Here are some pictures of a furnace we checked during a recent home inspection. We used an infrared camera to scan the furnace cabinet and found hotspots on the cabinet in excess of 220 degrees F. This is a good indication that the heat exchanger has failed. This can be a fire hazard but also a safety hazard due to combustion gases entering the air supply ducts. We were able to alert the buyer of the hazard and let them know of a costly defect.
Here is a link to a great article covering the dangers of Carbon Monoxide
Thornton Safety and Inspection, LLC
Home Inspectors Brandon MS