Dive Brief:

• Fire investigators trying to determine what started huge blazes that razed Houston and San Francisco residential projects under construction valued at a total of $277 million say welding is their most likely suspect at this point.
• The fires, a week apart, started shortly after the end of the workday in San Francisco and in early afternoon in Houston, and wind whipped the Houston fire through that building very quickly.
• Finding the causes means digging through the stories of buildings that are now piles of rubble and interviewing workers. A ruling will likely be some time coming – if investigators can even establish what happened.

Dive Insight:

In the Houston fire, officials said they had reports of welders working on the roof before the fire started, and video recordings of the fire showed it burning heaviest in the top floor before working its way down. The National Fire Protection Association said that windy-day welding should include a fire-watcher with the welder to keep track of slag and sparks.