Linesense™ Comes To The Rescue

Diesel Multiple Units (DMUs) powered by underfloor diesel engines served as the workhorses of British Rail for decades. Because passengers sat directly above these engines, robust fire detection and suppression systems were vital for safety.

Legacy Fire System Challenge

As a heritage 1960 vehicle with legacy fire systems, restoration of our Class 108 DMU presented us with a challenge.

The original fire detection system wrapped around the engine used a pyrotechnic component.

In the presence of a flame, this component triggered an explosion to close an alarm circuit in the driver's cab, instantly shutting down the engine and flooding the bay with Halon gas.

While Halon rapidly smothers chemical and electrical fires without leaving residue, it was identified some time ago as a major culprit in depleting the ozone layer.

Following the 1989 Montreal Protocol, Halon was banned and the gas bottles were removed.

Today, on heritage units, train staff rely on portable extinguishers to put out any fires manually.

In addition to the missing Halon systems, the original pyrotechnic detection components are deteriorating and pose unnecessary risks during routine maintenance.

Heat-Sensitive Digital Cable Solution

To modernise the system safely, the PWRS sought to source a modern replacement: a digital heat-detection wire manufactured by Linesense™.

How it Works

The wire consists of a twisted pair of conductors insulated from each other.

If a fire or extreme heat occurs, the outer insulation melts at a precise pre-set temperature, bringing the two wires together to trigger the driver's alarm system.

Overcoming the Sourcing Hurdle

Implementing the modification required an updated electrical wiring diagram sourced from the First Generation DMU Group and 10 metres of the specialised Linesense™ twisted-pair cable.

However, we hit an obstacle. The wire is very expensive and normally sold only in large commercial reels far exceeding our 10 metre requirement.

This is where Joshua Risk of Linesense™ stepped in:

• He initially contacted regular commercial customers to see if any had a 10 metre offcut left over from previous jobs.
• When that yielded no results, he conducted a stock check and located a drum with 30 metres remaining.
• Then he arranged for the cable to be delivered free of charge.

Project Completion

Thanks to the generosity of Joshua Risk and Linesense™, the PWRS has now successfully completed the fire detection system modifications on both engines of our Class 108 DMU.

The society is eternally grateful for their support in ensuring our DMU will run safely when it re-enters service.

Geoff Ogden
PWRS