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.
Order your copy of “Introduction to Fall Protection, 4th Edition” today. This invaluable resource will take you from the structure design stage to post construction maintenance. Click to find out more!
