A man injured in an Oak Street apartment fire Friday has been downgraded to serious condition.

Gerald Sanford, 53, was reported in satisfactory condition Monday at Maine Medical Center, where he is being treated. 

Fire crews were called to 23 Oak St. for report of an explosion and arrived to find Sanford outside the building suffering from smoke inhalation and facial burns, Brunswick Fire Chief Ken Brillant said Friday. Sanford had been helped outside by someone else in the building, according to witnesses.

Brunswick, Topsham and Freeport firefighters quickly extinguished the fire, which was contained to Sanford’s upstairs apartment.

Brunswick Deputy Fire Chief Donald Koslosky said Wednesday that investigators don’t know if there was an explosion, but that the fire was caused by a cigarette and was oxygen-fed. 

Investigators don’t yet know whether the cigarette fell into the couch or spontaneously ignited, and what role the oxygen played, Koslosky said, due to the extent of damage in the apartment. 

He confirmed there was an oxygen device in the apartment as well as multiple oxygen bottles.

Fire and rescue workers found Sanford had some superficial burns on one side, but were most concerned about the smoke inhalation he’d suffered, which can cause damage to the lungs, especially for anyone with compromised lungs. 

No one else was injured and other tenants were allowed back in the building that night, with the exception of the tenants of the apartment below Sanford’s, which sustained water damage. 

Koslosky said oxygen itself is not flammable but it does promote combustion, and allows things to ignite more quickly and burn with more intensity. 

For this reason, he said, people should not smoke around oxygen.