The company said the incident cut off its power supply from Pacific Gas & Electric to one of its Internet Data Centers in Sunnyvale, Calif. Its backup generators failed to take over, leading to an outage that lasted for about an hour, beginning at 2:50 p.m. PDT.
The outage was unrelated to rolling blackouts ordered later in the day by the California Independent System Operator (CAISO), keeper of the state's power grid.
"Service was interrupted at one of the Exodus Communications Internet Data Centers (IDCs) in Sunnyvale, Calif., for approximately 60 minutes due to the interruption of commercial power supply from Pacific Gas & Electric resulting from a PG&E underground vault explosion," Exodus said in a statement Tuesday.
The company referred questions about the explosion to PG&E, which could not be immediately reached for comment.
The outage affected Web portal Yahoo and some other Exodus customers. Yahoo's instant messaging service, for example, was unavailable for much of the afternoon. The service was restored by 6:45 p.m. PDT.
"Due to a power outage at one of Exodus Communications' Internet Data Centers yesterday, the accessibility of a few Yahoo services was affected, including Yahoo Messenger," Yahoo spokeswoman Shannon Stubo said in a statement Tuesday. "Services returned to normal in approximately three hours."
The comments clarified Yahoo's statement Monday that the outage stemmed from statewide power shortages.
Exodus said it is investigating the failure of its backup systems.
"Although each Exodus IDC is equipped with (uninterruptible power supply) systems and backup diesel generators to sustain operations during a utility power interruption, the operations at the affected Exodus IDC failed to automatically roll over to the backup generators," the company said in its statement. "Exodus engineers are performing a root cause analysis to determine why the IDC operations did not roll over to the backup generators and to prevent such occurrences in the future."
For years, Yahoo had hosted many of its services with GlobalCenter, the Web hosting unit of communications carrier Global Crossing. But Exodus acquired GlobalCenter earlier this year.
The incident at Exodus occurred hours before California power regulators instigated rolling blackouts statewide.
California has been suffering from power shortages since early this year, leading regulators to call for conservation and rolling blackouts. Tight electricity supplies and high demand led to two days of rolling blackouts Jan. 17 and Jan. 18 in Northern California and statewide blackouts March 19 and March 20.
On Monday, CAISO implemented a Stage 1 emergency notice at 8:04 a.m. PDT, indicating that demand was likely to outstrip supply. The emergency was upgraded to Stage 3, the highest level, at 5:01 p.m. PDT. For 32 consecutive days earlier this year, California was in Stage 3 emergencies because of a lack of energy resources.
Outages affecting Internet service have not been limited to California. AOL Time Warner's America Online in April blamed a brief service interruption on a power outage affecting Northern Virginia.
News.com's Gwendolyn Mariano contributed to this report.