The blast happened on Thursday afternoon at 213 North Fulton Street.
In a statement issued on Friday, utility company UGI said crews from contractor Great Western were working on a cast-iron main replacement project before the explosion.
UGI said it responded immediately after the blast and found no gas leaks in the immediate incident area, in the street or around the house.
UGI said the cast-iron main was not a factor in the explosion and there are no issues with UGI facilities serving North Fulton Street.
The house at 213 North Fulton took the brunt of the blast - its glass shattered and much of the front porch buckled.
The four people injured included two residents and two workers for a utility contractor.
Allentown residents are sensitive to natural gas line safety issues. Just last February, only blocks away, a massive natural gas blast killed five people.
