Which statement about portable electric lights used in petroleum product tanks is TRUE?

The statement regarding portable electric lights used in petroleum product tanks that is true emphasizes the need for safety in environments where flammable vapors may be present. Portable electric lights must be explosion-proof and typically operate on self-contained, battery-fed power sources to prevent sparking and electrical faults that could ignite the surrounding flammable atmosphere.

Battery-operated lamps reduce the risk associated with electrical connections that might occur with plugged-in appliances. These lamps are designed specifically for hazardous environments and comply with safety regulations that require explosion-proof equipment to minimize the chance of ignition in areas where flammable fuel vapors may exist.

The other options do not adequately address the specific requirements or safety protocols relating to the use of portable electric lights in petroleum tanks. For instance, while grounding is important for electrical safety, the characterization of the lights being solely self-contained and battery-fed is a more definitive requirement than stating they can simply have a ground wire.