Mary Shepler, the chief nursing officer at EvergreenHealth, which includes the hospital in Kirkland, defended the facility’s preparedness and protocols. The hospital, she said, has adequate supplies, including single-use masks and face shields that are sterilized and reused.

The hospital, too, has conducted drills and training for such situations, Ms. Shepler said, adding that she understands the stress that people are under while dealing with a new virus.

“It’s uncomfortable to all of us in this new zone,” she said.

Ms. Shepler said that after quarantining some workers who were exposed to coronavirus patients, the hospital determined that the extent of the quarantine was unrealistic because it left shortages in a needed work force. They brought nurses back who were asymptomatic — an approach deemed reasonable by the C.D.C., she said — and are testing them twice a shift. They are also required to wear masks while treating patients.

The California Nurses Association, a statewide union that has grown into the largest organization of nurses in the country, with representation of 155,000 nurses, is scheduled to hold a news conference on Thursday afternoon to demand access to “the highest level of protection” for nurses on the front lines. It also plans to demand training and clear plans for how to handle patients suspected of having the virus.

“Employers shall plan for a surge of patients with possible or confirmed Covid-19, including plans to isolate, cohort, and to provide safe staffing,” the union said in a statement. “Any nurse/health care worker who is exposed to Covid-19 will be placed on precautionary leave for at least 14 days and will maintain pay and other benefits during the full length of that leave.”

Some nurses at other hospitals have reported being asked to take their personal paid leave to cover periods of mandatory quarantine. California has one of the strictest nurse-to-patient ratios in the country, with one nurse for every two sick patients in intensive care units. Some nurses said they were concerned that hospitals would struggle to meet that quotient if too many were forced into quarantine.