Cadent collaboration helps OptoSci Ltd innovative sensing technology

Getting to the bottom of gas escapes under our busy roads can be a challenge at the best of times. But when gas finds its way into underground utility ducts carrying essential services such as electricity and telecoms cables it can prove a real headache for Britain’s gas distribution networks.

However, there could literally be light at the end of the tunnel. A collaborative project  between Cadent – Britain’s biggest gas distribution network, Northern Gas Networks, Wales & West Utilities and OptoSci Ltd is trialling fibre optic sensing technology to tackle the problem.

“Once gas finds its way into ducts it can travel long distances in different directions, making it difficult to trace the source of the escape. Up to three quarters of the time fixing the escape can be spent tracing its source,” says Adam Hassall of Cadent.

“It’s a particular problem in city streets congested with utilities and ducts. Traditional methods of tracing gas in ducts can result in multiple excavations and take several days, leading to traffic congestion and higher manpower and reinstatement costs. By utilising this technology we aim to ensure that disruption to our customers is kept to an absolute minimum.”

Over the last four years the networks and OptoSci Ltd, a leading producer of optoelectronic systems, have been developing OptoMole.

“OptoMole uses a novel combination of laser-based gas sensing technology and fibre optics to tackle the gas in ducts problem. Low power laser light is transmitted from a compact control unit (which contains all the electrical system elements) through a long, tough fibre-optic cable to a small, all-optical, inherently safe gas probe at the end,.

“This probe is inserted into and moved along the duct, immediately detecting any methane present and instantaneously transmitting the data back to the control unit. The profile of methane in the duct is displayed at the control unit, with the highest gas concentrations pinpointing where gas is entering the duct,” explains Adam.

OptoMole builds on OptoSci’s existing multipoint gas monitoring technology (based on Tuneable Diode Laser Spectroscopy) used to detect methane over long distances in coal mines and service tunnels. However, developing OptoMole was no mean feat, as Dr Douglas Walsh, Director and General Manager of OptoSci, explains.

“We had to convert a system of fixed sensors and a large, office-based control unit into something small, durable and portable.

“To fit in the confined space of a duct, the sensor had to be miniaturised whilst retaining the quality of light transmission. It also had to withstand mud and water and there could be no electrical components in the sensor because of the risk of igniting gas.

“Furthermore, the control unit had to be shrunk to the size of a brief case to ease handling and storage in the service vehicle. We overcame these issues by using a variety of novel system design techniques.”

“It has been something of a departure for us,” admits Dr Walsh, “we wouldn’t have come up with this application had we not been approached by the gas distribution networks.”

Field trials of the device are now in their final stage. OptoMole units are being used on live gas escapes on a daily basis by Cadent, Northern Gas Networks and Wales & West Utilities

Initial results have been promising. Some trials have demonstrated a 30% – 60% cost saving compared to traditional methods. Most of the savings have come from reduced staff time, fewer excavations and lower traffic management costs.

Reducing disruption to the public has been another benefit of the technology.

“Our trials in Manchester have seen some jobs that would have taken to two days reduced to less than four hours, resulting in a better experience for our customers and the local community,” says Adam.

Feedback from the trial will demonstrate the level of operative training required and identify any final technical tweaks needed to make OptoMole a ‘business-as-usual’ tool for all the gas networks.


  • No major excavation work required. This minimises disruption and cuts costs.
  • Improving how we identify leaks supports the integrity, safety and reliability of the network.
  • Safer for the public and our workforce, with reduced methane emissions and no spark risk.