Complex sentence: Propane is nontoxic; however, when abused as an inhalant, it poses a severe asphyxiation risk usually through hyperventilation which leads to oxygen deprivation, hypoxia and sudden loss of consciousness.
Split into simpler sentences: Propane is nontoxic; however, when abused as an inhalant, it poses several risks. Additionally there is a risk asphyxiation usually through hyperventilation which leads to oxygen deprivation, hypoxia and sudden loss of consciousness.