More than one hundred schools and education settings in the United Kingdom have been closed due to concerns over the integrity of concrete roof panels. So far, 147 schools are known to contain reinforced autoclaved aerated concrete (Raac), with approximately one hundred fully or partially closed, impacting more than 100,000 students at the start of the new school year.

The latest developments began in August when a Raac panel collapsed in a school in England, prompting a wider government review. While 147 schools have been identified as containing Raac, education unions warn that “hundreds more” schools could be impacted. Meanwhile, thirteen universities have closed or partially closed, alongside a number of theaters and cultural venues that have closed as inspections continue. The Guardian additionally reports that the number of UK prisons containing Raac may take two years to identify.

Raac, also referred to as “aircrete,” was utilized from the 1950s to the 1990s in UK public buildings. Developed to be lighter and more economical than traditional concrete, Raac is injected with air during construction to create air bubbles, resulting in a structure twice as light as standard concrete. However, the material is more vulnerable to moisture, water, and rebar corrosion, meaning regular maintenance and inspection are required.

“Recent evidence shows that the behavior of these panels can no longer be predicted reliably due to uncertainties in the material and the mechanical properties of the panels, which are highly impacted by deterioration,” explains Juan Sagaseta, Reader in Structural Robustness at the UK’s University of Surrey. “This is simply because the panels have been used so far beyond their intended design life and in many cases without proper maintenance.”

The crisis has sparked a wider criticism about the maintenance of public buildings in the United Kingdom. The national government has been accused of previously making substantial cuts to funding for school rebuilding, with The Guardian reporting that one in seven schools in the Raac list were previously denied urgent government funding. Hospital conditions have also come under scrutiny, with NHS England noting that hospitals regularly have to shut units due to dilapidation.