A method of performing a selected task in a tank at least partially filled with an energetic substance (12, 14), the method characterized by: - sizing a mobile platform to be smaller than a parallelogram-shaped opening having a width no greater than 36 inches (914.4 mm) and a length no greater than 72 inches (1,828.8 mm); - configuring the mobile platform to include at least: - at least one control unit, - at least one marker detector, - at least one propulsion system, - at least one power supply, and - at least one inherently safe enclosure; - configuring the mobile platform to be inherently safe, wherein the at least one inherently safe enclosure of the mobile platform prevents a spark occurring inside the at least one inherently safe enclosure from passing to an exterior of the at least one inherently safe enclosure, wherein the spark is capable of igniting the energetic substance (12, 14), and wherein all spark-generating components of the mobile platform are positioned inside the at least one inherently safe enclosure; - lowering the mobile platform into the tank using a deployment carrier (50, 764, 780); - at least partially submerging the mobile platform in the energetic substance (12, 14); - detecting at least one marker (320; 902 a,b,c,d; 910) associated with the tank using the at least one marker detector; - generating at least one control signal (308, 310, 312) based on the at least one detected marker (320; 902 a,b,c,d; 910) by using the at least one control unit; - moving the mobile platform using a propulsion system to perform the selected task, wherein the propulsion system is controlled by at least one control signal and uses a rotary power device positioned inside the at least one inherently safe enclosure, and wherein the rotary power device supplies power to a drive assembly positioned outside the at least one inherently safe enclosure; and - using a retrieval carrier (50, 706, 740, 764, 780) to retrieve the mobile platform from inside the tank to outside the tank, wherein no active physical carrier connects the mobile platform to an object exterior of the tank while the mobile platform is in the tank. - sizing a mobile platform to be smaller than a parallelogram-shaped opening having a width no greater than 36 inches (914.4 mm) and a length no greater than 72 inches (1,828.8 mm); - configuring the mobile platform to include at least: - at least one control unit, - at least one marker detector, - at least one propulsion system, - at least one power supply, and - at least one inherently safe enclosure; - at least one control unit, - at least one marker detector, - at least one propulsion system, - at least one power supply, and - at least one inherently safe enclosure; - configuring the mobile platform to be inherently safe, wherein the at least one inherently safe enclosure of the mobile platform prevents a spark occurring inside the at least one inherently safe enclosure from passing to an exterior of the at least one inherently safe enclosure, wherein the spark is capable of igniting the energetic substance (12, 14), and wherein all spark-generating components of the mobile platform are positioned inside the at least one inherently safe enclosure; - lowering the mobile platform into the tank using a deployment carrier (50, 764, 780); - at least partially submerging the mobile platform in the energetic substance (12, 14); - detecting at least one marker (320; 902 a,b,c,d; 910) associated with the tank using the at least one marker detector; - generating at least one control signal (308, 310, 312) based on the at least one detected marker (320; 902 a,b,c,d; 910) by using the at least one control unit; - moving the mobile platform using a propulsion system to perform the selected task, wherein the propulsion system is controlled by at least one control signal and uses a rotary power device positioned inside the at least one inherently safe enclosure, and wherein the rotary power device supplies power to a drive assembly positioned outside the at least one inherently safe enclosure; and - using a retrieval carrier (50, 706, 740, 764, 780) to retrieve the mobile platform from inside the tank to outside the tank,