SAN ANTONIO — Workers with CPS Energy and the National Transportation Safety Board excavated a yard in San Antonio's Preston Hollow neighborhood on Friday morning, three days after two blasts demolished homes on the street. Officials with both agencies did not provide comments on the investigation.

The two blasts occurred about two hours apart on Tuesday night and drew a large emergency response. The houses on either side of one remaining home were destroyed.

Several neighbors said at a Thursday meeting that they were told a tree in a backyard was related to the incident. A crew from McCoy Tree Surgery arrived at the site within an hour to remove the tree, hauling branches of an oak into the drainage channel south of the home.

On Friday morning, workers wearing NTSB and CPS Energy clothing dug in the yard using an excavator and shovels, stopping periodically to take photographs of the dig. They used a battery-powered saw to cut and remove what appeared to be a large section of tree root. Many of the people involved in the dig left the area after the root was removed, and work in the yard was scaled back on Friday afternoon.

Parts of Preston Hollow Street remained closed to vehicle traffic, and a few residents in the blast area were still without utility service on Friday afternoon. CPS Energy reported on Thursday that electric and gas services in the restored area were clear and safe. The utility urged anyone who found debris or damage to their homes to contact its Customer Response Unit, and said personnel would be available at the Northeast Senior Center at 4135 Thousand Oaks Drive from 8:30 a.m. through 5 p.m. until Sunday, April 26.

The number to call at any time for suspected gas leaks is 210-353-HELP (4357) or 911. On its website, CPS Energy advised residents who suspect a gas leak to leave the area immediately and not try to find the leak, to avoid sparks by not operating light switches, telephones, garage doors or vehicles, to call 911 and the utility to report the leak, and to leave gas meter valves to authorized personnel.

The NTSB said its investigations involve three primary areas: human factors, the pipeline system, and the operating environment. The agency said it had no plans to conduct interviews or hold media briefings.