Turbine room workers had lower exposure to mineral oil than previously described for workers in the mud‐handling areas.12 On the basis of exposure data and job histories, individual exposure to oil mist and oil vapour might be quantitatively estimated in the planned cohort study. In another study, personal exposure to total hydrocarbon compounds has been reported to be up to 450 mg/m3 during work at the shale shakers when drilling with oil‐based mud.10 At an installation with a higher level of enclosure of the mud systems, James et al11 reported the results from two personal samples of workers comprising the mud category operating in the shale shaker room to be 0.06 and 0.40 mg/m3 for oil mist and 3.2 and 35.0 mg/m3 for oil vapour, which were in accordance with the findings presented in Steinsvåg et al.12