Electronic equipment must not be used in the presence of hazardous gas unless it is classified as _________.

The correct answer highlights the importance of safety in environments where hazardous gases are present. Electronic equipment that is classified as intrinsically safe or explosion proof is specifically designed to operate safely in potentially explosive atmospheres. This means that the equipment cannot generate sufficient energy to ignite the hazardous gases surrounding it, thus minimizing the risk of an explosion.

Intrinsic safety is a protection technique for safe operation of electrical equipment in explosive atmospheres by limiting the energy available for ignition. On the other hand, equipment marked as explosion-proof can contain any ignition that might occur within its enclosure, preventing hazardous gases from igniting outside.

Using non-classified electronic equipment in hazardous environments can lead to severe safety risks, including potential explosions, injuries, and fatalities. Therefore, only equipment designed and certified for these conditions should be utilized to ensure the highest safety standards.