The explosion on Lillian Ngoyi Street (previously Bree Street) last month was caused by methane gas, according to the City of Johannesburg.
Officials from the city briefed the media in Braamfontein on the latest explosion results.
While the type of gas has been confirmed, the source of the gas is still being investigated, according to the report.
According to city manager Floyd Brink, the gas did not come from Egoli Gas pipelines.
“Only post-explosion has been confirmed on the timeline of the Egoli gas system so what we have done in this regard we send in a team of independent specialists from our side as the City,” he said on Wednesday.