Photo By AP Wideworld
A March 25 Houston fire, similar to a San Francisco blaze a week earlier, destroyed an apartment complex under construction. In each case, investigators are looking at welding as a possible ignition source.

Fire investigators in Houston and San Francisco are going through rubble and interviewing workers on-site at a pair of under-construction apartment complexes that ended up in ashes.

One factor common to both sites is the possibility a jobsite welding spark ignited the fires.

"We won't have any information for several weeks," says Jay Evans, Houston Fire Dept. spokesman. "Five floors were leveled, so it's going to take quite a bit of digging."

Earlier, Deputy Chief Greg Lewis told reporters, "There was a report of a couple of guys on the roof doing welding."

The March 25 fire, fueled by 20-mph winds, destroyed the $50-million, 396-unit Axis Apartments complex in Houston. Dallas-based developer and builder JLB Partners of Dallas did not return multiple calls and emails. The company has not had any OSHA violations during the past five years.

Wind was not a factor in the San Francisco fire on the "fairly calm afternoon" of March 12, says Mindy Talmadge, San Francisco Fire Dept. spokeswoman.

But "the fire created its own winds," endangering neighbor buildings, she says.

That five-alarm fire was reported after most construction workers had left for the day, and San Francisco Fire Chief Joanne Hayes-White told reporters that some "torch work" had been under way.

The 360-unit, $227-million building is being developed by BRE Properties and built by Suffolk Construction. Suffolk did not respond to multiple calls for comment. OSHA has fined the company almost $54,000 for 13 serious violations since 2009, most of them involving fall-protection issues.

Windy days like the one in Houston call for a fire watcher along with a welder, says Guy Colonna, division manager with the National Fire Protection Association.

"They can monitor if slag or sparks go great distances, like the third floor to below or [winds carrying] sparks a great distance," Colonna says.