A five-alarm Bronx fire that killed two people on Tuesday afternoon spread quickly because multiple doors were left open, according to the FDNY.

FDNY officials said firefighters arrived just minutes after the flames broke out at the five-story apartment building on East 187th Street in Belmont. They found heavy smoke and fire on all floors of the building, according to officials. The FDNY said an ongoing investigation found multiple doors in the building were left open, including the one to the apartment where fire marshals believe the fire started.

“Door was left open to the fire apartment, door was left open to the front of the building, and the door was left open to the bulkhead, which is the exit to the roof,” FDNY First Deputy Commissioner Daniel Flynn said at a press briefing Friday morning. “If not for those doors being open, we believe that the fire may have even been contained in that one apartment, and we would have not, not had lost anybody.”

Officials also said people in the Bronx building did not use the building’s fire escapes, and that the building’s door was propped open. On Thursday, they urged New Yorkers to ensure they always close the door behind them in the event of a fire, and also ensure their windows are not blocked and that they can access their fire escapes.

“ Walk out onto the fire escape, show your children where the fire escapes are. Do not get caught off guard when these fires occur,” Flynn said. “Always know how you're going to escape.”

Flynn said the two victims of Tuesday’s fire were found in the stairwell, and said they were making their way down from higher floors.

It’s been an active week for the FDNY. On Thursday, firefighters responded to a five-alarm fire at a church in Queens. And on Friday, an impound lot in Brooklyn went up in flames, destroying cars parked there, ABC News reported. No injuries were reported in those fires.