A jet pack, or rocket pack is a device worn on the back which uses jets of gas or liquid to propel the wearer through the air. The concept has been present in science fiction for almost a century and became widespread in the 1960s. Real jet packs have been developed using a variety of mechanisms, but their uses are much more limited. A practical use for the jet pack has been in extra-vehicular activities for astronauts because of the apparent weightlessness and lack of friction-creating atmosphere in orbit. The term jet suit is used for a system incorporating a jet pack and associated jets attached to the arms to increase maneuverability. In the most general terms, a jet pack is a wearable device which allows the user to fly by providing thrust. With the exception of use in a microgravity environment, this thrust must be upwards so as to overcome the force of gravity, and must be enough to overcome the weight of the user, the jet pack itself and its fuel. This necessarily requires the jet pack to continually push mass in a downwards direction. While some designs have power and/or mass supplied from an external, ground-based source, flight requires all of a flight's fuel to be carried within the pack. This results in problems relating to the overall mass ratio, which limits the maximum flight time to a few minutes, rather than the sustained flight envisaged in science fiction. Firefighters in some parts of the world use Jet packs which help them to fight fires close to the sea or a water body. The jet packs use water and there is no need for a fire truck or water tank. #jetpack