B737-700
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human-Machine Interface; Time Pressure; Other / Unknown
Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Hazardous Material Violation; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Overcame Equipment Problem; General Maintenance Action
Human Factors
Close to push time; we received our takeoff data when Ops Agent (name) brought Air Waybill XXX-XXXXXXXX for me to sign. I verified the Origin; Flight Number/Date; and Destination. I commented there was no specifications for HAZMAT (Hazardous Materials). I signed the form and we left. While en route; I noticed the note in the Pilot In Command box: 'PIC Verify Dispatch Release remarks indicate HAZMAT. If no HAZMAT remarks is shown; contact the flight's Dispatcher for Dispatch Release revision or amendment.' There were no remarks on the Dispatch Release indicating HAZMAT. There was no wording on the Air Waybill indicating HAZMAT. I contacted Dispatch in ZZZ1 and they had not been notified of any HAZMAT material. He explained the Ops Agent is responsible for advising Dispatch of HAZMAT so the information would be entered in the Remarks section. Initially they were not sure how fire extinguisher and oxygen cylinder were classified but later learned they are considered HAZMAT.
B737-700 Captain reported undocumented Hazmat cargo transported due to erroneous Hazmat documents were provided to flight crew at departure.