initially a personal response to the loss of her own home, has now attracted the attention of British civil engineers who see potential applications for climate resilience in the United Kingdom.
Dr. Elena Marchetti, a materials scientist by training, spent two years developing what she calls the "Phoenix Shelter." The bunkers are constructed from a composite of reinforced concrete and aerogel insulation, a material originally developed for NASA space suits. Aerogel, which is 99.8% air, provides exceptional thermal resistance while being lightweight enough to be prefabricated and transported to remote locations. The shelters are buried partially underground and feature a ventilation system that filters out smoke and particulate matter, powered by a solar array. Each unit can accommodate a family of four for up to 72 hours, with emergency supplies including oxygen tanks and fire-resistant suits.
The impetus for Marchetti’s work was personal. In 2020, the Glass Fire destroyed her home in Kenwood, a small town nestled in the Mayacamas Mountains. She lost everything except the clothes she was wearing. "I realised that traditional evacuation routes could be cut off in minutes," she told the Guardian. "The fire front moves faster than a car can travel on a winding road. I needed a solution that allowed people to shelter in place."
The bunker design has since been tested by the California Department of Forestry and Fire Protection (Cal Fire) in controlled burn experiments. The shelter’s exterior temperatures reached 1,100 degrees Celsius during a four-hour test, while interior temperatures remained below 28 degrees Celsius. Data from these tests have been published in the journal Fire Technology and have caught the eye of engineers at the UK’s Institution of Civil Engineers (ICE).
Dr. James Whitfield, a civil engineer specialising in extreme events at the University of Cambridge, is leading a study to adapt the Phoenix Shelter for UK conditions. "While we don’t face the same scale of wildfires as California, climate change is increasing the risk of heatwaves and droughts in southern England," he said. "The aerogel insulation and passive cooling systems could be invaluable for protecting vulnerable populations during heatwaves, which already kill more people in the UK than any other natural hazard."
The research team is particularly interested in the bunker’s use of phase-change materials (PCMs) embedded in the walls. These materials absorb thermal energy as they melt, acting as a heat sink. In the UK context, they could be used to stabilise internal temperatures during heatwaves without requiring air conditioning. The team also sees potential for the shelters to serve as emergency cooling centres in urban areas, retrofitted into existing basements or community centres.
The shift in focus from fire to heat reflects a broader recalibration of climate adaptation strategies. The UK’s Climate Change Committee has warned that by 2050, summers like 2022’s record heatwave could occur every other year. The current building stock, designed for a temperate maritime climate, is ill-equipped to handle these extremes. Marchetti’s design, while born of fire, may offer a template for resilience against heat.
Marchetti herself is cautious about the export of her design. "I built these bunkers for one reason: to give people a fighting chance in a fire. If they can help in other ways, that’s wonderful. But the priority must be preventing the conditions that make such shelters necessary," she says. Her next project is a fire-resistant building material made from recycled agricultural waste, which she hopes will reduce the vulnerability of existing homes.
The UK study is expected to conclude in early 2026, with a pilot project in Cambridgeshire or East Anglia, regions most susceptible to drought and heat. Whitfield acknowledges that the psychological barrier of "bunkering down" must be overcome. "In the UK, we think of basements as damp and dark. This design is about creating a safe, comfortable space that feels like a natural part of the home."
As global temperatures continue to rise, the line between adaptation and survival blurs. Marchetti’s bunkers are a stark reminder that climate change is not a future abstraction but a present reality demanding concrete solutions. For the engineers studying them in Cambridge, they represent not just a refuge from fire, but a blueprint for a changing world.
