What type of ladder is specifically designed for lowering a rescuer into a trench or manhole?

The gin ladder is specifically designed for lowering a rescuer into a trench or manhole due to its unique construction and operational features. It consists of a frame that allows for stability and can be secured at the top, providing a safe means for personnel to access confined spaces. The design of a gin ladder allows it to be rigged in a manner that keeps the rescuer securely positioned while they are being lowered or raised, which is critical in preventing accidents during these potentially hazardous operations. This specialized function makes it an optimal choice for trench and manhole rescues compared to other types of ladders, which do not cater to the same level of safety and stability required in such situations.