B737 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Flight Crew Last 90 Days 159.47; Flight Crew Total 1775.42; Flight Crew Type 1775.42
Communication Breakdown; Situational Awareness
Deviation / Discrepancy - Procedural Hazardous Material Violation; Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action; General Work Refused
Human Factors
While performing the preflight walk around; the First Officer became aware of a spill in the aft cargo compartment and a Ramp Service Agent was complaining of a burning sensation in his lungs when the rear cargo bin was opened upon arrival of the previous flight from ZZZ1. We were originating in ZZZ. I was on the flight deck and when the First Officer informed me of the situation. We had already started boarding. I went up to the Gate Agent and told him to stop boarding. On my way back down the jetway; there was a Ramp Agent and she informed me that everything thing was okay and we could continue boarding. Shortly after making my way back to the flight deck the deice man came into the flight deck and informed me that ramp personnel had told him to stay away from the aircraft due to the spill. I then went outside to the aft cargo bin and there were several ramp service agents and a Dangerous Goods Specialist. The suspect container was outside the aircraft. The Specialist stated that there were no dangerous goods on the manifest for the inbound flight; and they were unsure of what the liquid was. Eventually; the DG Specialist was able to locate info about the spilled cargo. This info stated that it was 'harmless pharma.' The labels on the container itself did not support this. Eventually the DG Specialist stated that it was acetone. (Our FOM uses acetone as an example of DG) I made an ELB entry that there was a Hazmat spill in the aft cargo bin. I called the [Chief Pilot] to get him in the loop on this.  When Maintenance made it to the aircraft; the technician was understandably uncomfortable with cleaning up the spill. When other technicians arrived; they could not determine if there was any accumulation under the magic carpet without taking it apart. Without a thorough inspection of the aft cargo bin; I was not comfortable with the aircraft. Maintenance did not release the aircraft. We got a swap after 3 hours. There was substantial confusion between Ops and Maintenance during the entire process.
B737 Captain reported undocumented Hazmat liquid cargo spill resulting in aircraft swap after a three hour delay due to disagreement between flight crew; Operations; and Maintenance.