(CNN) -- Three people reported falling ill Tuesday after exposure to a suspicious powder in the mail room of the state attorney's office in West Palm Beach, Florida, a city spokesman said.
Initial reports indicate the powder was not hazardous, but the investigation will continue, said Margaret Williams of the U.S. Postal Inspection Service.
Two of the three workers who were sent to a hospital after the exposure complained of headache, nausea and vomiting, Scott said. The third worker complained only of a headache.
A firefighter who responded to the incident was also hospitalized with cardiac problems, city spokesman Chase Scott said. The firefighter was equipped with an air tank, he said, and it was unclear whether his symptoms were related to exposure.
Other employees were in the mail room the envelope containing the powder was opened, but they did not complain of any medical problems, Scott said.
A portion of the building evacuated during the scare was reopened after workers sealed off an air duct connecting it to the mail room.
Scott said the powder was contained in an envelope, but he said authorities were not releasing information about the intended recipient or where it came from.
The FBI, U.S. postal investigators and the Palm Beach Sheriff's Office are jointly investigating the case, Miami FBI spokesman Jim Marshall said.
CNN's Sara Pratley contributed to this report.