FDNY urges NYC residents to keep apartment doors closed in the event of a fire. Here's why.

Fire officials say the deadly Inwood fire earlier this week followed an all-too-similar pattern -- flames spreading through open doors.

As a result, the FDNY is now getting the word out to keep doors closed, demonstrating Thursday how easily fire can spread when a door is left open.

The difference between life and death

The contrast during the department's presentation was apparent in the aftermath of Monday's fire in Inwood that killed three people. One apartment, which was charred black, had an open door, while its neighbor closed their front door.

"This is what happens. As you can see, fire spread in the stairway and roof as well," FDNY First Deputy Commissioner Dan Flynn said.

Authorities say open doors also fueled last month's fire in the Bronx that killed two people.

"If not for an open door, I'm confident no one would have died in either fire," Flynn said.

Nakayla Moreno, 19, was killed in the Bronx fire. Family members said her boyfriend tried to break a window for them to escape.

"Unfortunately, when he was trying to get the window open, he couldn't see her anymore. It was completely black smoke," said Tiara Sessoms, the victim's aunt.

What New York City law says  

Across the five boroughs, apartment doors are required by law to swing closed and latch by themselves after being opened.

The city has issued 52,000 violations over self-closing doors so far this year, compared to nearly 59,000 violations issued by this time last year.

"We certainly encourage building owners to abide by that law and make sure those doors are closing. Unfortunately, a lot of times those doors are self-closing and occupants make changes in the apartment that limit ability for the door to close," Flynn said.

The Department of Housing Preservation and Development told CBS News New York that the Inwood apartment from Monday's fire currently has three open violations regarding self-closing doors, and was actually enrolled back in January into an HPD program that targets buildings with multiple code violations and closely monitors that they're making repairs.

As for the Bronx apartment, it did not have any active self-closing door violations, but FDNY sources said a resident had propped a door open to allow their cat to escape.