The suit claims that PGW, the city-owned utility, failed to maintain and replace a network of aging pipes.
The City of Philadelphia and two local plumbing contractors - Bart Emanuel & Son Plumbing and Heating, Inc. and Lepore Plumbing, Inc., are also named in the lawsuit.
Brian Diu, 28, and another man were killed when a leaking gas pipe exploded on December 19, 2019.
SEE ALSO: Likely cause of fatal South Philadelphia explosion, fire was natural gas leak: Officials
"The defendants' conduct was reprehensible and is indefensible," said Steven G. Wigrizer, who is representing the Diu family. "The incredibly close-knit Diu family remains in shock at the loss of Brian and fears for the lives of others throughout Philadelphia whose gas service is provided by PGW. They've asked us to do all we can to make PGW's historically unsafe system - responsible for death and destruction- safe, once and for all."
Five homes along the 1400 block of South 8th Street were destroyed.
PGW declined to comment but says it invests $85 million each year into infrastructure.