By Lehlohonolo Lehana.
City of Johannesburg says the investigation in the inner-city explosion had been completed, with methane gas identified as the cause.
City manager, Floyd Brink, announced the findings at a press briefing in the mayor’s boardroom on Wednesday.
“The delivery of this report marks the end of the immediate response work we reported on previous and paves the way to our medium interventions which will include the restoration and repair work, “said Brink.
He explained that there was a 5-15% threshold for an explosion, and in explaining why there was no fire, he said the threshold was not above 15%.
Civil engineer and city of Joburg consultant Johan La Grange said at a low level, methane gas was explosive.
La Grange said it was not unusual and that there had been another two similar explosions around the world this year.
He said there was global interest in the blast as people were looking to learn from the event and what corrections had been made.
La Grange said that at 15:00 on the day of the blast, there was a small seismic activity, and earlier in the week, there had been an earthquake that was believed to have released the gas from the lower tunnels.
He said the explosion site was where the gas travelled to the highest point of the tunnels and the spark was still being investigated.
Brink said the immediate response from the city was now coming to an end and they had so far spent R4 million on professional services, cordoning off the area and the temporary provision of water, ablution services and food.
The city said last week it was looking to declare a local disaster after the explosion.
Brink said the city would require about R178 million, which could rise, to repair the road, reconstruct the tunnel and fix other damaged infrastructure.
He said a team of specialists in fire with experience in industrial explosions and gas systems, fire dynamics and explosion simulation specialist engineers, explosions, gas and fire dynamics specialists, structural, geotechnical, electrical and civil engineers, forensic specialists and occupational health and safety professionals had worked around the clock as part of the team on the CBD explosion.
Brink could not give an exact timeline but said the road would be fixed in less than 18 months.
The 90-year-old tunnels underneath inner-city Johannesburg will now be upgraded according to the relevant international codes and South African standards.
New safety measures will include continuous gas detection and alarms, while the tunnel’s structure will be reinforced to withstand a 9.5% methane explosion.