OLYMPIA — The Washington state Emergency Management Division believes the 911 system is stable now, but it still wants assurances from CenturyLink there won’t be a repeat of last week’s statewide outage, Division Director Robert Ezelle said.

The telephone company shared information Monday as it investigates what went wrong, he said.

“We’re encouraged by the information they provided,” Ezell said Tuesday. “We’re trying to pin down what the root causes were and why backups didn’t pick up when a component failed.”

CenturyLink says about 4,500 calls failed to get through during a six-hour outage on Thursday that was caused by a technical error in a third-party vendor’s call router. About 770 calls were completed in that period. CenturyLink says it has addressed the issue.

The outage involved 127 dispatch points in Washington.

The company said a similar two-hour 911 outage in parts of northwest Oregon was caused by a separate problem.

The vendor involved is Longmont, Colo., based Intrado Inc., which manages the 911 database for CenturyLink.

Intrado issued a statement Tuesday from Ray Wendell, senior director, corporate communications, saying: “Intrado has partnered with CenturyLink in the State of Washington for nearly 20 years to provide 911 services. Public and personal safety are at the heart of Intrado’s business, and we take any service disruption very seriously. The service disruption on April 10th was caused by an isolated system issue that was promptly resolved after root cause identification. The system is stable and continues to process 911 calls normally.”

One woman who futilely called 911 early Thursday remained in a Tacoma hospital Tuesday after repeatedly passing out, possibly because of a heart condition.

Carla Adams says she collapsed at her Tacoma apartment after 1 a.m. Thursday and when she awoke she called 911 without success from one phone for six or seven times.

“I couldn’t understand why it was failing,” she said. “I thought something was wrong with my phone.”

She crawled across her floor to another phone and tried another half-dozen calls to 911.

She finally called a son in San Diego who somehow was able to get paramedics to respond to her room about 15 minutes later. She was treated for cuts and bruises to her face from hitting a night stand. She also has other medical conditions.

Adams said she has heard newcasts that few people were affected by the outage. “Well, I’m one,” she said.