Trip-nip bars are used to prevent fingers/hands being drawn into in-running nips on machines such as printing presses. However, if trip-nip bars are improperly designed, installed or maintained, they can represent a significant entrapment hazard if the fingers/hand are drawn against them and excessive force is required before the safety mechanism trips, or even after tripping has occurred. Current standards and industry guidance do not advise a suitable method to test whether the crushing pressures on fingers at trip activation are acceptable. This study determined the pressure-pain tolerance limits from a range of subjects. A set of test fingers was designed and calibrated using pressure sensitive film. Field tests of an entrapment hazard using the test fingers were successful and the test method is designed to be repeatable by industry during maintenance checks.
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