45 Minute Daf Yomi Shiur
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In the shiur someone asked about reuven who lights a fire that could travel up until a fire wall, Shimon removes the fire wall after the fire is already burning and the fire continues past where the wall was to damage Levi's property. We said that Reuven is chayav based on אשו משום חציו which is אדם המזיק up until the wall, and chayav based on אשו משום ממונו for anything beyond the wall, just as if the wall would have fallen by itself. Shimon however is a גרמא בניזקין and therefore patur. Although I wasn't sure at the time, it is clear from the gemara BK 27b that Shimon is exempt from damages based on the case where Reuven throws a kli from the roof on to pillows underneath, Shimon then removes the pillows, both are patur.