Ethanol vapor collects in the vac pump oil, lowers it’s viscosity, pump heats up and the ethanol can ignite. A dry ice cold trap will definitely remove most of the risk. As a daily practice for someone who’s inexperienced I definitely wouldn’t recommend it though. A friend at his previous job saw a coworker running a rotary vane on a 20L roto. As he approached the pump to shut it off it blew up and covered him in flaming pump oil. He healed up but I got to throw plenty of Freddy Krueger jokes his way for a while.