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SGS released a tracer gas inside the tunnel and measured it at various set points so the gas dispersion was modelled. The gas used was sulphur hexafluoride as it’s colourless, odourless, can be reliably detected in small concentration and isn’t commonly used, minimising background interferences.

Cityscape at Niight

Approached by a Melbourne consultant, SGS was engaged to map air flows through the M5 tunnel in Sydney.

One of the challenges encountered in this process, was creating a method that analysed air samples for sulphur hexafluoride down to PPT (parts per trillion) level. At the time, no Australian lab could reach the detection limits required for the study. To combat this, the project team adopted some slight modifications to a gas chromatographer so it could easily detect 10 ppb in the air samples.

This meant the client only needed to release a few litres of gas in the tunnel for its diffusion to be detected and mapped over several kilometres.

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About SGS

SGS is the world's leading inspection, verification, testing and certification company. We are recognised as the global benchmark for quality and integrity. With more than 89,000 employees, we operate a network of more than 2,600 offices and laboratories around the world.