הלכות טומאת מת

When the contents of any implement that is sealed close are protected from impurity, all of the contents are protected: food, liquids, clothes, and keilim that can be purified in a mikveh.
This is the Scriptural Law. According to Rabbinic Law, however, earthenware containers which are sealed close protect only foods, liquids, and other earthenware containers inside of it. If, however, keilim that can be purified in a mikveh or garments were in an earthenware container that was sealed close, they are impure.
Why did the Sages decree that they do not protect everything like other containers that protect their contents from impurity? Because the other containers that protect their contents do not contract impurity and earthenware containers do contract impurity. An impure container does not intervene in the face of impurity and all of the containers of the common people can be assumed to be ritually impure, as will be explained.
Why did the Sages not decree: an earthenware container of a common person does not protect anything from impurity, but a container belong to a chaver does protect everything because it is pure? Because a common person does not consider himself as impure. He will say: Since an earthenware container that is sealed close protects all its contents, there is no difference between me and a chaver. Therefore the Sages decreed that the seal should not protect everything.
Why did they say that it protects food, liquids, and earthenware containers from impurity? Because [regardless] these three types of entities are impure because they come from a common person – before they were located in an ohel where a corpse is located or after they had been located in such a place – [although they were in a container] that was sealed closed. A chaver will never borrow food, liquids, or earthenware containers from a common person except under the assumption that they are impure, for these entities can never be purified. Thus a stumbling block will never arise.
A chaver will, however, borrow keilim that can be purified in a mikveh from a common person. He will immerse them in a mikveh to purify them from the impurity they contracted from being touched by a common person, leave them until the evening and then use them for pure food. Therefore our Sages were concerned that a chaver will borrow keilim that can be purified in a mikveh from a common person that were sealed close in one of his earthenware containers. Now the common person will think that this container was protected, when in truth it has contracted the impurity that lasts seven days. The chaver will immerse these containers, leave them until the evening and then use them for pure food. Thus a stumbling block will arise. This is the reason it was decreed that sealing an earthenware container close would not protect the keilim that can be purified in a mikveh which were in it.

When a person was placed inside a cask that was sealed close, he is pure. This applies even if the cask was made a covering for a grave. It appears to me that the Sages did not decree that an earthenware container sealed close would not protect a person from impurity, because it is an infrequent situation. And our Sages did not enact decrees concerning infrequent situations.

The word of common people is accepted with regard to a container used for the ashes of the red heifer or sacred foods if they say they are pure. The rationale is that even common people are very careful in this regard. Therefore all entities are protected from impurity when their container is sealed close even though it is of earthenware.

The following laws apply when there is an aperture between a home and a loft and there is an earthenware dish placed over the aperture. If the dish has a hole large enough to allow liquids to seep in, the dish is impure, but the loft is pure.
If the dish is intact, everything in the loft - food, liquids, and earthenware containers - is pure, but a person and keilim that can be purified in a mikveh are impure, for an earthenware container intervenes in the face of impurity only for food, liquids, and earthenware containers. Everything in the loft is pure, as if it is in an earthenware container that is sealed close. A person in the loft was deemed impure, because that is a common situation. Therefore if there was a metal container or the like filled with liquids in this loft, the container contracts the impurity that lasts seven days, but the liquids are pure.
If there was a woman kneading dough in a wooden kneading trough in this loft, the woman and the kneading trough contract the impurity that lasts seven days, but the dough is pure as long as the woman is kneading it. If she ceased and then touched it again, she imparts impurity to it. Similarly, if one moved the dough or the liquids to another one of the keilim that can be purified in a mikveh that were in the loft, they become impure due to contact with the other container.
If the k'li covering the aperture was one that was not susceptible to impurity and which protect their contents when sealed close, as we explained, in which instance, contact with a common person does not render them impure, or the k'li was an earthenware container that was pure and intended to be used for the ashes of the red heifer or for consecrated foods – in which instance everyone's word is accepted with regard to their purity – it protects everything in the loft. If there was a tent erected in the loft and a portion of its fabric was draped over the aperture between the house and the loft, it protects [everything in the loft] even though its roof is not positioned over the loft. [The rationale is that] a tent protects when it covers, as we explained.