On Wednesday, the city woke up to a nightmare, but it cannot be called unimaginable.

Philadelphia’s deadliest single residential fire in at least a century consumed a three-story rowhouse at 869 North 23rd St. in Fairmount. The blaze took the Philadelphia Fire Department nearly an hour to place under control. At least 12 people, including eight children, were killed.

“This is without a doubt one of the most tragic days in our city’s history,” Mayor Jim Kenney said during a news conference at the scene hours after the blaze.

“This punches you in the gut,” added City Council President Darrell L. Clarke, whose district includes the block where the fire occurred. “Children. People in the community. It’s just tragic. I don’t know what to say. It’s so sad.”

The death of the most vulnerable Philadelphians is harrowing, but with so much loss occurring in our city on a daily basis, it is anything but unimaginable. The fire on North 23rd Street might have started around 6:30 a.m. Wednesday — but the injustices that made the blaze so catastrophic were long in the making — and are the story of families all over Philadelphia grasping for a place to live.

The two-unit rowhouse was owned by the Philadelphia Housing Authority and at least 26 people called it home — overcrowding that Deputy Fire Commissioner Craig Murphy called “a tremendous amount of people.” The Housing Authority told The Inquirer that 15 people were living in a single unit of the building as of last year.

At least four smoke detectors in the building were not working and there were no fire escapes on the upper floors, according to officials.

» READ MORE: What we know and don’t know about the Fairmount house fire

It wasn’t that long ago when Philadelphia experienced the pain of a similar calamity barely a mile away from 23rd Street. In March 2018, a fire in a makeshift affordable housing development on 1855 N. 21st St., killed four people including 3-year-old Haashim Johnson. The building was zoned as a single-family home, but the residents lived in small apartments — finding shelter where possible in a city with a significant shortage of affordable units.

Again, an overcrowded house. Again, safety hazards and potential code violations. Again, the poorest Philadelphians are the victims. Again, children paying the ultimate price of the ongoing housing crisis in the poorest large city in the richest nation.

It is essential that what comes next is a swift, thorough, and public investigation — both into what caused the fire and into the overcrowded housing conditions that drove the death toll.

It’s also critical that the Housing Authority provide a full accounting of its inspection routines, occupancy regulations, and the resources it needs to provide not only housing to more people but more adequate housing to the tenants it serves.

The fire in Fairmount needs to be a wake-up call about the living conditions of Philadelphians — a city in which an estimated half of rental units are unlicensed, meaning that there is no way to know if they are up to code and safe for habitation.

» READ MORE: ‘Only babies’: After Fairmount fire, Philadelphia mourns an unthinkable loss

Wednesday’s fire should also serve as a reminder of the unrelenting levels of resilience that Philadelphians — particularly Black Philadelphians — are forced to endure. Yes, a dozen people died in a fire. On a typical Wednesday over the last year, at least three people have died of overdoses and one or two others were murdered. And that does not begin to take into account the daily death toll from COVID-19. All told, it is an unbearable level of loss.

And still our community has come together in recent days to strengthen one another, to exhibit brotherly love and sisterly affection with whatever reserves of energy one can muster after a day like Wednesday. Those who are able can do their part to help by donating to local fund-raisers — such as through Children First PA, a Philadelphia-based child advocacy nonprofit. It is also vital that we remain vigilant in our demand for answers and change in the weeks and months to come — that we say loudly and clearly that the bleak reality that so many Philadelphians experience every day is unacceptable.

In the aftermath of this fire, our city mourns. But the time is now for public officials to start the hard work of making sure that a tragedy like this never, ever happens in Philadelphia again. Dismissing a fire that killed at least a dozen people as a grim but unavoidable accident would be a disservice to the victims in Fairmount — and to any person in Philadelphia who is going to sleep tonight in an unsafe house.