Mr. Brosnan, San Mateo County Coroner Robert Foucrault told The Almanac, died as a result of "inhalation of products of combustion," by which he said he meant soot and superheated air.
Firefighters found Mr. Brosnan lying next to a deflated air mattress in a first-floor bedroom in the one unburned part of the house. He may have tried to stand up, encountered superheated air, taken a breath and died, his lungs seared from the heat, Menlo Park Fire Protection District Chief Harold Schapelhouman said.
"One breath and it'll kill you right away," Mr. Foucrault said.
The fire was a furious one, Chief Schapelhouman said at the scene later that day. He noted the absence of a roof and supporting beams and the blackened, skeletal, spindly uprights — studs that, unlike today's lumber, actually measured 2 inches by 4 inches. (The house was built in the 1920s or 1930s, he said.)
"That's really unusual, to see that depth of burn," he added, pointing to what firefighters call "alligator" charring for its scale-like surface texture. "There's nothing (left) there. That's a long time in burning. ... It could have been preheating for hours. I'd say this fire was burning for maybe 30 minutes before anybody discovered (it)."
It was a very hot fire, too, the chief said, pointing out how it had blistered paint on a neighboring garage and blackened a redwood tree and fence. The home's melted aluminum window frames meant a temperature of at least 1,000 degrees, he said.
Because the fire had a head start and a high potential for injury, firefighters fought it from the outside, he said.
"Every fireman wants to go to a fire until you deal with something like this," he said, referring to the fatality. "All of a sudden, you're sort of brought up to the reality of what your job is."
The fire appears to have started accidentally, Chief Schapelhouman said. The blaze was reported at about 1:30 a.m. at 825 Berkeley Ave. in a tree-filled neighborhood.
Firefighters arrived within four minutes and quickly extinguished the flames, Chief Schapelhouman said. The fire was under control by 2 a.m.
Peter Farmer, who lives next door, said Mr. Brosnan rented the house for the past six or seven years and lived alone.
Mr. Farmer was sleeping when he, his wife and their two daughters awoke to the sound of explosions, looked out the window and saw flames pouring from the house next door.
"The flames were intense and probably reaching up 30 or 40 feet," Mr. Farmer said. "It was quite frightening to wake up and see the house completely in flames."
Chief Schapelhouman said the explosions were propane cylinders and aerosol cans that were kept in a wooden shack behind the burning home.
Bay City News Service contributed to this report.