Montgomery County Fire and Rescue Services said an alert neighbor walking her dog on Monday banged on the front door of a Potomac home just in time to alert two teenagers inside to the flames engulfing the back of the home.

Firefighters were dispatched to the 12400 block of Willow Green Court in Potomac just after 4 p.m. on Monday and found a heavy fire that has left the two teenagers and two others displaced.

The neighbor smelled smoke and found flames in the back of the house, called 911, tied her dog to a nearby mailbox, ran back to the home and pounded on the front door to alert any occupants, according to a MCFRS press release. The teens inside narrowly escaped the fire, MCFRS said, and officials are crediting her with helping them escape safely.

MCFRS investigators determined the fire was accidental and was sparked by cooking materials that had been placed outside to cool. Because of the more than $600,000 in damage to the home, investigators were unable to determine if the home had smoke alarms.

One firefighter suffered non-life threatening injuries at the scene and has been released. About 80 fire rescue personnel responded to the scene, as did the American Red Cross to assist the displaced family.

Photos via Rockville Volunteer Fire Department