A flare-up fueled by a broken window caused the deaths of two firefighters in a Diamond Heights house fire last year, and not procedural errors, San Francisco fire officials said today.

An internal safety investigation on the June 2, 2011 fire at 133 Berkeley Way released today indicates that firefighters Lt. Vincent A. Perez and Firefighter Paramedic Anthony M. Valerio were killed by extremely high temperatures of up to 700 degrees caused by a sudden flare up, known as a flashover.

The intense fire event, which lasted several minutes, was caused when a window shattered in the room where the fire started, sending a rush of oxygen to the flames, according to the report. The heat was drawn up a stairwell from a below ground-level floor, where the fire began, to the ground-level floor where Valerio and Perez were standing.

“They were caught in a chimney,” said Assistant Chief David Franklin, who worked on the team that prepared the report.

The report describes a number of errors and communication problems at the scene and makes recommendations for how the handling of future incidents can be improved. But fire officials said the flashover was not something that could have easily been prevented or predicted.

“What Vincent and Tony did is exactly what all of us would have done,” said Fire Chief Joanne Hayes-White, noting that it is standard practice in the department to make an aggressive attack and try to get water on a fire as quickly as possible. “The key factor was something that we really had no control over.”

Valerio and Perez, whose Engine 26 was the first to arrive on scene after the fire was reported at 10:45 a.m., were trying to reach the seemingly small, routine fire through the front door of the four-story wood-framed home, which was built into a hillside with floors both above and below ground level. They conferred with other firefighters arriving on the scene on the ground floor at 10:53 a.m., and agreed that the fire was below them, the report said.

A short time later, around 10:58 a.m., the flashover occurred and drove back other firefighters who were attempting to enter the building through the garage.

Firefighters were ultimately able to put out the fire through a lower-level entrance on the side of the building. Perez and Valerio were discovered on the ground floor at the top of the stairwell somewhere around 11:04 a.m. or 11:05 a.m., after failing to respond to several radio calls, officials said.

At no time did the two firefighters send out any distress calls or trigger their emergency alarms, officials said. The last radio transmission from Engine 26 came at 10:52 a.m., when they said “we’re still looking for it, zero visibility, more to follow,” the report said.

The two men suffered internal and external burns to 40 percent of their bodies, and died of “thermal injuries,” according to the San Francisco Medical Examiner. Perez died at the hospital later the same day, and Valerio died two days later.

Two other firefighters were also treated and released for injuries incurred in the fire.

Hayes-White said the department is developing a risk assessment policy to help determine how to approach fires, particularly in difficult situations such as that presented by the multi-level home.

While fire protection gear worn by the firefighters appears to have functioned as designed during the flashover, their radios were severely damaged by the intense heat.

Hayes-White said the department has since learned that there are no national standards for the radios.

“We’re very concerned about it and believe this will be a national issue,” Hayes-White said.

The state Division of Occupational Safety and Health issued several citations to the department in November with fines of up to $21,000 for violations related to the June 2 fire. The violations included a failure to maintain sufficient contact and communication among employees.

However, Hayes-White said today that none of the Cal-OSHA violations were related to the deaths of Perez and Valerio. She said the department has appealed the citations and believes they will be reduced.

The report also found that the response to the fire, caused by an electrical short, was delayed by an attempt by the residents to put it out themselves. Hayes-White urged residents to call 911 right away so that professionals can respond promptly.

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