The descenders in this section all have specialist applications; mostly in either industry or caving. For Figure of 8's, Grigris and other descenders for rock climbing and sports abseiling see Climbing Descenders.
There are two options; the Stop or the Rack both made by Petzl. In general the Stop is more versatile and safer but can give a jerky descent on long pitches or thin ropes. The Rack allows a greater variation of friction, both through the number of bars used and the spacing of the bars. It gives a beautifully smooth descent and is particularly appreciated on pitches of 50m or more, it is however more difficult to protect yourself, especially when rigging.
Industry and Rescue
The ID is a handle pull Roped Access descender whose speed is controlled by gripping the rope. It is suited to steep descents with stops on route and can be used for short sections of ascent when combined with a handled ascender. If the handle isn't pulled the device grips, if the handle is released it locks, if the handle is overgripped in panic it locks and if the rope is put in wrongly it locks, making it as foolproof as it is possible to be. This device was developed by Petzl to replace the older, less fail-safe devices, which are still used for Climbing and Caving (see above).
The diagram to the left shows the ID being used as a descender.
Back Up Devices
While not strictly descenders, these devices are used to back up a descent (or ascent). The Petzl ASAP is designed for use in industrial applications, and is installed on the second line, also know as the safety line. This is shown in the picture on the left. As the worker moves up or down the device moves as well, and it will lock very quickly in a fall. It can also be used on its own as a fall-arrest device on roofs and slopes, as shown to the right, or when climbing scaffolding or masts, by attaching it to a line fixed to the top and bottom of the structure.
The Petzl Shunt has been around much longer, and is the preferred device for cavers and climbers as an abseil back-up device. Note the ASAP is designed to be used with a shock-absorbing lanyard. The lanyard designed for the purpose is the ASAPsorber, which can be found in the Lanyards section.