Cold-storage systems are essential components of cold supply chains. Although order picking technologies have advanced, many of these systems still rely on human labour, where workers are exposed to temperatures below -20 degrees C. Despite wearing protective clothing, prolonged exposure to such cold conditions can lead to cold stress, causing physiological impairments and fatigue, which ultimately reduce performance. Warm rest breaks are crucial to mitigate these adverse effects and maintain productivity. However, there is a dearth of field evidence on the effect of the timing and duration of these breaks on order picking performance. To address this gap, we collaborated with a grocery retailer to examine the impact of rest-break durations on the performance of order pickers in a cold-storage environment set at -21 degrees C. We analysed 514,953 visits to storage locations by 40 order pickers over four months, using a multilevel model with random intercepts and slopes. Our findings revealed a horizontal S-shaped relationship between work time after a break and order picking time, characterised by an initial increase, a stabilisation period, and then a sharp increase. The results suggest that there is an optimal working period following a rest break during which performance peaks before it begins to decline. This period varies depending on the length of the break, highlighting the importance of strategic scheduling to maximise order picking efficiency in cold-storage environments.
