Crews from the Anaheim and Santa Ana fire departments and members of the Orange County Sheriff's Bomb Squad evacuated about 400 people from the Tenet Health System building after an employee found the powder in an envelope, the Orange County (Calif.) Register reported Thursday.

Maria Barrios, a support services operator for Tenet, said four employees who were near the envelope when it was opened were quarantined while the crews investigated.

Anaheim police Sgt. Rick Martinez said the substance was found to be cake mix. He said the sender of the package was contacted and was apparently baking a cake before mailing the envelope.