Authorities say powder released when an envelope burst while being handled by state workers posed no threat.

Police in Butte were also looking for a suspect who could be behind the suspicious letter mailed to the Montana Department of Labor from a Butte address.

Three state workers and a Helena city police officer were isolated for several hours Tuesday while emergency response workers performed an initial test on the substance that ruled it out as a threat to safety. The state lab will conduct more tests to verify the finding.

Other workers on the third floor of the Walt Sullivan building were relocated elsewhere for most of the day, and processing of unemployment insurance filings was slowed.

The state says the envelope burst, as if there were a triggering device to distribute the powder.