Methane gas caused Joburg CBD blast, say city officials

The 19 July explosion, which tore up 450 metres of Johannesburg’s Lilian Ngoyi Street (formerly Bree Street), sending taxis and cars flying, killing 34-year-old Joseph Dumisane and injuring 48 others, was caused by methane gas.

This was confirmed by city officials during a media briefing on Wednesday after much speculation over the cause of the blast.

Johan la Grange, a civil engineer and city consultant, explained that the explosion was fuelled by methane gas that infiltrated a tunnel beneath the road “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”.

Executive Mayor of Johannesburg Kabelo Gwamanda with his MMCs during an oversight visit to Lilian Ngoyi Street on 24 July 2023. (Photo: Gallo Images / Luba Lesolle)

The city had commissioned an independent service provider to conduct a probe into the explosion. The report was delivered on Wednesday, but it is yet to be tabled in council before being released to the public.

La Grange identified three possible sources of where the methane gas originated:

1. A slow leak of natural ingress into the tunnel.


2. Methane gas originating from downstream outfall sewer systems, west of the incident site.


3. Methane gas from underlying Archaean geological layers escaped to the surface due to seismic action.

La Grange said explosions of this nature were common across the globe. He linked the explosion to minor seismic activity on the day of the incident, and an earthquake earlier in the week.

“These incidents happen all over the world. In 1969 it happened in New York where six blocks were blown up. This year, it happened in Venezuela… it happened in China.”

Johannesburg Water employees at work on 25 July 2023 after the 19 July gas explosion. (Photo: Leon Sadiki)

At the time of the explosion, a gas line leak was suspected to be the primary cause. Gas lines run beneath the pavement, but not under the road itself. Egoli Gas, which manages the municipal lines, said its lines operate at low pressure and were unlikely to cause an explosion.

The company later announced the detection of a small leak, but it maintained it was unlikely to be the cause of the explosion. The city has since confirmed that Egoli Gas was not responsible for the blast.

“It takes three or four things to happen to create a perfect storm, and that’s why we had this incident,” said La Grange.

Read more in Daily Maverick: City of Joburg confirms gas caused deadly explosion, but can’t say from where

It was suggested the blast could not have been caused by gas because no flames were seen during or after the event. City manager Floyd Brink explained that this had been a low-level explosion.

“As we flew… our drones into those tunnels, we could not pick up any indication of black scorch from a fire,” said Brink.

Reconstruction costs

To deal with the aftermath of the explosion, city officials, led by Mayor Kabelo Gwamanda, said they expected to spend no less than R173-million to reconstruct Lilian Ngoyi Street.

The city has already spent about R4-million on procuring technology such as drones, the services of professional experts and providing temporary relief services including water tankers and ablution facilities.

Read more in Daily Maverick: ‘I felt my intestines go cold from fear’ — Joburg residents describe blast scene chaos

After the explosion, the city revealed that it had gas pipelines running parallel to water lines in its underground tunnels.

To avoid a recurrence of similar incidents, Brink said: “The tunnel design will be upgraded based on current international codes for tunnels to reduce the risk and severity of explosions.

“We will also introduce continuous gas detection and alarms and gas detector sensor monitors for all staff working the tunnels regularly.”

State of disaster

On 26 July, officials indicated they were working on a process to declare the gas explosion a disaster, a move which would unlock resources for the rehabilitation of the road and tunnels.

“The declaration of the disaster is critical in order to allow us to assess the impact of the explosion on infrastructure and to cost the rehabilitation work required,” Brink said a week ago.

“We have mandated the Disaster Management Centre to commence with the processes and to finalise a report for submission to the [Provincial Disaster Management Committee] within the next seven days.”

A week later, the explosion still hasn’t been declared a disaster. Probed on the delay, Brink said the paperwork was being finalised.

Skills gap

The city employs more than 40,000 people, but its engineering teams have been depleted through years of cadre deployment, which has continued under the coalition governments that now run the city, Daily Maverick has reported.

Read more in Daily Maverick: Johannesburg’s emergency call for engineers, gas-detection experts after CBD explosion exposes dire skills gap

Brink, however, dismissed allegations that the city had no internal capacity to deal with disasters such as the explosion.

“I find these to be misguided and misinformed for the emergency we had to deal with. During such an emergency, highly specialised technical skills are required and the additional technical support and assistance [that] can be leveraged from the private sector and/or industry is standard practice.”

Despite the city being in financial distress and the council in political turmoil, Gwamanda echoed Brink’s sentiments that the city was functional and had a competent administration.

“In this case, the city manager and technical team have indeed displayed the best of Johannesburg and have proved that the city is stable and functional,” said Gwamanda.

Asked how long reconstruction would take, Brink said, “We can guarantee you it will not be 18 months. We’ve got a clear interest as a city to show what we can do in a short space of time.” DM