When is an electrical device considered explosion proof?

An electrical device is considered explosion proof when it has features designed to contain any explosion that might occur within it and to cool the gases that are produced in such a scenario before they can escape into the surrounding environment. This design is critical in environments, such as mines, where flammable gases or dust may be present. The specific means of achieving this can include robust enclosure materials and devices that allow any pressure build-up to be safely released, thus preventing ignition of external hazardous conditions.

While other options address various characteristics of electrical devices, they don't align with the explosion-proof definition. Operating without a power source or being insulated from electrical currents does not ensure safety in explosive environments. Similarly, being made entirely from non-metallic substances doesn't necessarily guarantee containment of an explosion, as materials must also withstand the pressure and temperature resultant from an internal explosion in addition to potential chemical reactivity.