According to ICAO – Annex 14 Medium Intensity Obstruction Lights – Type A Ex, B Ex or C Ex – have to be used where the obstacle is particularly large and the height of the surrounding ground is more than 45m in hazardous areas. Medium Intensity Obstacle Lights Type A Ex and C Ex have to be used alone, whereas Medium Intensity Obstacle Lights, Type B Ex, should be used either alone or in combination with Low Intensity Obstacle Lights, Type B Ex.