The explosion did break a water main, and the heat was so intense that it cracked the windshields of fire engines.
It took first responders about half an hour to pinpoint the cause of the massive fireball.
Firefighters, with the help of residents, dragged hoses from 4,000 feet away to supply water.
Many of the officers and firefighters who responded to the explosion acted despite the danger. Many were fighting to save the neighborhood they grew up in.
The 54-year-old pipeline was not equipped with an automatic shut off valve. PG&E said it took two hours and 46 minutes to manually cut off the gas, because it wasn't safe for workers to go near the blaze.
However, investigators said the shutoff valves were at least a mile away.
A lab in Washington, D.C,. will examine a 28-foot long section of the pipeline to determine if the explosion was caused by a small leak or a catastrophic failure.
Four people were killed, three others have not been found and 37 homes were destroyed.
Gov. Arnold Schwarzenegger, who is just back from Asia, toured the neighborhood Wednesday.
PG&E said it will set aside $100 million to help residents rebuild. Also, state and federal lawmakers have called on PG&E to upgrade any other pipelines in heavily populated areas that now can only be closed down by hand.
Also, the Obama administration is seeking tighter oversight of the nation's pipelines and stronger penalties for violations of pipeline safety rules. The legislation was submitted to Congress Wednesday by Transportation Secretary Ray LaHood.
If you would like to help the residents affected by the San Bruno fire, monetary donations can be sent to:
American Red Cross Bay Area Chapter
85 Second Street, 8th Floor
San Francisco, CA 94105
You can also call (888) 4-HELP-BAY or visit the American Red Cross Bay Area Chapter's website to donate online, http://www.redcrossbayarea.org.
The Associated Press contributed to this report.