At ~10:12 PM, Westmorland 911 dispatched Station 20 (Murrysville VFC) for an activated carbon monoxide detector in a home on Impala Drive. Station 20 responded with Engine 20 (4 firefighters including Lieutenant 20 and Sergeant 20) and an additional firefighter manning Station 20. Upon Engine 20's arrival at the scene, the home's occupants had evacuated the structure. Engine 20 firefighters entered the home, monitored the interior using four gas meters and found no concentration of carbon monoxide. Upon further investigation, it was found that home's carbon monoxide detector had malfunctioned and needed replacement. Lieutenant 20 recommended to the home owner to replace the defective detector. Lieutenant 20 returned Engine 20 to service.