A white powder discovered in a package at a business in Upper Hutt on Thursday morning was not toxic.
Forty people were evacuated from a computer data processing company in Lane Street in Wallaceville.
Twenty people were decontaminated as a precaution, while scientists identified the material.
Police say the building, which was cordoned off, is open again and people have been allowed to return.
ESR scientists will conduct further tests to confirm the exact nature of the substance.
