The blaze broke out at around 11:10 a.m. Saturday, April 1 in Freeport at the EAS Ambulance Company located at 30 Commercial St.
When responders arrived, the building was fully engulfed and had partially collapsed, according to Nassau County Police.
The Freeport Fire Department was joined by 26 other fire departments and 150 fire personnel.
Two Freeport firemen and a Northwell Medical Technician suffered smoke inhalation and were treated at a local nearby hospital.
The fire caused substantial damage.
The investigation is ongoing.
Check back to Daily Voice for updates.
Click here to follow Daily Voice Suffolk and receive free news updates.