Worldwide interest in Joburg CBD explosion from cities, engineers

There has been worldwide interest in the recent explosion in Johannesburg's CBD, with the investigating team being “inundated” with questions and requests for information from engineers and city officials from around the world.

Mayor Kabelo Gwamanda said he established a technical team, led by city manager Floyd Brink, to implement a detailed and advanced investigation into the explosion and the responses required from the city. 

 The investigation is being conducted by consultant and civil engineer Johan Lagrange. The team includes highly experienced engineers, gas specialists, technologists and academics who have worked tirelessly to ensure that they conduct a rigorous investigation into the possible causes of the explosion. 

“The team has been inundated with a number of enquiries from cities and engineers across the globe who follow closely such incidents. There is international interest to understand the causes of the explosion and to build knowledge about such incidents as they occur across the globe,” Gwamanda said.

“This has placed us under pressure to ensure that the team that investigates is the best in the space and that the outcomes of our investigation are credible and backed by science and evidence,” Gwamanda said.

The methane gas which caused an explosion on Lilian Ngoyi (formerly Bree) Street may have originated from a slow leak of natural gas into the tunnel.

The gas may have originated from the downstream outfall sewer system on the west side of the site or from underlying Archaean geological layers that escaped to the surface due to seismic action. 

This is the latest development in the investigation into the cause of the explosion that left one person dead and 48 others injured.

Lagrange said on Wednesday during a presentation on the latest findings that an Egoli Gas supply to the area has been isolated and the inflow of gas post-explosion into the tunnel appears to have stopped.

He said the main supply will not be connected again as confirmed by Egoli Gas in writing.

The preliminary assessments revealed that during the explosion, two northern lanes of Lilian Ngoyi Street were lifted and then collapsed into an underlying service channel in which the explosion is believed to have occurred.

Water, sewer, stormwater, electricity, and gas services were damaged, either directly due to the explosion or because of the collapse of the road.

Telecommunication services were also damaged. The explosion happened inside an electricity services tunnel underneath Lilian Ngoyi Street. 

The fuel was methane gas that infiltrated the tunnel at a point lower than or in the explosion site and travelled up until it got trapped at the tunnel crest near Von Brandis Street and filed back down.

Brink said investigations ruled out  any terrorist action, or zama zamas [illegal miners], cable theft or foul play.

“It was not an Egoli Gas pipeline explosion or pipe rupture nor a large leak before the explosion, only post-explosion as confirmed on the timeline of the Egoli Gas SCADA [supervisory control and data acquisition] monitor,” he said.

He added that there was no negligence by any department or any intentional action by individuals or intentional release of gas into the tunnel. “No signs of people living in the tunnels nor recent cable theft were found,” he added.

Brink said the estimated cost for repairs was R178m but that might change once the municipality receives detailed designs for the entire project.

Gwamanda said the team was now fully engaged as part of its response and recovery process in devising means to test and monitor the presence of various gases in their underground tunnels.

He said the team will provide the city with plans to ensure such incidents don't happen again.

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