FIRE DEPARTMENT investigators have determined the cause of a terrifying explosion that leveled three rowhouses in South Philly on July 29.

A natural-gas leak inside 428 Daly St. was ignited when a contractor attempted to light a cigarette, Fire Department Executive Chief William Dell said yesterday.

The contractor, Steven Barrientos, suffered second- and third-degree burns in the blast, which injured seven others and destroyed the two neighboring properties.

Barrientos "still suffers considerable pain and regularly sees his rehabilitation and physical therapists for treatment," said Stephan Rosenfeld, a spokesman for Saltz Mongeluzzi Barrett & Bendesky, the law firm that represents the injured worker.

The rowhouse was purchased in January by SCK Investments, which completely renovated the property.

A civil lawsuit was filed against SCK shortly after the explosion on behalf of neighbor Sekeya Fields and her 15-year-old daughter, Shaquorie. The teen was trapped in the rubble of her family's home at 430 Daly for at least 30 minutes after the blast.

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