Commento su Bava Qamma 6:6

A spark that emerges from under the hammer and damages, is liable, etc...

גץ – a spark of fire.

If a spark flew out from under the hammer and caused damage, he is liable.
If a camel laden with flax passed by in the public domain and its load of flax entered into a shop and caught fire, the owner of the camel is liable. But if the shopkeeper left his light outside, the shopkeeper is liable. Rabbi Judah says: “If it was a Hannukah light, he is he is not liable.”
The first section of mishnah six states that if a person, for instance a blacksmith, were to strike metal with a hammer and a spark were to fly out and burn another person’s property he would be liable.
The second section deals with a scenario that is more likely than it may at first sound. In the ancient world roads inside cities served as shopping areas, just as does the modern day “shuk” in middle eastern countries, including Israel. The roads were generally quite narrow and the fronts of the stores were open to the roads. A heavily laden camel walking down the road could easily fill the entire road. According to our mishnah if the camel’s load of flax were to enter into a shop, catch fire and spread the fire to another person’s property the camel owner would be liable. He should not have allowed his property to trespass into the other person’s shop. If, however, the camel owner placed the fire on the outside, he would be liable. The outside of the store is already semi-public property and he should not have put his candle out there. The one exception to this rule is the Hannukah candle, which is supposed to be placed outside of the home. According to Rabbi Judah, if the candle that caused the fire was in celebration of Hannukah, the storekeeper is exempt.

And the halakah is not like Rebbe Yehudah

רבי יהודה אומר בנר חנוכה פטור – since he is engage in the performance of a Mitzvah. But the Halakha is not according to Rabbi Yehuda.