Electrical units operating in areas exposed to flammable vapors should?

Electrical units operating in areas exposed to flammable vapors should be explosion-proof to ensure safety in hazardous environments. Explosion-proof equipment is designed to contain any internal explosions without allowing flames or hot gases to escape, thus preventing ignition of flammable vapors in the surrounding atmosphere. This design consideration is crucial in wastewater collection facilities and similar settings where flammable vapors may be present, as it significantly reduces the risk of potential explosions and enhances overall workplace safety.

While the other options suggest various safety measures, they do not address the specific requirements for devices working in explosive atmospheres. For instance, merely housing units in a tightly sealed container or utilizing double insulation may not provide adequate protection against the risk of ignition in environments with flammable vapors. Therefore, explosion-proof construction is the most effective and appropriate solution for electrical units in such areas.