Dr. Carlos Sierra is a Mining and a Geological Engineer with an MSc. in Civil Engineering and an MSc. in Environmental Engineering. Over the past seven years, he has taught mine ventilation courses at the Universities of Oviedo and Cantabria in Spain and at ESPOL in Ecuador. He is currently an Assistant Professor of Mining Methods at the University of León (Spain). He has co-authored more than 30 research articles on environmental engineering and mining engineering.