The incident started around 12:30 a.m. Thursday when PG&E crews were doing routine inspections of their gas lines when they detected a leak. They were trying to reach that situation when they accidentally hit a line carrying nitrogen gas.
The nitrogen line serves 12 high-tech companies in the area that use the gas in their cleaning process.
"If there was enough of it and it built up enough in concentration, it would displace the oxygen and it's an asphyxiant. Eventually we would succumb to that," says Capt. Steve Alvarado from the San Jose Fire Department.
In this situation, the inert gas did not pose a health threat. The drill that hit the nitro line was left in, acting as a cork to cap the leak until a full repair is made. The question is, how did the accident happen in the first place? PG&E is looking into that.
"We take pride in doing everything safely and correctly and so we'll do a thorough investigation into what happened in this case and take corrective action," says PG&E spokesperson Brian Swanson.
If you look at any street where digging is scheduled, there's a roadmap of what lies beneath the surface.
"There's all kind of utilities, there's storm lines, sewer lines, fiber optic lines, gas lines," says Dan Davis of Devcon Construction.
To find out what lies where, any company or person with a dig operation must call USA, or Utility Service Alert, 72 hours before a job starts.
"All of their members go out and mark their facilities and then everything will proceed with relative safety," says Timm Borden, the deputy director of San Jose Public Works.
The markings must be put in place within 48 hours and have a color code. Blue denotes a water line. Red is electrical. Orange is any communications line and yellow is a clear warning of a gas line, whether it's fuel, natural or nitro.
"So you did have USA markings?" asks ABC7's Karina Rusk.
"Well we were working on our gas lines and so we were familiar with where our gas lines existed but unfortunately there was this natural gas line directly underneath the asphalt," says PG&E spokesperson Brian Swanson.
There are questions about whether PG&E followed all of its procedures. There are also questions about whether the nitrogen gas line was not buried far enough beneath the asphalt. All of that will be looked at in the investigation.