Natural geologic bodies (rocks and derived soils or sediments), as well as building materials prepared from them can constitute an important source of ionizing radiation, mainly due to the presence of uranium, thorium and potassium radionuclides in minerals. Studies on the possible health effects of such radiation have been mostly dedicated to assessing radiation doses in indoor environments both in terms of Rn concentrations and external gamma radiation (especially in relation to building materials). Radiological hazards assessments considering external gamma radiation need to consider the amount of time of exposition to the radiation source and hence outdoor situations have been less considered. However, there are at least three situations where the potential radiological hazards associated with objects in the outdoor might deserve attention:

- occupancy of structures made of materials with low shielding to gamma radiation;

- spending a high amount of time in the outdoors, especially for workers in activities related to geologic materials extraction such as open mining or quarry (it will be considered that underground mining is a case of indoor environment) and homeless people;

- work areas in terrains with anomalous high contents of radioisotopes, both naturally or as a result of concentration due to human activities (waste deposition) which might also affect other organisms.

In the present work, it is pretended to present an overview of the potential radiological hazards related to external gamma radiation in outdoor situations.