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Stand-Up Forklift Egress Times as a Function of Operator Compartment Guarding

Richard M. Ziernicki, Ph.D., P.E.
Ben T. Railsback, M.S., P.E.
Steve D. Knapp, P.E., CFEI, CVFI
William H. Pierce, P.E.
Ricky L. Nguyen, M.S.

A significant hazard related to the use of stand-up lift trucks, or stand-up forklifts, is the hazard of a lower limb crush injury or foot crush due to the opening across the rear of the operator compartment. According to one lift truck manufacturer’s statistics, there have been over 500 accidents that resulted in an injury to the lower limb of the operator in the last 30 years that involved their stand-up lift trucks. [1] Other manufacturers have had similar accidents. The injuries have occurred to the lower limb of the operator due to the close proximity of the operator’s lower limbs to the exterior of the lift truck, and the confined areas that stand-up lift trucks operate in. The operator’s lower limb can become pinned and crushed between the moving lift and another fixed object such as a rack system, a column or another lift truck. Objects, such as a fork tine, can also intrude into the operator compartment, injuring the operator’s lower extremities.

The ANSI/ITSDF B56.1, Safety Standard for Low Lift and High Lift Trucks, encourages stand-up lift trucks to be designed with an open compartment to permit easy ingress and egress. [2] According to the standard, the open design allows an operator a free and easy egress from the truck in the event of a tip-over or off-the-dock accident. However, the standard permits the use of additional guarding and enclosure of the operator compartment. Spring loaded doors (or spring assisted closing guards) have been designed, implemented and are available from many manufacturers, but no data has been published regarding the time to open and egress from the operator compartment. Latching doors have also been designed and manufactured, but are not currently available on the market except in the case of trucks equipped with freezer cabs, for operation in refrigerated environments. However, latched doors have been criticized for extending the egress time duration by approximately ½ second.

This study shows that a spring loaded door can be implemented on a stand-up forklift while only increasing egress time by a negligible amount, 0.05 seconds over an open compartment configuration. Furthermore, this study shows that an optimized latching door, designed by Knott Laboratory engineers, can also be implemented for a stand-up forklift while only increasing egress time by 0.09 seconds. The latching door designed by Knott Laboratory decreases the change in egress time associated with a latched door by a factor of 5. Therefore, the addition of a spring loaded door, or a latching door will not significantly increase operator egress time and provide additional protection to the operator in the event of a collision while still maintaining quick egress.

Published By

2014 ASME International Mechanical Engineering Congress and Exposition IMECE2014-38847
November 19, 2014