The State Fire Marshal's Office and Rockland’s fire and police departments have concluded their investigation into the 666 Main Street apartment building fire on March 17.

Mary-Ann MacMaster, of the State Fire Marshal's Office, changed the initial cause of the fire from "Undetermined" to "Accidental" after the investigation indicated the fire began in a canister vacuum cleaner in a hallway.

An occupant had just finished using the vacuum and placed it in the hall before leaving the apartment to run errands. At the time she left, there was no indication of any issue with the cleaner; shortly thereafter, however, other building tenants noted the interconnected smoke alarms began to sound.

“Unfortunately, these tenants, seeing no issue in their immediate units, assumed the problem was an error in another unit, and did not investigate further until another 10-15 minutes had passed,” according to an April 1 news release from the city of Rockland. “At that time an odor of smoke was apparent in the apartment directly above the fire. From there the fire was quickly discovered and the tenants were able to alert all the building occupants and get them to safely evacuate.”

One resident said she had to pass through smoke as she exited the building.

The Rockland Fire Department emphasizes several key safety points learned from the fire:

1) Smoke alarm activations must be treated as if there is a real fire. While it is human nature to seek the cause of the alarm, ensure the safety of all people first, before looking to find a fire, as in some cases, upon discovery the fire could affect safe egress.

In many buildings smoke alarms are interconnected and can indicate the problem is elsewhere in the building. And if frequent false alarms occur seek better detectors, detector locations or alternatives, but do not removes or ignore the alarms because they truly are lifesaving equipment.

2) All powered equipment, despite built-in safety features, can be a source of ignition.

With vacuums it is important to remove the contents or bags whenever they are full. Some indications that something may need to be addressed is a reduction in vacuum suction efficiency and/or a change in the sound of the unit.

Use caution when vacuuming. Ashtrays, fireplaces and wood stoves can have tiny hot spots that aren't seen but are easily hot enough to light the contents of a vacuum bag or canister.

3) Close doors and minimize openings.

The occupants at 666 Main Street did right by opening the apartment to ensure anyone inside was not trapped or otherwise in need of help, but upon leaving the doorway, the door was left open, the investigators said.

“This is a relatively new priority for the fire service so a lot of education is needed to change prior practices,” the city said, in its release. “In most cases an open door will allow a smoldering fire the necessary oxygen to grow, thus any time we can minimize the amount of available oxygen to a fire we should. This means keeping doors to as many rooms as practical closed as often as practical. And upon discovery of a fire compartmentalizing it by closing doors as you're exiting is one of the ways to minimize fire growth and property damage. All of these things should only be done when it safe to do so, better that we routinely keep areas compartmentalized so that upon being alerted to a fire the focus is on getting everyone out safely.”