Technically & hypothetically, yes. There is no reason why you can not have substantial airflow through this conduct. especially through a hill you easily can have wind or heat differences that creates a pressure difference leading to airflow.
From a risk analysis point of view: No it will not always be safe. See many of the other answers.
In reality you use blowers to make sure that the air insides such a tube is indeed ambient air.
Swissaliciouse t1_j87vncy wrote
Reply to Will a 400m long tube have breathable oxygen inside? by SnekkyGlekky
Technically & hypothetically, yes. There is no reason why you can not have substantial airflow through this conduct. especially through a hill you easily can have wind or heat differences that creates a pressure difference leading to airflow.
From a risk analysis point of view: No it will not always be safe. See many of the other answers.
In reality you use blowers to make sure that the air insides such a tube is indeed ambient air.