A simulator of a workstation at a reciprocating motion industrial machine was used to examine selected foot control and task variables for their main and interactive effects upon inadvertent actuations in repetitive, self paced machine operations. The way hand task, working position, pedal difficulty, and pedal feedback affected an increase or a decrease in machine initiation errors at time when such inadvertent initiation could result in equipment damage or operator injury were statistically evaluated. Sixty-four trained factory machine operators between 21 and 59 years of age with work experience on machines using foot controls (6 months to 36 years) were studied. Two dependent variables (simulated injury frequency and equipment damage events) and three covariables (subject age, experience, and the mean number of subjects' hits per minute) were considered. The most striking finding was the way that hit rate (hits/minute) affected the ability of the subjects to control their foot movements and avoid foot switch initiation errors. The threshold or critical speed was approximately 17.5 hits/minute for these tasks. This model suggests two factors which interact to cause inadvertent actuation of foot controls on industrial machines: people make unmediated hand movements in response to the workpiece and machine problems; and out of sequence foot control movements are produced by the effects of normal task rhythm and the loss of operator balance. If production is to continue above the critical hit rate, the authors recommend that causes for inadvertent actuation errors be eliminated by proper die stop design, scrap removal, assignment of foot controlled machine to workers whose hit rate is below the error threshold, and use of hand control instead of foot control. Consideration should be given to using simulation to predict an error threshold, and to having an easier to push foot control for some tasks and a harder to push foot control for other tasks.