It should be noted that a manually operated mechanical device could be utilized optimally at a lift rate of 10 to 20 feet per minute under demonstration conditions. Remember that the object of the retrieval process is to extricate the worker within 4 minutes, the rule-of-thumb limit for the onset of brain damage from oxygen deprivation. Therefore, when manually powered hoists are used to provide access from more than a 50-foot depth, a pneumatic operation should be the primary lifting force. Another factor in the 50-foot limit is the static, muscle work duration for upper-body cranking, set at approximately 30 pounds when non-stop for several minutes (5:1 ratio with 12-inch lever arm).
See “Introduction to Fall Protection,4th Edition” page 370.
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