NIOSH equation horizontal distances associated with the Liberty Mutual (Snook) lifting table box widths

A study was conducted to determine the NIOSH equation horizontal distances (dH) associated with the three different box widths (34, 49 and 75 cm) and lift starting heights (floor, knuckle and shoulder) used in the psychophysically based Liberty Mutual lifting tables (Snook 1978, Snook and Ciriello 1991). Data were collected with 12 male and 12 female subjects and three repetitions were performed for each of the nine lifting conditions. No gender effects were observed so male and female data were pooled. The value of dH was positively related to box width but there was also a significant interaction between box width and starting height. When pooled across lift heights the average values of dH were 44, 49 and 57 cm for the 34, 49 and 75 cm box widths, respectively. When pooled across box widths the average values of dH were 52, 45 and 52 cm for the floor, knuckle and shoulder height lifts, respectively. A knowledge of the dH associated with each box width will allow for direct comparisons to be made between the NIOSH and Liberty Mutual outputs. This will facilitate further validation of the NIOSH equations. A variable (GAP) was calculated to indicate the horizontal distance from the ankles to the edge of the box. Previously, this GAP has been assumed to remain constant and values of 15, 20 and 25 cm have been proposed. The GAP was observed to have an overall mean of 23.6 cm with individual condition means ranging from 14.6 cm to 31.2 cm. When pooled across conditions the mean GAP values were equal to dH minus half the box width.