Which device is specifically designed for use in rappels under 100 pounds?

The figure 8 descender is specifically designed for rappelling and is widely used by climbers and rescuers for controlled descents. Its design allows for smooth, controlled lowering of weight, making it suitable for rappels under various weight limits, including those under 100 pounds. The figure 8 descender utilizes its shape to create friction against the rope, which is essential for managing descent speed and providing safety during rappelling activities.

While a locking carabiner is an important safety component in climbing and rescue setups, it is not designed for direct use in rappelling itself. Similarly, a rappel rack is another descent control device suitable for heavier weights and is typically used for longer descents or with heavier loads. Lastly, a sliding knot, while useful in certain rope applications, does not provide the necessary friction or control required for rappelling, making it an inappropriate choice for this specific scenario.

Therefore, the figure 8 descender stands out as the specialized device tailored for rappelling activities under the specified weight limit.