Bava Basra, Chapter 2, Mishnah 8. In this Mishnah we return to the central theme of the chapter: a person who performs an action in his private domain, and even though he does so rightfully, since it causes damage to others - he is not permitted to do it.
The text of the Mishnah:
"Marchikin goren kavua min ha'ir chamishim amah" - One who wants to set up a threshing floor is not permitted to do so close to the city. The meaning of a "goren kavua" (permanent threshing floor) is a threshing floor that produces a large amount of grain, to the point that it is necessary to winnow the grain with a tool such as a pitchfork.
To understand the work of winnowing:
After harvesting the wheat, the grain kernels are still hidden inside the stalks. First, the grain is threshed to separate the kernels from the chaff, but even after threshing, everything is mixed together. How do we actually separate the kernels from the straw? Using the wind: the mixture is thrown into the air, the wind carries away the light chaff, while the heavy kernels fall back to the ground.
When the threshing floor is small, it is enough that the wind naturally scatters the pieces of chaff. But with a large threshing floor, a person is required to winnow by hand with a tool, and then the chaff thrown into the wind scatters far away, enters people's eyes, and causes them pain and damage. Because of this, the owner of the threshing floor must distance himself fifty amos from the city - a distance at which it can be assumed that people's eyes are protected.
"Lo ya'aseh adam goren kavua besoch shelo ela im ken yesh lo chamishim amah lechol ruach":
Even one whose threshing floor stands in his own private courtyard and the courtyard is large, is not permitted to winnow in it unless he has a distance of fifty amos in all directions from his neighbor's property.
"Umarchik minetiosav shel chavero uminiro kedei shelo yazik" - This is not a second, additional reason, but rather an explanation of the reason for the obligation to distance it within his private domain: even in a place where there are no people around, such as an agricultural area, where there is no concern for damage to eyes, the chaff is still liable to damage his neighbor's property:
His plantings: The straw carried by the wind acts like a sponge that absorbs moisture, and is liable to dry out the tender saplings and his neighbor's produce.
His plowed field: The field that has just been plowed is liable to be ruined by the winnowing waste that falls into it, to the point that its owner will need to clean it and tend to it all over again.
In summary: In this Mishnah we learned two laws regarding distancing a threshing floor: distancing a permanent threshing floor fifty amos from the city because of the damage the chaff causes to people's eyes, and distancing it fifty amos in all directions even within his own property - because of the damage that is liable to be caused to his neighbor's plantings and plowed field. And once again the foundational principle of the chapter arises: even one who acts within his own property, as long as his action damages others, he is not permitted to do it.