Complex sentence: The majority of those who died were in their 30s and most deaths were attributed to suffocation as well as asphyxiation from toxic fumes emitted from the burning debris rather than the actual heat from the flames.
Split into simpler sentences: The majority of those who died were in their 30s. Most deaths were attributed to suffocation and asphyxiation from toxic fumes emitted from the burning debris, rather than the actual heat from the flames.