The American Ladder Institute defines a fixed ladder as one that is not self-supporting, non-adjustable and permanently attached to a structure. An example would be a ladder attached to a large water tank that allows access to the tank opening. The Occupational Health and Safety Administration (OSHA), a division of the U.S. Department of Labor, publishes regulations concerning the design, maintenance and use of fixed ladders. Compliance with these regulations prevents accidents.
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Fixed ladders must carry a single concentrated load of at least 90.7kg. If a ladder is intended to carry more than one 90.7kg. load at a time, this must be factored into the design. When designing the rails and fastenings, you must add the weight of the ladder and all attached appurtenances, such as cages and landings, to this minimum weight requirement. The fastenings must withstand the entire intended load if it is concentrated to produce maximum stress on the fastenings.
Rungs and Rails
The rungs on metal ladders must have a minimum diameter of 3/4 inches, and on wood ladders, 1 1/8 inches. The spacing must be uniform and cannot exceed 12 inches. The rungs must be designed so that a foot cannot slide off the end. The side rails must provide an adequate gripping surface without sharp edges, splinters or burrs. If metal is spliced to form the rails, the splice must be a smooth transition with no sharp edges. If dissimilar metals are used in the splice, you must take steps to prevent corrosion from electrolytic action.
You must install a fixed ladder at an angle between 60 and 90 degrees, although the preferable angle is between 75 and 90 degrees. You must provide a minimum clearance of 30 to 36 inches on the climbing side of a ladder and a minimum clearance of 7 inches between the back of the ladder to any permanent surface unless there is an unavoidable object, like a girder, in the way. The clearance on either side must be 15 inches. You must paint metal ladders to prevent corrosion, and treat wood ladders with a preservative if the wood is in conditions where decay could occur.
Cages and Platforms
Ladders between 20 and 30 feet long must have a cage, which must begin 7 to 8 feet from the bottom, extend 42 inches above the top landing and must be 27 inches wide and have vertical bars spaced no less than 40 degrees apart. Ladders longer than 20 feet must also have landing platforms. If there is no cage, the platforms must be spaced 20 feet apart; but when there is a cage, the platforms can be 30 feet apart. Platforms must have a minimum width of 24 inches and a minimum length of 30 inches.
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