Cessna 402/402C/B379 Businessliner/Utiliner
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Troubleshooting; Distraction
Deviation / Discrepancy - Procedural Security; Deviation / Discrepancy - Procedural Hazardous Material Violation
General Maintenance Action
Human Factors
Yesterday; [Operations Control] called me to inform me that a white powder had come out of a box at the Post Office and sent a few people to the hospital. I was then called into a meeting with XX; XY; and XZ; regarding the event. The Post Office had been evacuated; so I gave them the numbers of a few of the clerks and was later able to acquire the Post Master's cell phone number. I then went and spoke with XA who also had to fill out a report. The aircraft was put into quarantine as the substance was brought over on either Flight XXXX or XXXY. [In the afternoon]; the aircraft was lifted from quarantine and the Post Office was reopened and I was allowed to finish the day. The substance was found to be horse medicine. The clerks on [Post Office] informed me that it was poisonous to humans and 5 people had been sent and released from the hospital. A safety team was being brought in today to further clear the mail affected by the powder. The box carrying the medicine had been broken and/or was poorly packaged.
Airline Captain reported air cargo container of Class 9 Hazmat leaked white powder due to improper packaging during delivery to recipient.