Bava Basra, Chapter 2, Mishnah 2. We continue to deal with distancing damages - a person's obligation to distance dangerous things from his property that could damage his neighbor. In this Mishnah, we begin dealing with matters of fire. We must remember that ovens in those days were wood-burning ovens with an open fire.
The required distances for an oven and a stove:
"Lo ya'amid adam tanur besoch habayis ela im kein yeish al gabav govah arba amos" - A person may not set up a baking oven inside the house unless there is an empty space of four amos (about six or seven feet) above it up to the ceiling, so that the ceiling will not catch fire.
"Hayah ma'amido ba'aliyah - ad sheyehei sachtav ma'azivah sheloshah tefachim" - When the oven is set up on the second floor, there is a requirement, in addition to the four amos above it, for a ma'azivah of three tefachim (about eleven inches or thirty centimeters) of plaster in the floor below it, because the support beams on that floor are made of wood and could catch fire from the heat of the oven.
"Uvekirah - tefach" - With a stove, whose heat is less than that of an oven, one tefach (about four inches) of plaster underneath it is sufficient to protect the wood.
These measurements apply even if a person lives on the floor above him, because if the house catches fire, the neighboring houses will also be in danger. Therefore, if a person sets up an oven unlawfully, the neighbors are allowed to protest, take him to Beis Din, and force him to remove the oven from his house.
"Ve'im hizik - meshalem mah shehizik" - and if it caused damage, he pays for what he damaged:
These are the rules for building up to code; however, even someone who followed the rules and yet a fire broke out in his house and damaged someone else's house is obligated to pay. Even though he built lawfully, he must bear responsibility for the damage he caused.
Rabbi Shimon argues and says, "Lo amru kol hashi'urin ha'elu ela she'im hizik patur mileshalem" - they only stated all these measurements so that if it caused damage, he is exempt from paying. In his opinion, the purpose of the measurements - how much airspace and how much plaster to leave - is to define the extent of a person's responsibility. Since he followed the rules and yet a fire broke out, this is considered an oness (circumstances beyond his control), as he acted responsibly, and therefore he is exempt from paying.
The halachah follows the Tanna Kamma: One who acts according to the rules and yet causes damage is liable.
What is the difference between a fire in the house and a fire in the field?
We already learned in Bava Kamma that one who lights a fire outside his house - such as burning garbage - must distance it by certain measurements, and if he maintained the required distance, according to almost all opinions, the halachah is that he is exempt, because it was an oness. If so, why is he liable here even though he followed the rules, whereas there he is exempt?
One answer: Here we are dealing with an ongoing situation - a fire burning in a person's house every day, whose chances of causing an accident are much greater, and therefore extra caution is required. In contrast, lighting a fire in a field is an occasional and one-time event, only for a specific need, and therefore the requirements for it are much lower.
In summary: In this Mishnah, we learned the required distances from the danger of fire - an empty space of four amos above an oven, a ma'azivah of three tefachim below it on a second floor, and one tefach for a stove - as well as the dispute between the Tanna Kamma and Rabbi Shimon on the question of whether meeting the requirements exempts one from damage payments. The halachah follows the Tanna Kamma, and we noted the distinction between a constant fire in the house and an occasional fire in the field.