Joburg CBD disaster a 'pure gas' explosion but gas source yet to be determined

The blast on Lillian Ngoyi (formerly Bree) Street in the Johannesburg CBD on Wednesday was a “pure gas explosion”.

This was confirmed by a consultant and civil engineer leading the investigation into the cause of the explosion that left one person dead and 48 others injured.

Johan Lagrange dismissed speculation the explosion could have been caused by zama zamas or that it was an act of terrorism.

“It is a big explosion; it is not a 5l gas [bottle] by zama zamas or something like that. I haven't seen traces [of it being] ... a terrorist attack.

“There is no evidence of that at all. We mustn't even discuss it, this is a pure gas explosion,” he said. 

The City of Johannesburg deployed technologies and drones in the underground tunnels to investigate the cause of the explosion.

Lagrange was talking during a technical media briefing in Braamfontein on Friday along with city manager Floyd Brink.

“The ignition was accidental, and the cause of the gas explosion was the gas that leaked. The source of the gas is what we are trying to determine — whether it is an old gas line, whether it is from the tenant side or the client side,” he said.

He added that he brought in a specialist on Friday who has been doing explosion simulations to determine the magnitude and size so they could try to determine the volume that was exposed and other sources they should be searching for.

“We are busy with that. We do not conclusively know where it came from. What it is we are quite sure of is what caused it. It is 450m [deep] and about 7 metres wide, about 169,000 tonnes of material that was lifted ... I can tell you it is a lot. 

“We will be able to give you figures in about three or four days' time, once we have done the calculations,” he said. 

He said they have gathered visual evidence inside the tunnels and there was nobody living in them as there is a lot of water.

“[There is also] no evidence of any people working down there so we exclude that in totality,” said Lagrange.

He said buildings close to the epicentre of the explosion were safe and there was no indication that buildings or foundations had been damaged.”

Brink said the Johannesburg EMS had completed an assessment of the area between Lilian Ngoyi and Loveday streets.

It was discovered that the tunnel's structural integrity was “deformed” and unstable and could collapse as a result of the movement of cars crossing towards the CJ Cronje building.

“This area has now also been barricaded for the safety of motorists and pedestrians.

“We wish to caution residents to in no way interfere with the boundaries and to not enter the cordoned-off areas for the sole purpose of their safety,” said Brink.

He said they were concerned that gas might be trapped in subsoil cavities such as basements in the area.

“As per our commitment yesterday [Friday], we have since inspected a total of nine buildings in the area and our test results at this stage are negative. We have struggled with access to one building, and we will finalise the test once we have gained access,” he said.

He added that all the Egoli Gas valves had been closed and technical teams had given an assurance that they are were isolating the area from their system.

Brink said positive pressure ventilation fans had been deployed to blow out any gas remnants that may have remained in the underground system. Extraction of gas in the atmosphere was also under way. 

“Again, these are intrinsically safe methods being deployed to ensure the safety of residents. We are beginning to see a decrease in the presence of the gas and should be in a position to safely allow for the restoration of power and other services by Monday at the latest,” he said.

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