Ohalos, Chapter 11, Mishnah 9. We are still occupied with a hados, a vault sunk into the floor of a house, and with a kefishah, the large basket used for olives, laid across its mouth. Visualize it: the flooring of the house, whatever material it happens to be made from, brick or cement, contains a hollow chamber. That chamber has side walls of its own and a bottom of its own, and someone has covered its opening with an olive basket. The Mishnah now sorts out the status of keilim lying in several different spots in and around that chamber, first where a meis lies in the house itself, and then where the tumah is found down in the chamber.
Keilim Caught Between the Two Rims
The Mishnah begins with keilim lying "bein sifsei kefishah", between the lips of the basket, and the sifsei hados, the lips of the vault. Pay attention to exactly where such a kli sits: it lies flat on the uppermost lip of the vault's wall, with the basket pressing down on it from above. Such a kli would have to be exceedingly slender, a needle for instance, since it is pinched between the rim below it and the rim of the basket spread over it.
And the Mishnah adds a second position as well: even keilim lying beneath the floor of the hados itself. The cavity has walls on its sides and it has a floor at its bottom, and we are speaking of a kli lying underneath that bottom, buried below it, "ad hatehom", as far down as the depths of the earth reach. In both of these positions the din is tahor.
Why the Tumah Does Not Descend
This calls for an explanation. As a rule, a meis in a house sends its tumah straight downward through the flooring, and no depth of burial helps: a kli concealed under the floor of an ordinary dwelling contracts tumah. Why, then, are these keilim spared? Because the basket spread over the opening of the cavity combines with the cavity's walls into one enclosed unit, which is an ohel in its own right. Here the walls of the hados, along with its bottom situated under the basket, constitute an independent structure, an ohel unto itself, and everything within its jurisdiction is shielded from the start. That accounts for both situations the Mishnah listed: the slender kli pinched between the lip of the vault and the basket lying over it, and the kli buried below the vault's bottom. Every one of them is tahor.
Tumah Down in the Vault Itself
The Mishnah proceeds: "tumah sham, habayis tamei". Where the meis lies down in the vault with the basket spread over its mouth, the house above contracts tumah, and whatever keilim stand in the house receive no protection whatsoever.
Why not? After all, we just said that the basket over the mouth of the pit creates a separate ohel. Should we not say that the tumah is sealed inside that ohel and goes no further? Here we return to the yesod that governs these halachos: tumah must find its way out. And in this case there is no route of escape other than upward, through the house. That is precisely why the basket cannot hold the tumah in and prevent it from spreading into the house.
We are dealing here with the din of tzamid pasil, a sealed kli. A sealed kli saves whatever is inside it from tumah on the outside, but it has no power to hold back tumah that is inside it from getting out.
Keilim Tucked Into the Vault's Walls, With Tumah Above
The Mishnah now turns back to a case of tumah babayis, a meis in the house, only that this time nothing at all covers the mouth of the hados. Keilim are lodged b'chosley hados, within the walls of the cavity, stuck into some hollow or crevice there. The ruling: "im yeish bimkomon tefach al tefach", with a height of rum tefach as well, they are tahor, since a space of those dimensions counts as an ohel by itself. There is a meis in the house, and the complete absence of any covering over the vault changes nothing: a niche measuring a tefach in length, in width and in height is an ohel on its own, and the keilim resting in it are safe.
"V'im lav, tmei'im", and if not, they are tamei. Should the crevice housing those keilim fail to supply a full tefach in each of the three dimensions, the keilim contract tumah, for there is no independent ohel present to guard them.
When the Vault Runs Wider Than the House
The Mishnah finishes with a striking case: "v'im hayu koslei hados" that are "rechavim mishel bayis", where the vault's walls extend past those of the house. This underground chamber reaches beyond the perimeter of the building standing over it. Imagine a dwelling that measures ten feet across while the cavity beneath it measures twelve, so that it protrudes a tefach or more past the house at either end, once toward the yard in front and once toward the yard behind. Somebody standing outdoors in the open air could well be positioned directly above the hados. And understand what the width refers to: not how thick the walls are, but where they stand. The chamber below simply reaches out past the area occupied by the house above.
Here the ruling is "bein kach uvein kach, tehorim": either way, the keilim stay tahor. It makes no difference whether the niche in which they sit has a tefach in every direction or falls short of it; they are tahor regardless. The reasoning is plain: a kli embedded in one of those protruding walls is simply not located within the house. Trace a vertical line upward from its position and you come out in the yard, front or back. The tumah of the house has no access to it.
Reviewing the Mishnah
Let us review. To begin with, a slender kli lying on the upper lip of the vault's wall, squeezed between that lip and the rim of the basket above it, together with a kli buried under the bottom of the hados all the way down, is tahor, because the basket and the walls together constitute an ohel of their own.
Second, should the meis be lying down inside the vault, tumah spreads to the house. This structure is a form of sealed kli, roofed by the basket and enclosed by the walls beneath it, and such a kli protects its contents from tumah on the outside while it is powerless to confine tumah that originates within.
Third, when nothing covers the vault and a meis lies in the house above, keilim wedged into a crevice in the vault's walls stand or fall by the dimensions of that crevice. The space must measure a tefach in each of three directions: length, width and height. Given them, the crevice is an ohel unto itself and the keilim are tahor. Lacking them, it is no ohel, the tumah of the house penetrates the space, and the keilim are tamei.
Lastly, where the chamber beneath the dwelling extends past the outline of the dwelling above, so that a kli set in its wall actually stands outside the house's area, a meis in the house leaves those keilim tahor whether or not the space around them holds a tefach in each direction, since the house's tumah has no hold on ground situated beyond the house.