About 4,500 calls failed to get through during a six-hour Washington state 911 outage last week, CenturyLink said Monday.
Elaborating on an explanation it offered Friday, the telecommunications company said the outage was caused by a technical error in a third-party vendor's call router, which prevented the system from properly processing calls.
In one case early Thursday, an Everett, Wash., woman said she made 37 calls about an intruder breaking into her home and had to drive him away herself with a knife.
The problem did not involve the computer bug known as "Heartbleed," nor any malfunction in CenturyLink's network, the Monroe, La., company said in a statement.
"CenturyLink and its vendor partner have taken steps to implement an enhanced monitoring process and have addressed the router issue," the company said.
CenturyLink has not identified the vendor.
Dispatchers were deeply troubled by the outage and the Washington Emergency Management Division also wanted an explanation. Emergency Management spokeswoman Wendy Freitag did not immediately return a call for comment left after business hours Monday.
The outage lasted from 12:36 a.m. until 6:26 a.m., the company said, adding that about 770 calls to 911 were completed in that period. The outage involved 127 public safety answering points in Washington, while other answering points successfully rerouted calls.
"We are working closely with our vendor partner to fully to understand this outage," Brian Stading, CenturyLink Inc.'s Northwest region president, said in the statement. "At this time, we are confident that the 911 system is fully operational and stable."
A similar outage in parts of northwest Oregon lasted more than two hours early Thursday. CenturyLink said that was caused by a maintenance issue. The Oregon outage affected about 16,000 phone customers in Lincoln, Tillamook and Yamhill counties.
Kurt Mills at the SNOPAC center in Everett that dispatches for three dozen police and fire agencies called the Washington state outage shocking. He said the failure, especially the Everett woman's experience, distressed his dispatchers.
"I've worked throughout the country for 25 years, and I have never seen anything like this, never— for a whole state to go down," he said last week.