Tunnel vision

ACO Technologies says being in a tunnel when fire strikes can be terrifying – but what if the safety measures bring secondary safety issues of their own?

Transport tunnels are always at risk of vehicle fires, and the enclosed space has the potential to trap people and hinder the response of emergency services. It is prudent for these tunnels to have fire and smoke detection systems linked to sprinklers for an immediate response. However, automatic sprinklers can cause flooding, and the drainage systems needed to prevent that can also operate as shafts for the fire to spread. One solution is to build a drainage system that can mitigate the risks of both hazards.

An example of this is Silvertown Tunnel in London, which opened in April 2025 as a ‘Significant Infrastructure Project’ that would ease congestion in central London and lower journey times by up to 20 minutes. The tunnel connects Silvertown with the Greenwich Peninsula and is a twin-bore tunnel with two parallel tunnels. ACO Technologies was tasked with building a new drainage system that would mitigate both fire and flood risks, using its KerbDrain components.

Before the new drainage system was built, hydraulic analysis was carried out to make sure each drainage unit could manage the volume of water released by the sprinkler system. This is a key part of designing infrastructure, including drainage networks, and involves assessing the behaviour and performance of water.

To reduce the risk of flooding from the sprinkler system, kerb drainage was placed along one side of each tunnel, with gully outlets every 15 metres. This meets the Transport for London (TfL) specification of 50mm inlet diameters or less, while preventing blockages from debris.

What is key is that the drainage system also has a bespoke flame trap to prevent fires spreading. A U-bend was built between the gullies and carrier pipe so that the pipes in the drainage system are always partially filled with water. This will stop fires from spreading through the drainage system.

The flame trap is constructed from stainless steel components and uses a custom spigot (a device that manages the flow of liquid) to join iron pipes with stainless steel pipes.

Heavy loads

Partway through the project, ACO Technologies installed expansion joints at interfaces in the tunnel to allow for movement without disrupting the drainage system. The new joints were designed and tested to accommodate 20mm of horizontal and 16mm of vertical movement, all while withstanding the force of a ten-tonne lorry. 

The joints are robust stainless-steel units anchored on each side of the drain. They were rigorously tested to EN1433 standards. This includes:

• a ten-tonne accidental wheel loading test in accordance with the design manual for roads and bridges specifications; and
• EN 1433 Load Class D400, which is a drainage system designed to withstand the weight of vehicles up to 40 tonnes driving over it.

Two flexible 100mm polypropylene pipes were positioned behind the stainless steel cover of each unit to make sure water is carried across the joints effectively. Now all TfL needs to worry about is the smooth flow of traffic. 

Further reading
ACO Technologies: aco.co.uk
Behaviour and management of water: b.link/DB_hydraulic

Image credit | Alamy