Abstract. BACKGROUND: Heavy mobile equipment operation exposes operators to whole-body vibration (WBV) through the seat. The decision of which seat to retrofit a machine with is usually done statically. OBJECTIVE: To report on the third phase of a three phase project designed to intelligently retrofit seats in heavy mobile machines with the purpose of reducing machine operator WBV exposure. METHODS: Three slag pot haulers were retrofitted with a 6801 Isringhausen seat in which the seat pan cushion was retrofitted with Skydex TM seating material. Vibration dose values (weighted for health), vibration total values (weighted for comfort) and Seat Effective Amplitude Transmissibility were determined from field measurements. RESULTS: WBV was reduced from the first field study to below the upper boundary of the ISO 2631-1 (1997) health guidance caution zone and comfort weighted vibration total values were reduced to the second lowest discomfort rating. CONCLUSIONS: Steel making and other similar industries have been provided with information to more efficiently retrofit existing machines.