The Machine Operator’s Jammed-Feedstock-Clearing Task: A Safety Design Challenge

Workers are often exposed to injury risk from sudden and unexpected machine movement when clearing jammed material from process machinery. An engineered safety response can effectively intervene to control or eliminate this risk. Backstrom and Doos (1998) found that about 25% of injuries involving automated machinery were preceded by a disturbance in process material flow such as a piece of material becoming stuck, crooked or getting in an otherwise faulty position. In the US, lockout is required when an employee is required to place any part of his or her body into an area on a machine or piece of equipment where work is actually performed upon the material being processed (point of operation) or where an associated danger zone exists during a machine operating cycle. Minor tool changes and adjustments, and other minor servicing activities, which take place during normal production operations, are not covered by the OSHA lockout standard if they are routine, repetitive, and integral to the use of the equipment for production, provided that the work is performed using alternative measures which provide effective protection [emphasis added] (OSHA, 1989). Machine control systems that can automatically detect and respond to hazardous operating conditions could be a way to reduce machine-related injury and fatality rates. Accurate laboratory testing criteria, based on key patterns manifested by the machine during hazardous events are vital to developing such new safety technology. This paper discusses safety design challenges in designing reliable safeguarding associated with machinery.