The students in the dormitory started complaining of headaches and nausea. When the number of students with the same symptoms kept rising, the administration knew something was wrong. The maintenance department dispatched a service technician to investigate. Before the technician arrived, the fire department arrived on the scene. They discovered elevated levels of carbon monoxide in the building. Higher CO levels were recorded in the mechanical room. The students were evacuated and many were sent to the hospital for evaluation. Luckily, there were no deaths. I was curious how something like this could happen.

The underground equipment room had two boilers, an air handling unit and a water heater. One wall featured an exhaust fan vented to the outside. The other wall had a makeup air unit sized to deliver combustion air for the burners and to replace the air removed by the exhaust fan. Typically, these should be electrically tied together, so both must operate simultaneously. In this case, they were not.