That's when he heard a neighbor's plea: Would someone help with the baby?
He said he dashed across the street and took the newborn from the man's arms as he cleared the building.
Moments later, emergency crews arrived and rushed nine people, most more dazed than badly injured, to hospitals. One man - a contractor working alone in the vacant building - was seriously burned when the house at 428 Daly St. exploded as he tried to light a gas hot-water heater, fire officials said.
"Everything we ever owned is all gone," said Fields' mother, Sekeya, 38, dragging on a cigarette outside a temporary shelter for evacuees of the blast that leveled the rowhouse in a neighborhood known to some as Lovely.
The explosion at 11:09 a.m. sheared away walls of two adjacent rowhouses, crushed parked cars under tons of spilled bricks, and displaced people from 70 homes on Daly and Wolf Street.
Property records show permits were issued for 428 Daly in April for a major renovation, including the installation of a furnace and an air-conditioning system.
The house was bought in March by SCK Investments L.L.C., according to the deed.
Efforts to reach the owner were unsuccessful.
Mayor Nutter's office said the fire marshal, Department of Licenses and Inspections, and Philadelphia Gas Works were investigating the cause of the natural gas leak.
Witnesses said the explosion caused overhead wires to fall and spark. The Fire Department extinguished a small fire and rescued several people from the debris.
Most of the wounded were taken to Jefferson University Hospital with minor injuries. The contractor working in the basement was taken to the Hospital of the University of Pennsylvania with severe burns. He was later transferred to Temple University Hospital in critical condition.
The Red Cross of Southeastern Pennsylvania set up a temporary shelter at Taggert School, and said 14 people spent most of the day and early evening there.
The organization said last night it was continuing to help six families with food, clothing, and shelter. Three families were staying at Red Cross House.
The center could stay open if needed to provide shelter for people left homeless by the blast.
All residents of the affected homes were accounted for, city officials said.
The Fire Department used listening devices Monday afternoon to ensure that no one was left in the building. L&I brought in heavy equipment to begin the cleanup.
Smoke alarms were still beeping in the wreckage Monday evening.
The fire marshal was collecting a list of missing pets and planned to bring any animals it found to the shelter. Sekeya Fields said her cat, Miss Molly, might still be in the rubble.
PGW spokeswoman Melanie McCottrey said there had been no reports of gas leaks from that neighborhood in recent days.
"We have no record of anyone calling in, no one in that area," she said.
Judy Delisi, who lives on the block, said she smelled gas about five minutes before the explosion, and went to her basement to check.
She was sitting down when there was "just a big ka-boom."
"It shook," Delisi said. "You knew something fell."
She ran outside to find a debris cloud rolling down the street.
Residents said the explosion and collapse reminded them of an earthquake and reported that firefighters arrived quickly. A firehouse is nearby at Fourth and Snyder.
Victor Masella, who owns Michael's Deli & Grocery on Wolf, was startled by the rumbling.
"The whole foundation shook," said Masella, whose store shares an alleyway with the damaged houses.
Nearly 50 residents of the block crowded into his deli in shock and confusion.
Tishon Jones, 21, was taking a nap in his home at Fourth and Daly when he awoke to find his bed shaking.
He made his way downstairs as a police officer banged on his door and told him to leave. As he stepped outside, the air carried a strong odor of gas. He saw a cloud of smoke and debris outside a house that had collapsed.
"It looked," he said, "like it was a bomb."
As neighbors fled, Jones looked down the block and saw a man running into the street screaming, his arm on fire.
Neighbors rushed toward the burning man with bottles of water and tried to douse the flames. Rescue workers moved in and took the man to a waiting ambulance.
Quang Lac said the door to his South View Pizza at 367 Durfor St. opened and then slammed shut at the blast's concussive power.
First he suspected explosives. Then he saw flames.
He learned only later that a gas explosion caused what seemed like a scene out of a disaster movie in Lovely.
Contact Michael Matza at 215-854-2541, firstname.lastname@example.org, of follow on Twitter @MichaelMatza1
Inquirer staff writers Sulaiman Abdur-Rahman, Edward Colimore, Martha Woodall, Bob Warner, and Robert Moran contributed to this article.