A "worker" is any response where the members get off the apparatus and do any "work", whether it be firefighting, investigation, or EMS... they're all workers.
To preclude the obvious follow-up question, an "OSW" is an "Occupied Structural Worker", which means the company responded to an incident where there was any smoke or fire in a non-vacant residential building... anything from food on the stove or bad light ballast through 10th alarm qualifies.
The fire companies don't keep stats on responses to or work in vacant or commercial buildings, however the battalion chiefs do, and these numbers are released annually along with the Runs/Workers/OSW's rundown by company
