The NTSB provided updates regarding the investigation into Thursday’s house explosion near Hayward on Saturday. Investigators visited the site of the explosion on Friday morning. On Saturday, the National Transportation Safety Board reported their investigation found that the ¾ -inch diameter steel line and the 2-inch diameter steel gas main in the vicinity of the accident were installed in the 1940s. The NTSB also confirmed the natural gas pipeline was damaged during grading work associated with a road improvement project along the street in front of the home. According to preliminary information from PGE, on Thursday, a third-party contractor unaffiliated with the company was doing work in the area when it notified the utility that its workers struck an underground gas line at about 7:35 a.m. Hayward Dec 12 NTSB investigating explosion near Hayward that injured 6, levelled buildings Hayward Dec 11 6 injured, buildings damaged in explosion near Hayward PGE then dispatched crews to the scene and found two releases of gas. Authorities said the crews shut off one at 8:18 a.m., and the other at 9:25 a.m. Authorities reported the explosion happened 10 minutes later, injuring six people, including three PGE workers, and levelling multiple buildings. The NTSB said investigators will remain on the scene for the next five to seven days, and they will be doing the following: The damaged natural gas pipeline will be tested, exposed, and evidence will be collected.  A detailed timeline of events leading up to the explosion, including the timing of the damage and notifications of the damage will be developed.  Several workers from the construction project, as well as PGE employees and first responders will be interviewed.  Gas facility and One-call records, as well as construction practices will be reviewed. NTBS informed that a preliminary report will be available on their website, and can be accessed by searching the pipeline investigations pages. However, they added that the probable cause of the explosion, along with any contributing factors, will be detailed in the final report, expected to be completed in 12 to 24 months.   ...read more read less