I don't know anyone who is afraid to walk underneath a cumulus cloud because they are afraid it might fall on them. We don't think of clouds even having weight because they are floating. But, clouds are made up of a physical substance, water, and water is quite heavy, so clouds must have weight. We will explain this "paradox" to you if you read on.
1 cubic kilometer of anything will basically fucking kill you.
What about 1 cubic km of air at one standard atmospheric pressure?
It may take a hundred years, but it will kill you.
Touché