Complex sentence: Advantages of the mercury switch over other types are that the contacts are enclosed, so oxidation of the contact points is unlikely; in hazardous locations, interrupting the circuit will not emit a spark that can ignite flammable gasses.
Split into simpler sentences: Advantages of the mercury switch over other types are that the contacts are enclosed, so oxidation of the contact points is unlikely. In hazardous locations, interrupting the circuit will not emit a spark that can ignite flammable gasses.