Complex sentence: With two animals underground (dog and quarry), it is essential that a flow of air be maintained to avoid asphyxiation, and the tigher a dog is in the pipe, the that more air flow will be constricted.
Split into simpler sentences: With two animals underground (dog and quarry), it is essential that a flow of air be maintained to avoid asphyxiation. The tigher a dog is in the pipe, the more that air flow will be constricted.