A man described as a recently fired employee of the Hillel UW in the University District was arrested Monday afternoon after he threatened to blow up the building, according to Seattle police.

The threat prompted a significant law-enforcement response and closed streets in the area for about two hours.

At 1:45 p.m., employees at the Karen Mayers Gamoran Family Center for Jewish Life building at 4745 17th Ave. N.E., also known as Hillel UW, contacted police and said the former employee had threatened to mix toxic chemicals to cause an explosion, police said.

The man, reportedly a 28-year-old former maintenance worker, then headed for a supply closet, mixed ammonia and bleach together, and inhaled the fumes, according to police.

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The mixture produces chloramines, and exposure to chloramine gas can cause symptoms including coughing; irritation to the throat, nose and eyes; and pneumonia, according to the Washington State Department of Health.

Employees evacuated the building and told police the man might have a knife, according to police. A police SWAT team found the suspect in the basement just before 3 p.m.

The man was affected by the fumes, police spokesman Mark Jamieson said, so officers had to make a plan to guide him out of the basement.

Once he followed their instructions to move toward them, he was taken outside and hosed down.

The man, who reportedly has a history of suicide attempts, was taken to Harborview Medical Center for treatment.

No one else was injured, police said.

The man will undergo a mental-health evaluation, they said.

Hillel UW employee Dylan Siegel, 20, called the center a welcoming place where everyone gets along. He has worked at the center’s cafe for about two years and said he likes going there to hang out with friends.

The organization serves as a community group for Jewish students and aims to “empower Jewish students and young adults to create vibrant communities that cultivate ownership of identity, sense of Jewish relevance and appreciation of the diverse and complex Jewish experience,” according to its website.

Siegel, a UW junior from San Diego, said he felt confused as he watched officers and firefighters go in and out of the building.

“I can’t think of anyone who would have done this,” he said.

Hillel UW closed Monday evening but will be back in operation Tuesday. Employees said they were shaken up but glad everyone was safe and had responded to the emergency the way they had practiced.

Police closed off traffic along 16th Avenue Northeast and 17th Avenue Northeast near Northeast 50th Street during the investigation.

The scene remained closed until around 4:20 p.m. while hazmat officers cleaned up and made sure the building was safe to enter.

Paige Cornwell: pcornwell@seattletimes.com or 206-464-2517.