* Victim succumbs, others struggle from toxic smoke
* Doctors say more could develop respiratory problems
SAO PAULO, Feb 1 (Reuters) - A 20-year-old woman late Thursday succumbed to injuries from the nightclub fire in the southern Brazilian college town of Santa Maria, pushing the death toll from the disaster last weekend up to 236.
Civil defense authorities in Rio Grande do Sul, the state where Santa Maria is located, said the victim suffered a heart attack while struggling with injuries that included burns on more than half her body.
An additional 126 people remain hospitalized after the fire, which was caused by an outdoor flare lit by a musician performing at the Kiss nightclub. The flare, investigators say, ignited overhead soundproofing, a synthetic foam that burned and within minutes spread toxic fumes throughout the venue.
Most of the victims died after inhaling the fumes, investigators concluded on Thursday.
Many of those in nearby hospitals, more than half of whom are on respirators, have developed scorched airways and pneumonia-like complications from the poisonous vapors. Authorities fear more survivors could become sick because of the fumes, noting that the onset of symptoms could be gradual.
Police this week detained two owners of the club and two band members as they look into safety violations including the use of the flare, which was banned for indoor use, and faulty fire extinguishers, exit signs, and blocked access to the club's only exit.
The factors led to a stampede that crushed some of the victims and kept others from fleeing the fumes and flames.
Police have not yet charged any of the four detainees, but have said at minimum they are likely to face manslaughter charges.
Local prosecutors are also investigating city and fire officials to determine if they were negligent in allowing the club to remain open despite the safety violations. (Reporting by Daniela Ades; Writing by Paulo Prada; Editing by Vicki Allen)