Safe Distance for Machinery Actuators: Is After-reach Speed a Constant?

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A common setup for industrial machines is to install a pair of actuator buttons a safe distance from the point of operation. Safety codes specify that minimum distance by assuming a constant hand speed of 1.6 m/s. The specific purpose of this paper is to address an important initial question: Is after-reach speed a constant or a variable? If after-reach speed is a constant, then it should be the same: (a) for a waist-level and a face-level placement, and (b) for varying distances within each placement. To examine the adequacy of that value, a simulated power press with a moving ram was set up for measuring actual hand speed for three placements of the buttons. For each placement, a randomized complete block experiment with nine students provided after-reach hand speed data. Results indicated that after-reach hand speed is not a constant because it varies both with placement of the buttons and distance within placement. The authors conclude that setting up a press using mean after-reach speed is a flawed concept. If a normal distribution applies to after-reach speeds of press operators, then half will exceed the mean. It would be more appropriate to use, instead of mean speed, a speed suitable to protect a larger proportion of press operators. The subjects in this study and in prior studies by NIOSH had substantial portions of their after-reach speeds exceed the 1.6 m/s value.


Originally published in Proceedings of the AHFE 2016 International Conference on Safety Management and Human Factors, July 27-31, 2016, (321-331). Springer International Publishing.