The current study compared the estimation of momentary time-sampling (MTS) to actual safety performance of three ergonomic responses: back, shoulder, and feet. Actual safety performance was established for the five participants by measuring the target responses with a continuous procedure. MTS 90, 105, 120, 135, 150, 165, 180, 195, 210, 240, and 300 s interval lengths were used to estimate safety performance. Two analyses were conducted. The first analysis found that MTS both under- and overestimates safety performance for all responses when compared with actual safety performance. The second analysis showed the MTS mean error of estimation when compared to actual safety performance across low, medium, and high levels of safety. The overall results suggest the use of MTS with longer intervals shows considerable accuracy (minimal error of estimation). (Contains 4 figures.)