This is the soakaway/attenuation crate fire hazard problem. It is counter-intuitive but today, we are burying structural forms of inflammable plastics in the ground to create water storage and attenuation voids. We are expecting these plastics to be safe simply because they are buried and may also be wet. HOW WRONG WE ARE! Just search for the Williamsburg Premium Outlets fire in November 2024 and see what can happen.
More than a year after an underground fire collapsed a parking lot behind the Williamsburg Premium Outlets, the site remains a gaping crater with little sign of progress.
Firefighters determined the fire originated in the drainage system — in a series of plastic crates stacked in blocks to form a holding tank (beneath the gravel and asphalt parking lot) that allows for temporary storm-water storage until it can drain off slowly. Something caused a fire – the plastic material burnt – and then the car park collapsed. Please be warned.
This sounds like the Grenfell Tower cladding fire rating saga.
END