We arrive at the sixth and final Mishnah in the sixth chapter of Tractate Bava Kamma. The Mishnah opens with the law of "getz sheyatza" - a spark that flew out from under a heavy hammer striking an anvil. If the spark caused damage, the blacksmith striking with the hammer is liable. However, we must clarify: under which category of liability is he obligated?
Two approaches to understanding the liability:
The approach of Tosafos: Our Mishnah continues the topic of fire that we have been discussing, and therefore the liability falls under the primary category of fire. The underlying assumption is that another force joins the action and causes the damage - the wind that carries the spark or fans it where it lands. The blacksmith's liability therefore stems from the combination of his action and responsibility with another force, and because of this, the exemptions for fire apply, such as the exemption for hidden items - concealed things that one could not expect to be found at the site of the fire.
The approach of the Rema: This is a case of a person causing damage directly. It is direct damage, governed by the same laws as a person shooting arrows. A person is not permitted to shoot sparks into the public domain and ignore where they land, just as he is not permitted to hit balls or shoot arrows into the street. Once he shot sparks and something burned, he bears full responsibility under the category of a person causing damage - and therefore he is liable even for hidden items.
The camel laden with flax:
From here, the Mishnah moves to a new case: a camel that was laden with flax - a highly flammable material - and was passing through the market streets (similar to the narrow market in the Old City of Jerusalem). When the camel is overloaded, the stalks of flax protrude into the shops bordering the public domain. The shops are dark, and their light comes from burning oil lamps; flammable flax entering a place with a lit lamp is a recipe for disaster. And so it happened: the flax on the camel's back caught fire, the camel continued walking, and everywhere it passed, it set things alight and burned them.
The Mishnah states: "Ba'al hagamal chayav" - the owner of the camel is liable. The camel owner acted irresponsibly by overloading his camel, since it is foreseeable that an overloaded camel passing through the market will cause a fire. But for what exactly is he liable?
The law here serves as a kind of review and re-examination of the law of the dog and the baked cake that we learned in chapter 2, Mishnah 3. The camel is walking down the street with fire on its back, and therefore we must distinguish between two types of damage:
What was burned directly: This is considered an extension of the animal's body, just as if the saddle on its back were tearing things off the walls. The category of damage here is trampling, and the liability is for full damage.
What was burned as the fire spread: Here, the law of pebbles applies. As we recall, a law given to Moses at Sinai dictates that damage caused by a force joining the animal's action but not resulting from its direct action - such as a stone kicked from under its foot to a distance - carries a liability for half damages. Fire that flies off and spreads via the wind carrying it is also included in this, and its liability is for half damages.
"Hiniach chenvani nero mibachutz" - if a shopkeeper placed his lamp outside:
The Mishnah continues: if the negligent party is the shopkeeper, who placed his lamp outside his shop - in the public domain, in a place where he should have expected camels laden with flax to pass by - "hachenvani chayav" - the shopkeeper is liable. The camel catches fire and spreads the blaze, and the shopkeeper is liable under the regular and familiar law of fire: he did not guard his fire properly, placing it in a spot from which it could be expected to spread, and it indeed spread due to passing camels. This is like a common wind that he should have anticipated, and therefore he is liable for full damages, according to the law of fire.
And if both of them were negligent - the camel was overloaded and the lamp was placed in the public domain, or the camel owner could have prevented the damage but failed to do so - the responsibility is divided between them: the shopkeeper and the camel owner each pay half of the damages caused by the fire that spread in the area.
Rabbi Yehudah and the Sages regarding the Chanukah menorah:
"Rabbi Yehudah omer: b'ner Chanukah patur" - if the lamp that the storekeeper placed outside is a Chanukah lamp, he is exempt. The Sages established that one must light within the handbreadth adjacent to the entrance, right outside the door, and the optimal way to perform the mitzvah is to place it low and close to the ground, between three and ten handbreadths above the ground. Thus, he did this with the permission and authority of the Sages, and therefore he is exempt.
It is worth noting: Rabbi Yehudah exempts him even though there was a measure of negligence here in leaving a fire in the public domain, and all this is solely because of the optimal way to perform the mitzvah - as he could have raised the lamp to any height up to twenty cubits and fulfilled the obligation of the Chanukah lamp after the fact. Nevertheless, since the Sages instructed to do so ideally and he did so, that is enough to exempt him.
But the Sages disagree: the instruction of the Sages to place a Chanukah lamp outside does not include permission to be negligent and leave it in a place that will cause a fire. Therefore, a person is liable for leaving a lamp in the public domain even on Chanukah, and even though it is a mitzvah - and the halachah follows the Sages.
In summary: In this Mishnah, which concludes the sixth chapter, we learned the law of a spark that flies out from under a hammer and the two ways to incur liability for it - under the category of fire (Tosafot) or under the category of a person who causes damage (the Rema), and the practical difference between them regarding hidden objects. We also learned the law of a camel laden with flax: full damages under the category of Regel for the direct fire, and half damages under the category of Tzroros for the spread of the fire; the liability of the storekeeper under the category of fire when he placed his lamp outside; and the division of responsibility between the two when both were negligent. Finally, we discussed the dispute between Rabbi Yehudah and the Sages regarding a Chanukah lamp, and that the halachah follows the Sages - that even a mitzvah does not exempt a person from his responsibility to safeguard his fire.