The fire began in a couch on a porch early Saturday morning and spread through four rowhouses.
Some neighborhood residents have charged that firefighters took as long as half an hour to reach the scene. Several people were arrested Monday at a large protest.
The city released 911 tapes and other records this week that showed a ladder truck arrived at 2:48 a.m., a minute after it was dispatched and about three minutes after the first call to 911 reporting the fire.
"You cannot get there quicker than a minute," Sawyer said at a news conference Tuesday. "That's not humanly possible. You're asking our heroes to be superheroes."
Jeff Boone, a neighbor who made the first call, said he tried to put out the fire in the couch himself before calling 911.
"It was pure chaos," he told the Philadelphia Daily News on Tuesday.
The four children, 4-year-old twins Maria and Marialla Bowah, Patrick Sanyeah, 4, and Taj Jacque, 1-month, are all from Liberian-American families.
Liberian Ambassador Jeremiah Sulunteh visited the fire scene Tuesday evening with Rep. Bob Brady, D-Pa.
"I want answers, because this did not just happen to these families," Sulunteh told neighborhood residents at a meeting at Christ International Baptist Church. "This did not just happen to Southwest Philadelphia. This could happen anywhere. We need to know how to keep our children safe."
Philadelphia-born rapper Meek Mill also visited the block Tuesday.