HazMat crews determined that the substance discovered onboard an aircraft at the Palm Beach International Airport posed no threat to passengers. The aircraft was released no one needed treatement.
The substance, while inert, was sent to an FBI lab for further analysis.
The plane was able to take off from the Palm Beach International Airport around 10:30 p.m. Wednesday night.
Passengers and crew of a Southwest jet were evacuated during the afternoon after the discovery of the powder.
A flight attendant found the substance in a tissue box.
Fire rescue said the plane was Southwest flight 793 to Baltimore. The plane was scheduled to take off at 4:10 p.m.
137 passengers were waiting on the tarmac as the plane was inspected. Chairs were brought out for their comfort.
Kristyn Caddell contributed to this report.