Even working vacuum pumps, when used improperly, can pose a number of safety hazards to users. Learning to use pumps safely is part of the training lab techs undergo.
Poorly functioning vacuum pumps, on the other hand, are almost always unpredictable, untrustworthy, and unsafe. With oil-based vacuum pumps, you can even experience safety issues like off-gassing as a byproduct of contaminated pump oil.
Related: Find out how Central Washington University sets the benchmark with their Standard Operating Procedure for Vacuum Pump Safety.