Background: This paper presents and discusses the results of the determination of elemental carbon emitted in diesel engine exhaust into the air of workplaces where machines and equipment with diesel engines are used. In order to assess occupational exposure to elemental carbon (EC) as a marker of exhaust gases emitted by diesel engines, 51 ground-based workplaces where people who operate or maintain equipment with this type of engine work were measured. Measurements were also carried out at 9 workplaces in non-coal mines. Material and Methods: For air sampling at workplaces of diesel exhaust emitting machines and equipment located on the surface, a cartridge sampler without an impactor with a quartz filter was used for elemental carbon determination, while for measurements in non-coal mines the Higgins-Dewell Cyclone FH022 respirable fraction sampler was used. The thermo-optical carbon analysis method using a flame ionisation detector was used to determine elemental carbon. Results: Analysis of the results of the determined elemental carbon concentrations at workplaces located on the ground, i.e., in car repair shops, and in the steelworks where combustion forklifts are operated, showed that the highest concentrations of elemental carbon were determined at the old forklift workplaces in the steelworks. The determined EC concentrations at these workstations were 353 μg/m³ and 78 μg/m³, respectively. In the non-coal mines, elemental carbon concentrations were in the range of 7.5–50 μg/m³. Conclusions: Exposure assessment at the surveyed workplace in the steelworks showed the highest 7-fold exceedance of the maximum admissible concentration (MAC) at the position of the combustion forklift operator. At the other surveyed workplaces in the car repair shop the marked concentrations were in the range of 0.1–0.5 MAC or <0.1 MAC. In non-coal mines, the determined concentrations ranged 0.12–1 times the MAC. Med Pr. 2023;74(2):93–102