The storm water attenuation crate fire hazard

We are aware of the consequences of vehicles catching fire on roads and in single level and multi-storey car parks.  Here is a new problem making an appearance – the collapse of the ground level car park.

Plastics stored or used in the open air, within or on buildings can be a recognised fire risk and actions are taken to reduce that risk, but what about the plastics used underground?

It seems to me that there is a new fire risk associated with the use of plastic storm water attenuation crates underground that has not yet been recognised or considered.

In America these plastic crates have been used to create a large underground storm water storage facility.  The containment was then covered and used as a car park.   Recently (2024) those crates caught fire, the fire could not be extinguished and the car park deck collapsed.  There is a short YouTube video here with more videos being added.

As for the cause of the fire – I have some ideas but cannot tell you what the precise cause of the fire was.  In my opinion the cause of the fire is irrelevant. What I can say is that the authorities failed to recognise the risk of the installed crates burning under the ground.  This sounds like a Grenfell Tower chapter to me.  Today we are using increasing quantities of crates for residential and civil engineering projects.  I think there is a need to have a close look at the current legislation on where, when and how these crates (and other plastic products) are used.  We should have alarm bells ringing urgently here! Are these load bearing plastic crates really a safe and sustainable solution with an appropriate design life?

Extract from Google – In the UK’s Sustainable Drainage Systems (SuDS), plastic crates, also known as attenuation or soakaway crates, are used for underground storm water management. They temporarily store excess rainwater during heavy rainfall, forming modular, high void ratios to release the water slowly back into the ground or drainage system. This prevents [?]flooding, eases strain on sewer systems, and mimics natural drainage processes, fulfilling regulatory requirements for SuDS in England and Wales.

How Plastic Crates Work in SuDS
1. Storage: Crates are modular plastic units designed to store large volumes of water underground.
2. Controlled Release: The stored water is then released slowly into the ground or a controlled outlet, such as a sewer or watercourse.
3. Mimic Natural Processes: This process aims to mimic how natural landscapes would absorb and process rainwater, preventing rapid runoff.
Key Functions and Benefits
Flood Prevention: By temporarily holding excess water, crates reduce peak flow rates and prevent [?] localized flooding.
Reduce Sewer Strain: They alleviate pressure on overburdened public sewer systems during heavy storms.
Groundwater Recharge: The controlled release allows for some water to infiltrate the ground, helping to recharge groundwater levels.
Space Efficiency: The high void ratios (over 95%) of plastic crates maximize water storage in a relatively small underground footprint.
Durability and Strength: Made from strong, recycled polypropylene, they are designed to withstand vehicular loads, making them suitable for installation under car parks, roads, and other paved surfaces.
Regulatory Context
Plastic crates are a key component of SuDS in the UK.
SuDS, including crates, are mandatory under UK planning regulations to manage surface water runoff sustainably, especially in urban areas with many impermeable surfaces.
In England, SuDS became mandatory for new developments from 2024.
In essence, plastic SuDS crates are a sustainable, engineered solution that uses modular plastic structures to effectively manage storm water, preventing flooding [?] and supporting greener urban development by working with natural water processes.

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