The stirring and mixing devices commonly found in laboratories include stirring motors, magnetic stirrers, shakers, small pumps for fluids and rotary evaporators for solvent removal. These devices are typically used in laboratory operations that are performed in a hood, and it is important that they be operated in a way that precludes the generation of electrical sparks.
Use only spark-free induction motors in power stirring and mixing devices or any other rotating equipment used for laboratory operations. While the motors in most of the currently marketed stirring and mixing devices meet this criterion, their on-off switches and rheostat-type speed controls can produce an electrical spark because they have exposed electrical conductors. Do not control speed of an induction motor operating under a load should with a variable autotransformer.
Consider the consequences of stirrer failure, electrical overload or blockage of the motion of the stirring impeller. Stirring and mixing devices, especially stirring motors and magnetic stirrers, are often operated for fairly long periods without constant attention.