1. Field of the Invention
Ladders for use in manholes such as molded plastic (e.g. high density polyethylene) for use in manhole construction.
2. Description of Prior Procedures
The prior ladders are constructed from metal and use "shepherd books" hanging from the bottom step of the bottom riser section (riser section immediately above the manhole base) by hanging the ladder on the rung of the manhole step which places a hazard in the climber's way as well as reducing the space needed by the climber. Metallic ladders which are constructed from galvanized steel, are subject to rust in the manhole sewer environment; whereas the present ladder may be constructed from non-metallic materials, such as being molded from high density polyethylene (HDPE). Also, in the metallic ladder construction the contractors often cut the ladder verticals in order to shorten the ladder if it s too long, which damages a galvanized (i.e. rust resistant) coating thereby increasing the risk of corrosion and/or breaks into the coating or covering of the metal thereby exposing the metal to rapid corrosion. The present non-metallic ladder is not subject to corrosion, especially if cut to shorten the ladder or otherwise. In addition, the present ladder does not interfere with the path of the climber, nor does it interfere with the use of the ladder rung because the present ladder is placed on the leg of the step thereby increasing the load bearing capability of the step and the ladder as well. Where the prior "shepherd hooks" bang from the rung, the present ladder snaps and locks into place at an attachment point which may be shaped and contoured to fit securely on the step legs thereby reducing the possibility of the ladder being dislodged Therefore, almost a full tread width of the step is usable and available without obstacles which would endanger the climber. The present ladder attachment method provides for much higher degree of worker safety and security realizing that there's always danger that a workman will slip and fall to the bottom of the manhole.
Other and further objects and advantages of the present ladder will become apparent upon reading the ensuing specification in conjunction with the drawings.
USPTO Backgrounds
USPTO Backgrounds