The simple answer seems to be from the Gemara Bava Kama bottom 55b, where Rabbi Yehoshua said that one of the 4 things for which one is exempt in a law court in this World, but will be liable for in Shamayim, is where somebody moved his friend's standing corn in the direction of the fire, so that it should catch alight. The Gemara top 56a states that if the fire is able to reach the corn in a Ruach Metzuyah then he is liable in the worldly Beit Din also. It must be that R. Yehoshua is discussing a scenario where the fire will only reach the corn if a Ruach She-Eino Metzuyah blows.

It would seem that, according to this, the same thing would be if one lights in Reshus HaRabim; that one is only liable, in the Halacha of this World, if it can spread in a Ruach Metzuyah.

However, I have seen that some Mefarshim seem to say differently on this, so it requires further study.

Dovid Bloom

The opinion of the Yad Ramah:-

1) Yad Ramah Bava Basra 26a #107 end DH Ishtakach (shortly before DH Naktinan) writes that a Ruach She-Eino Metzuyah is considered as an Ones. If a strong wind suddenly came along this is considered as something unforeseable, and we learn from Devarim 22:26 "You shall do nothing to the girl" and from Bava Kama end 28b that the Torah exempts anything that happened through Ones.

2) Yad Ramah cites the case we mentioned above; where he moved someone's standing corn in the direction of the fire and we say that in Shamayim he will be liable, even for a Ruach She-Eino Metzuyah. He writes that this is because the damager did an action with the item that became damaged; namely he bent it over in the direction of the fire. But if he did not commit any action with the damaged property; he merely lit the fire and it damaged through a Ruach She-Eino Metzuyah, he is totally exempt [even in Dinei Shamayim].

3) Yad Ramah concludes (end #107, end DH Naktinan) that this applies whether he lit the fire in his own domain, or he lit it in Reshus Harabim; he is totally exempt.

4) This exemption only applies if the damage was done through a Ruach She-Eino Metzuyah; since this is an Ones; but if it was done through a Ruach Metzuyah he is liable.

Yasher Koach

Dovid Bloom

According to the Rosh he is liable even if it spreads through Ruach Metzuyah:-

1) The Mishnah top 61b asks that when a person lights a fire in his own property, how far does the fire have to pass through in order that he will be exempt for any damage done? The Rosh makes an inference from the fact that the Mishnah states that he lit up the fire in his own domain. This suggests that if he lit up the fire in his friend's property, however far the fire travelled before doing damage; he will always be liable for the damage done, since he had no permission to light in his friend's property.

2) We can infer from the Rosh that if he lit the fire in Reshus Harabim, he will also always be liable however far the fire travels before it damages, because a person has no permission to light a fire in Reshus Harabim.

3) Chidushei Rabbi Akiva Eiger 61b DH veN'L writes that it seems from the words of the Rosh, that even if the damage was done due to a total Ones, he is still liable for the damage done. For instance, even if there was a fence that should have blocked the fire, but this fence fell down through some circumstance unconnected with the fire, he is still liable. The Rosh makes no conditions, but simply writes that he is always liable.

4) It seems that the Rosh does not agree with the Yad Ramah that I cited in my previous reply. Yad Ramah writes that even if he lit the fire in Reshus HaRabim, he is still exempt if the damage was done because of an Ones. In contrast, the Rosh writes that since the fire was lighted in a non-permitted way, the person who lighted it is liable for all kinds of damage done.

5) Therefore even though a Ruach She-Eino Metzuyah is an Ones, this does not help us according to R. Akiva Eiger. Since he had no right to light the fire in Reshus Harabim, he has to pay for any damage it causes afterwards. According to R. Akiva Eiger, the Rosh maintains that if he lights in Reshus HaRabim he is always liable whether it is a Ruach Metzuyha or Eino Metzuyah.

Dovid Bloom

The Nesivos HaMishpat agrees with his great friend, Rabbi Akiva Eiger:-

1) The Nesivos Hamishpat 155:1 explains the Mishnah 61b. There, Chazal gave the shiur of a distance; between the fire and the damage; that is so large that even if one did not watch over the fire at all, it will not do any damage. Nesivos adds that it follows that, since the shiur is so large, if a Ruach She-Eino Metzuya comes alongs and casues damage, this is an Ones and one is exempt.

2) The Nesivos is dsicussing the Mishnah that states that he lit inside his own domain. The Rosh writes that if he lit in his friend's domain the distances mentioned in the Mishnah do not apply. It follows that what the Nesivos wrote; that if the fire damages due to a Ruach She-Eino Metzuyah this is an Ones and he is exempt; only applies when when he lit in his own property, but if he lit in his friend's property he is liable even though it required a Ruach She-Eino Metzuyah to cause the damage. This is the same as what the Rosh wrote; that if he lit in his friend's property he is liable even if the fire damaged due to a total Ones.

3) So, if we are correct in comparing lighting in his friend's area to lighting in Reshus Harabim; since in both scenarios he lit without permission; it now follows that according to the Nesivos too, if he lit in Reshus Harabim he is liable even if a Ruach She-Eino Metzuyah carried along the fire.

Dovid Bloom

Rav Isser Zalman Meltzer zt'l was in doubt concerning somebody who lit the fire in Reshus HaRabim:-

1) Up to now we have been assuming that lighting a fire in Reshus Harabim is the same as lighting in the property of somebody else, since one is not allowed to do so in either of these places. However I found, bs'd, that Rav Isser Zalman zt'l, in Even Ha-Ezel Hilchot Nizkei Shechainim 2:17 DH Ella, is in doubt on this point

2) The background to this is the sugya in Bava Kama 61b, where a fire was lit and it burnt items that were hidden in the haystack. The Rambam Nizkei Shechainim 14:9 writes that he is only liable if he lit the fire on the property of the owners and it burnt up hidden items on his property, but if A lit a fire in his own property and it spread to the property of B and damaged hidden items. A is exempt.

3) Even Ha-Ezel writes that the Gemara only discusses the difference between lighting in one's own property and in someone else's property but the Gemara never mentions a person who lit the fire in Reshus HaRabim. Even Ha-Ezel writes that one does not have permission to light a fire in Reshus HaRabim, so possibly one is liable for any damage that this caused or, on the other hand, since the Gemara only mentions that one is liable when he lit in his own domain, this might be telling us that if he lights in Reshus Harabim, bedieved is he exempt for damage caused. Even Ha-Ezel does not come to a clear conclusion on this point.

4) Even Ha-Ezel is not discussing quite the same scenario as our's, since he is relating to the sugya of "Tamun"; hidden items in the haystack. However, I think we can say that a comparison can be made. We can say that R. Akiva Eiger writes that if one lights up a fire in someone else's domain one is liable even for a total Ones that happened afterwards. It can be argued that this is because lighting a fire in a stranger's field is worse than lighting it in Reshus HaRabim. Even though one is not allowed to light a fire in Reshus Harabim, it is not as bad as both trespassing and also setting fire. Possibly it is only for the latter combination that we are so stringent and make him pay even for something totally unavoidable that happened afterwards.

Dovid Bloom

It may be that both Yad Ramah and Rosh agree that if he lit in Reshus Harabim he is exempt bedieved:-

1) It may now be possible to suggest a conclusion to this issue. Up to now I was assuming that, according to the Rosh, there is no difference whether he lit the fire in somebody else's reshus or in Reshus Harabim. The reason I assumed this is because Rosh Bava Kama #13 61b writes "since he lit without permission, no distances were specified"; so he is liable however far the fire travelled before damaging. R. Akiva Eiger writes that this means that even though the damage was done later on through a total Ones he still has to pay, since he lit the fire without permission. I assumed that since one does not have permission to light a fire in Reshus Harabim, this means that if one lights in Reshus Harabim, one is liable even if the fire travelled afterwards through an Ones; namely Ruach She-Eino Metzuya.

2) However, now that we saw what Even Ha-Ezel wrote, it may be possible to say differently. Even Ha-Ezel writes that whilst one does not have permission to light a fire in Reshus HaRabim, it still may be that if one did so, bedieved one is exempt because it is not the same as lighting the fire in somebody else's reshus. This gives me the courage to say that the Rosh maintains thst one is only liable if one lights "beShel Chaveiro"; in somebody else's property. The Rosh does not mention Reshus Harabim explicitly, so we can say that he is exempt from a subsequent Ones if he lights in Reshus Harabim.

3) At any rate, we have a doubt concerning what the Rosh holds on this point. In contrast Yad Ramah Bava Basra 26a end #107 writes that "if he did not commit any action at all on his friend's property [i.e. it was not like "kofef kamato" of Bava Kama top 56a -DB] ....since the damage happened through an Ones, whether he lit the fire in his own domain or in Reshus Harabim he is exempt". We learn that Yad Ramah exempts bedieved when he lit in Reshus Harabim. It may be possible from here to resolve the doubt of Even Ha-Ezel. We also notice that Yad Ramah does not mention the person who lit in soembody else's domain, since Yad Ramah may agree to the Rosh that he is liable for this.

4) In short, the suggestion to conclude this topic is that since Yad Ramah writes that he is exempt when he lights in Reshus Harabim, and since there is a doubt concerning what Rosh maintains on this question, we can make peace between the Chachamim and say that the Rosh also agrees that he is exempt.

Dovid Bloom