Rescue Squad 3 (commonly called Squad 3) is the heavy rescue apparatus assigned to Firehouse 51. Equipped with specialized tools for heavy rescue, it responds to all working fires and calls requiring technical rescue. Squad 3 is staffed by 4-5 firefighters.
Rescue Squad 3 was originally a 1989 Spartan Gladiator / Saulsbury heavy rescue truck bearing the traditional black-over-red paint scheme of the Chicago Fire Department. Prior to being used on the show, it was in service until 2003 as Unit 5-1-1 of the real life Hazardous Incident Team (HIT), which is the Chicago Fire Department's hazardous materials response team. Later on during Seasons 1 and 2, they occasionally switched between the original squad truck and a 1996 HME heavy rescue also owned by the CFD. Finally during mid-Season 2, the show received a 1989 Spartan Gladiator / 3D-Metals heavy rescue truck from the Antioch (IL) Fire Department and had it repainted for the show. The Antioch rig has been used ever since.
- Officer - Lieutenant Kelly Severide
- Engineer - Tony Ferraris
- Firefighter - Harold Capp
- Firefighter - Joe Cruz
- Jose Vargas - Medically discharged after inhaling toxic fumes.
- Eric Whaley - Floater; temporarily provided relief cover for Kelly Severide
- Kevin Hadley - Dishonorably discharged for misconduct
- Jeff Clarke - Promoted to Lieutenant; transferred to Firehouse 25.
- Peter Mills - Resigned from the department
- Rick Newhouse - Transferred
- Tommy Welch - Floater; temporary relief
- Scott Rice - Discharged after avoiding fires
- Dallas Patterson - Temporarily replaced Kelly Severide as officer due to his rank of Captain; was later promoted to Battalion Chief and then transferred to Firehouse 90.
- Jason Kannel - Still Squad 3, but on a different shift.