Mishnah Oholot 5:1-2 · Expert voice, Standard

Sugya Map

• The Core Issue: Aperture ontology in tumat ohel—specifically, whether a sub-standard vent or utilitarian flue (ein hatannur) serves as a conduit (mavri'ach) to bring corpse impurity (tumat met) into an enclosed space (bayit or aliyah), and whether an earthenware vessel (kli cheres) can suffer localized contamination without projecting impurity beyond its rim.
• Primary Nafka Minot:
  • Dimension of Breach: Whether an opening lacking a handbreadth square (petach tefach) can transmit tumat ohel if it was engineered solely for smoke exhaust (lehotzi ashan) or liquid entry (choneis mashkeh).
  • Asymmetric Portals: Can a conduit permit entry of tum'ah into a vessel's cavity (avir) while simultaneously choking off that tum'ah from breaking out through the vessel’s larger, wide-open mouth into the surrounding room?
  • Barriers of the Demotic: Can an earthenware vessel belonging to an am ha'aretz act as a halakhic screen (chotzetz) over a hatchway (arubah), or does its presumptive subjective defilement corrupt its objective protective capacity?
• Primary Sources: Mishnah Oholot 5:1-2; Mishnah Kelim 8:7; Mishnah Kelim 9:8; Tosefta Oholot 5:1; Talmud Shabbat 95b; Talmud Shabbat 146a; Rambam, Hilkhot Tumat Met 18:4.

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Text Snapshot

Mishnah Oholot 5:1 תַּנּוּר שֶׁהוּא עוֹמֵד בְּתוֹךְ הַבַּיִת, וְעֵינוֹ קְמוּרָה לַחוּץ, וְהֶאֱהִילוּ עָלָיו קוֹבְרֵי הַמֵּת—בֵּית שַׁמַּאי אוֹמְרִים: הַכֹּל טָמֵא. וּבֵית הִלֵּל אוֹמְרִים: הַתַּנּוּר טָמֵא, וְהַבַּיִת טָהוֹר. רַבִּי עֲקִיבָא אוֹמֵר: אַף הַתַּנּוּר טָהוֹר.

Mishnah Oholot 5:2 אֲרֻבָּה שֶׁבֵּין הַבַּיִת וְהָעֲלִיָּה, וּקְדֵרָה נְתוּנָה עָלֶיהָ וּנְקוּבָה בְכוֹנֵס מַשְׁקֶה—בֵּית שַׁמַּאי אוֹמְרִים: הַכֹּל טָמֵא. וּבֵית הִלֵּל אוֹמְרִים: הַקְּדֵרָה טְמֵאָה, וְהָעֲלִיָּה טְהוֹרָה. רַבִּי עֲקִיבָא אוֹמֵר: הַכֹּל טָהוֹר.

Leshon/Dikduk Nuances:

• וְעֵינוֹ (Ve-eino): Not the primary fuel gate, but the auxiliary draft-vent or smoke flue. In Rabbinic Hebrew, ayin denotes a small aperture designed to regulate draft or sight (cf. Mishnah Kelim 8:7).
• קְמוּרָה (K'murah): From the root k-m-r (to arch or vault; Aramaic kivba). The flue extends through the structural wall, vaulted downward or hooded externally to block rain and updrafts, opening laterally rather than skyward (see Tosafot Yom Tov ad loc., citing the Kaf Nachat).
• כּוֹנֵס מַשְׁקֶה (Choneis Mashkeh): The minimal aperture standard for a vessel: smaller than motzi mashkeh (leaking liquid out), admitting liquid inward under capillary action or hydrostatic immersion, yet radically short of a tefach.

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Readings

1. The Geometry of Apertures: Rash mi-Shantz and the Sub-Tefach Threshold

The foundational problem animating the sugya is physical: If the ayin possesses a standard pose'ach tefach (a one-handbreadth square opening), how could Beit Hillel or Rabbi Akiva entertain purifying the house? Once an aperture measures a handbreadth, it is an uncontested halakhic gateway (petach) through which corpse impurity traverses freely. Conversely, if it lacks a handbreadth, by what scriptural mechanics could tum'ah penetrate it at all?

The Rash mi-Shantz (Mishnah Oholot 5:1, s.v. "בש"א הכל טמא") establishes that the Mishnah must be situated in a case where the ayin strictly lacks a handbreadth square:

ובשאין בעין פותח טפח איירי, דאי יש בו פותח טפח למה לא תכנס לבית... ועוד דגבי מגדל אוקמינן בדלתותיו מגופות וכאן פיו של תנור פתוח... אלא בדלית ליה פותח טפח איירי.

Based on this premise, the Rash delineates the tripartite dispute through the mechanics of sub-tefach openings:

                  Corpse Overshadows External Flue (Ein HaTannur < 1 Tefach)
                                             │
         ┌───────────────────────────────────┼───────────────────────────────────┐
         ▼                                   ▼                                   ▼
    Beit Shammai                        Beit Hillel                         Rabbi Akiva
Small hole admits tum'ah             Small hole defiles kli;              Sub-tefach flue is not
into oven; open mouth                does NOT project ohel                a halakhic portal at all.
transmits it to the house.           out of mouth into house.             Both oven & house tahor.
[All Tamei]                          [Oven Tamei, House Tahor]            [All Tahor]

1. Beit Shammai: A hole smaller than a handbreadth serves as an entry portal for an earthenware vessel. Once tum'ah breaches the inner cavity (avir) of the oven, the oven's wide mouth—situated fully within the domestic space—operates as a standard open portal. Because the mouth contains many handbreadths, the impurity bursts forth (boka'at ve-yotzeit) to defile the entire structure.
2. Beit Hillel: An asymmetric barrier. Beit Hillel concedes that a sub-tefach puncture suffices to defile an earthenware vessel internally. However, because the tum'ah gained access via a sub-standard conduit, it lacks the legal virulence (ko'ach ha-ohel) to project beyond the confines of the vessel. The oven absorbs the impurity into its physical walls and airspace, but cannot transmit outward across the threshold of its open mouth to defile the surrounding house.
3. Rabbi Akiva: A sub-tefach orifice engineered exclusively for smoke evacuation (eino asui ela lehotzi ashan) is halakhically non-existent concerning the entry of tum'at ohel. Consequently, the oven remains entirely unblemished.

The Rash reinforces this reading via the Tosefta (Tosefta Oholot 5:1), wherein Rabbi Yochanan ben Nuri and Rabbi Chalafta debate the matter:

"עין של תנור שיש בה גובה טפח ואין בה רוחב טפח, יש בה רוחב טפח ואין בה גובה טפח—טהורה."

Unless a full square handbreadth is present, Rabbi Akiva treats the flue as a sealed solid. The Rash must subsequently harmonize this with Mishnah Kelim 9:8, which stipulates that an oven's flue requires a sealed stopper (tzimid patil) of a spindle's thickness (melo pi chush) to rescue it from corpse impurity. The Rash resolves this by distinguishing between an oven situated entirely within an active ohel ha-met—where, via the legal mechanism of migu (since the main mouth demands a tzimid patil, the auxiliary eye likewise demands one)—and our Mishnah, where the primary mouth rests outside the contaminated sphere in absolute purity.

2. Maharam of Rothenburg: The Doctrine of Teleological Openings (Asui Lehotzi)

The Maharam of Rothenburg (cited in Tosafot Yom Tov ad loc., s.v. "בש"א הכל טמא") rejects the premise that an aperture lacking a handbreadth could ever be subject to dispute regarding ohel. He aligns with the Rosh (Hilkhot Tumat Ohel 18:4), insisting that the ayin measures at least a full handbreadth square.

This shifts the axis of the dispute: If the flue measures a full handbreadth, why does Rabbi Akiva declare the entire ensemble pure, and why does Beit Hillel restrict contamination to the oven?

The Maharam introduces a cross-tractate conceptual identity between Sabbath construction (melechet boneh) and the structural laws of tent contamination (hilkhot ohalot). In Talmud Shabbat 146a, the Gemara establishes:

כל פתח שאינו עשוי להכניס ולהוציא—אינו פתח. (Any opening not constructed both to admit and expel is legally void as a portal).

Biblically (mid'oraita), an aperture must possess a dual, symmetrical utility: ingestion and evacuation. An ein hatannur is constructed solely to expel smoke (lehotzi ashan), never to admit entities. Torah law therefore does not categorize this smoke-duct as a "portal" (petach). By Torah law, the entire ensemble—both oven and house—remains utterly pure.

The Mishnah represents tiers of Rabbinic decree (gezeirah derabbanan):

• Rabbi Akiva: Pure biblical formalist. Since the vent is designed exclusively for egress, the Sages promulgated no decree to treat it as an ingression portal. Alternatively, Rabbi Akiva maintains that where severe financial loss is imminent (hefsed merubah—ruining the entire contents of a house), the Rabbis suspended their decree.
• Beit Hillel: Instituted an intermediate, dialectical decree. The Rabbis penalized the vessel containing the illicit flue, rendering the oven itself impure. However, they refused to extend an artificial, rabbinically fabricated portal to project contamination onto the entire structural house (lo gazru koli hai).
• Beit Shammai: Applied the decree absolutely (ke-ein d'oraita tikun). Once an aperture is treated rabbinically as a gateway to defile the inner vessel, it carries all normal legal properties of a portal, transmitting uninterrupted through the primary mouth into the house.

This reading provides a resolution to Rashi's controversial gloss in Talmud Shabbat 95b (s.v. "עד שיפחת רובו"), demonstrating that an aperture not designed for bidirectional traffic fails the baseline definition of a structural petach.

3. The Rambam: The Physics of Continuous Protrusion and Corpse-Overshadowing

The Rambam (Peirush HaMishnayot, Oholot 5:1; Hilkhot Tumat Met 18:4) departs from both the Rash and the Maharam by reinterpreting the phrase:

וְהֶאֱהִילוּ עָלָיו קוֹבְרֵי הַמֵּת

The pallbearers carrying the deceased did not pass under an aperture, nor did the corpse enter the airspace beneath a flue. Rather, the pallbearers cast an ohel over the arched flue protruding through the exterior wall:

קמורה מקובבת... והוא שיהיה התנור כולו תוך הבית והנקב הקמור בולט חוץ לבית, עוד האהילו נושאי המת במת על זה הקבוב.

[ Exterior of House ]                │ [ Interior of House ]
                                     │
Corpse Overshadows Protrusion        │
             ▼                       │
    [Vaulted Flue / Kibuv] ══════════╪═══════╗
             ▲                       │       ║
      Protrudes Externally           │   [ Oven Body ]
                                     │       ║ (Open Mouth)
                                     │       ▼
                                     │  [ House Airspace ]

The Rambam conceives of the dispute not as a question of sub-tefach aperture transmission, but as an inquiry into the organic integration of a vessel's appendages (chibbur kelim):

• Beit Shammai: The exterior hood (kibuv) is legally unified with the furnace body. When the pallbearers carry the corpse above this vaulted projection, the tent-canopy (ohel) physically and legally locks onto the projection (nidbak ha-ohel bezot ha-kibuv). The tum'ah courses downward through the hollow chimney, fills the core of the oven, and discharges into the domicile.
• Beit Hillel: The exterior hood is a peripheral appendage. Overshadowing it impacts the vessel containing it—defiling the oven because the corpse overshadowed its extremity (she-he'ehil ha-met al miktzato). However, because the corpse did not directly overshadow the architectural boundary of the house, and because the hood's interior is functionally separated from the domestic expanse, the contamination terminates at the oven.
• Rabbi Akiva: The exterior projection is an external fixture (she-ein ha-ohel al etzem hatannur ela al hakibuv ha-yotzei mimenu). Since the core body (etzem) of the oven remained shielded inside the house, and the external hood is not essential to the oven's primary baking utility, the transmission fails. The oven remains pure.

4. The Reversal in Mishnah 2: Earthenware Barriers and the "Am Ha'aretz" Paradox

In Mishnah Oholot 5:2, the tannaitic discourse transitions from an oven flue to a ceiling hatch (arubah) separating an upper story from a lower house containing a corpse, where an earthenware pot (k'deirah) covers the breach.

If the pot is intact (sheleimah), Beit Hillel initially formulated a maximalist doctrine: Kli cheres matzil al ha-kol—an earthenware vessel shields everything within it and beyond it from tumat met. Beit Shammai countered that it rescues only food, drink, and other earthenware vessels (ochel, mashkeh, u-chlei cheres). The Mishnah concludes with a rare halakhic capitulation:

חָזְרוּ בֵית הִלֵּל לְהוֹרוֹת כְּדִבְרֵי בֵית שַׁמַּאי (Beit Hillel retracted their stance and ruled according to Beit Shammai).

The underlying dialetic reveals a fundamental dispute regarding the ontological status of rabbinic impurity in the mechanics of biblical shielding (chatzitzah):

• Beit Shammai’s Challenge: The pot in question belongs to a generic person, presumed to be an am ha'aretz (one unlearned in the meticulous stringencies of ritual purity). An am ha'aretz’s earthenware vessels are deemed impure (tamei le-chaverim) by rabbinic fiat. A well-established canon of taharah states:

  אֵין כְּלִי טָמֵא חוֹצֵץ בִּפְנֵי הַטֻּמְאָה (An impure vessel cannot serve as an interposing screen against impurity).

• Beit Hillel’s Rejoinder: How can Beit Shammai bifurcate the vessel's utility? If the vessel is rendered invalid to serve as a partition because of its am ha'aretz impurity, why does Beit Shammai concede that it shields the food and drink residing in its cavity?
• Beit Shammai’s Triumph:

  "כְּשֶׁטִּהַרְנוּ אֶת הָאֹכָלִים וְאֶת הַמַּשְׁקִין שֶׁבְּתוֹכוֹ—לְעַצְמוֹ טִהַרְנוּ; אֲבָל כְּשֶׁטִּהַרְתָּ אֶת הַכְּלִי—טִהַרְתָּ לְךָ וְלוֹ!"

Beit Shammai exposes an asymmetric subjectivity in rabbinic decrees. The impurity ascribed to the am ha'aretz is non-existent within his own legal frame of reference; he treats his vessels as rigorously pure. When Beit Shammai validates the protection of his food and drink, they operate entirely within the closed subjective ecosystem of the am ha'aretz himself (le-atzmo tiharnu).

However, when Beit Hillel asserts that the vessel acts as an objective barrier (chotzetz) over the ceiling hatch to preserve the chaver's upper story, they convert a subjectively contaminated vessel into an objective universal shield (tiharta lecha ve-lo). Because a chaver recognizes that this vessel is legally defiled by rabbinic decree, that decree strips the vessel of its capacity to act as a mechitzah. Defiled objects cannot block contamination. Beit Hillel was compelled by this internal logic to retract.

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Friction

Kushya 1: The Rash's Contradiction Across Tractate Oholot

In elucidating our Mishnah via the Tosefta, the Rash establishes that if a board (nesar) is placed above an ein hatannur that protrudes outside a house, and corpse impurity is situated outside beneath that board's overhang:

בוקעת הטומאה בין הנסר לתנור ולבית, ונטמא הבית, וטימא הנסר את התנור. (The impurity pierces upward through the junction between the board and the oven, enters the house, and defiles both the oven and the domestic dwelling).

Yet, in Mishnah Oholot 11:4, the Mishnah rules regarding an exterior lintel situated adjacently alongside an open window:

הָיָה מַשְׁקוֹף בְּצַד הַחַלּוֹן וְהֶאֱהִיל עַל קוֹבְרֵי הַמֵּת—בֵּית שַׁמַּאי אוֹמְרִים: אֵינוֹ מֵבִיא אֶת הַטֻּמְאָה! (If there was a projecting lintel beside the window and it overshadowed the pallbearers, Beit Shammai says: It does not introduce the impurity into the house!)

The Rash is arrested by this comparison: Why does Beit Shammai rule in Mishnah Oholot 11:4 that the external lintel does not channel tum'ah through the window, whereas in the Tosefta to our sugya, a board set over the oven flue causes tum'ah to burst upward through the microscopic crevice between board and wall to penetrate the home?

                        The Rash's Contradiction
                                   │
         ┌─────────────────────────┴─────────────────────────┐
         ▼                                                   ▼
Mishnah Oholot 5:1 (Tosefta)                        Mishnah Oholot 11:4
Board over external flue                            Lintel beside open window
Impurity breaches crevice                           Beit Shammai: NO transmission!
House is defiled [Tamei]                            House remains shielded [Tahor]

Terutz: The Architectural Continuity of "Tafus B'Binyan"

The resolution hinges on the structural distinction between a continuous mechanical conduit and independent architectural projections.

1. The Oven Flue (Oholot 5:1): The nesar does not function as an autonomous architectural canopy. It rests physically on the lip of an aperture that breaches the wall envelope. The flue is an artificial tunnel traversing the solid masonry of the house. When a board is placed over this flue, it does not sever the connection; it forms an ohel zafeuf (a congested canopy) continuously grafted to the entry point of the house. The corpse impurity, trapped beneath the board's projection, has no open path upward into the sky. Governed by the canon of tum'ah boka'at (confined impurity pierces and flows toward open paths of least resistance), it courses laterally along the board-flue junction, enters the hollow chimney, and enters the domicile.
2. The Adjacent Lintel (Oholot 11:4): The lintel is a static component of the external masonry situated beside (be-tzad) the window, not over it. When the corpse passes beneath the lintel, the impurity is trapped beneath an isolated exterior roof. The window is a discrete vertical breach with its own distinct boundaries. To cross from beneath the lintel into the window requires the impurity to exit its primary canopy, travel horizontally in open space, and turn at a ninety-degree angle into the window frame. Beit Shammai maintains that ein derech tum'ah le-hikanes—impurity does not execute oblique trajectories around architectural corners unless channeled by a continuous physical envelope.

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Kushya 2: The "Chochah Ve-Itallula" of Beit Hillel's Compromise

In both Mishnah Oholot 5:1 (the oven) and Mishnah Oholot 5:2 (the perforated pot over the hatchway), Beit Hillel adopts a split verdict:

• The vessel itself is rendered impure (ha-tannur tamei / ha-k'deirah t'meiah).
• The domestic expanse beyond it remains pure (ha-bayit tahor / ha-aliyah tehorah).

The Maharam of Rothenburg identifies a logical contradiction within this intermediate ruling. If the aperture—measuring less than a handbreadth—is legally empowered to admit tumat met into the vessel, then the internal airspace of that vessel is an active ohel ha-tamei. The mouth of the oven and the rim of the pot are completely uncovered and measure multiple handbreadths wide.

By what legal mechanic can an open, handbreadth-wide portal spanning an active zone of tum'ah fail to transmit that impurity into the adjacent room? Conversely, if the sub-tefach aperture is inadequate to transmit tent-impurity, why should the vessel itself contract impurity? Is this split not, in the evocative words of the Maharam, chochah ve-itallula (a farcical self-contradiction), arbitrarily bisecting a single transmission chain?

Terutz: The Dual Metamorphosis of "Avir Kli" Versus "Ohel"

The resolution requires separating biblical tumat k'lei cheres (the internal contamination of earthenware) from the laws of ohel (canopy transmission).

Earthenware vessels are subject to a scriptural anomaly derived from Leviticus 11:33:

וְכָל כְּלִי חֶרֶשׂ אֲשֶׁר יִפֹּל מֵהֶם אֶל תּוֹכוֹ—כֹּל אֲשֶׁר בְּתוֹכוֹ יִטְמָא (And any earthen vessel into whose interior any of them falls, all that is inside it shall be unclean).

The Torah dictates that a kli cheres does not contract contamination via its exterior surface (me-achorav), but exclusively through its internal airspace (me-aviro).

                                  Sub-Tefach Breach
                                          │
                   ┌──────────────────────┴──────────────────────┐
                   ▼                                             ▼
       Vessel Internal Mechanics                     Canopy (Ohel) Dynamics
        [Torah / Din Avir Kli]                      [Hilkhot Ohalot Framework]
                   │                                             │
      Capillary/Microscopic Entry                   Requires Full Tefach Gateway
   Suffices to defile cavity space              Deficient opening cannot sustain an
   and render the physical walls tamei.         autonomous, projective Ohel column.
                   │                                             │
                   ▼                                             ▼
            VESSEL IS TAMEI                               ROOM REMAINS TAHOR

1. Contracting Contamination: To render the vessel itself tamei, the tum'ah merely needs to be present within its cavity. Beit Hillel holds that the microscopic breach (choneis mashkeh or a sub-tefach smoke flue) is physically adequate for tum'ah to enter the interior airspace. The physical vessel’s walls absorb the impurity the moment the cavity is penetrated.
2. Transmitting Beyond the Vessel: To convert the entire vessel into a pipeline or conduit that projects impurity outward through its mouth into an upper story or house, a different halakhic mechanism is required: the mechanics of an architectural tent (din ohel). An ohel cannot be mobilized through a deficient opening. Since the aperture entering the vessel lacks a pose'ach tefach, the impurity inside the vessel is halakhically "choked" or static. It defiles the physical container holding it, but cannot establish an active halakhic conduit.

Thus, Beit Hillel’s position is not an arbitrary compromise, but a rigorous separation between the criteria for vessel contamination (tumat keilim) and the criteria for spatial tent transmission (tumat ohalot).

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Intertext

The mechanics of non-functional or sub-standard apertures link our sugya directly to the laws of Shabbat and the general tractate of Kelim.

1. Tractate Shabbat 146a: The Teleology of a Portal

In Talmud Shabbat 146a (Perek Chavit), the Gemara investigates the dismantling of temporary stoppers on the Sabbath:

אמר רב חסדא: פתח שעשאו להכניס ולהוציא—חייב חטאת; להוציא בלבד, להכניס בלבד—פטור... דתנן: עין של תנור קמורה לחוץ... (Rav Chisda said: A breach made to both bring in and take out incurs a sin-offering; to take out alone, or to bring in alone, is exempt... as we learned: An oven whose eye is curved outward...)

The Gemara explicitly applies our sugya in Mishnah Oholot 5:1 to resolve the definition of architectural creation (boneh) on the Sabbath. For a structural puncture to be elevated to a halakhic "portal" (petach), it must possess bidirectional utility. An aperture created exclusively to purge smoke or drain waste lacks the functional ontology of a gateway. This structural principle underlies Rabbi Akiva's stance across both domains: an unidirectional smoke exhaust cannot be treated as an entry gate for tum'ah.

2. Tractate Kelim 8:7 & 9:8: The Variable Metric of the Flue

The definition of an ein hatannur reappears throughout Seder Taharot:

• In Mishnah Kelim 8:7, the Mishnah delineates the exact metric dimensions under which an oven flue ceases to be a liability:

  "עֵין הַתַּנּוּר מִתְּחִלָּתוֹ—אַרְבָּעָה טְפָחִים, וּשְׁיָרָיו—בְּרוֹב."

• In Mishnah Kelim 9:8, regarding an oven exposed within an active tumat ohel, the Mishnah demands:

  "תַּנּוּר שֶׁנִּקַּב מֵעֵינוֹ—שִׁעוּרוֹ מְלֹא פִי כוּשׁ." (If an oven was perforated through its eye, its metric to invalidate a sealed cover is the full thickness of a spindle).

These metrics illustrate the hierarchy of shiurim:

• Melo pi chush (a hairsbreadth/spindle) suffices to disrupt a protective seal (tzimid patil).
• Choneis mashkeh (admitting liquid) serves to admit contamination into a passive pot.
• Pose'ach tefach (a handbreadth square) is required to establish an architectural conduit to defile an entire residence.

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Psak/Practice

In practical codification, the Rambam resolves the disputes of our Mishnayot through his specific architectural paradigm:

1. Halakhic Codification: Mishneh Torah, Hilkhot Tumat Met 18:4

תַּנּוּר שֶׁהוּא עוֹמֵד בְּתוֹךְ הַבַּיִת, וְהָיָה לוֹ נֶקֶב בּוֹלֵט חוּץ לַבַּיִת עָשׂוּי לְהוֹצִיא בּוֹ הֶעָשָׁן... וְהֶאֱהִיל הַמֵּת עַל אוֹתוֹ הַנֶּקֶב הַבּוֹלֵט—הַתַּנּוּר טָמֵא, שֶׁהֲרֵי הֶאֱהִיל עַל מִקְצָתוֹ; וְהַבַּיִת טָהוֹר, שֶׁאֵין הַטֻּמְאָה נִכְנֶסֶת לַבַּיִת דֶּרֶךְ נֶקֶב זֶה. וְאִם יֵשׁ בַּנֶּקֶב הַזֶּה פוֹתֵחַ טֶפַח—אַף הַבַּיִת טָמֵא.

The Rambam rules firmly in accordance with Beit Hillel:

1. If the external flue measures less than a handbreadth square, the oven is defiled (ha-tannur tamei) due to corpse-overshadowing of its projecting extremity, but the house remains pure (ha-bayit tahor).
2. If the flue contains a full square handbreadth (pose'ach tefach), the impurity courses through the flue, fills the oven, and defiles the house (af ha-bayit tamei).

2. Contemporary Applications: Hospital Ventilation and Building Codes

This sugya provides the halakhic foundation for contemporary engineering assessments regarding Kohanim visiting or residing in modern medical centers, funeral homes, and multi-story dwellings:

• HVAC and Exhaust Ducts: Modern air handling units feature fresh-air intakes and exhaust flues penetrating external walls. Under the Rambam’s ruling, an exhaust duct lacking a cross-sectional area of a square handbreadth (approximately 3.15 to 3.54 inches square, depending on the authority) cannot transmit corpse impurity from an exterior loading bay into the internal ductwork of the facility.
• Plumbing Air Vents: Modern building stacks route sewer gas upward through roof vents. Where a roof extends over a loading dock where deceased individuals may be momentarily positioned, these vents do not introduce impurity down into the interior plumbing traps, provided they do not function as bidirectional access portals and their dimensions are structurally compartmentalized.

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Takeaway

Contamination enters vessels through microscopic utility; it captures spaces only through architectural intentionality. A crack defiles the container, but only a doorway can surrender the house.