Can someone please send me a reference for a Rishon or Acharon that discusses what exactly "Havla" is?
Talmid Rabeinu Peretz (in the Shitah Mekubetzes 22a) says it is something that is caused by the walls of the Bor. It sound like he understands it to be a presence of a trait rather than the absence of air.
This trait might be warmth as we find in Shabbos (48a and elsewhere) - see also Rashi 51a DH Mayim "water adds Hevel (to a Bor)," and Rashi 53a DH d'Ahani "Hevel that enters (its nostrils) at the beginning of its fall can kill it (even if no more Hevel enters at the end of the fall)."
But none of these are definitive proofs and it may still be posited that Hevel is an absence of oxygen.
However, see Zevachim 113b where we find that the Hevel in Eretz Israel at the time of the Great Flood killed its inhabitants (even though there was no water there). The Gemara proves the existence of Havla by the Flood from Rav Chisda's statement that the flood waters were boiling hot. This implies that the "killer-Havla" is heat.
Once again, though, Havla may be a general term for unbreathable air due either to heat or rarification of its oxygen.
Best wishes,
Mordecai Kornfeld
Kollel Iyun Hadaf
Perhaps we are referring to "vapor" (water), sometimes combined with other noxious gasses to form a noxious vapor.
The "killer havla" might have been supercharged/ superheated vapor.
CM
I always thought hevel or havla was fumes found in pits and swamps. Swamp vapors. Methane. Elsewhere we had had havla d'agma and it was also consistent with swamp gases.
Kol tuv,
Sam Kosofsky
Perhaps, but how does water vapor collect in every pit, or noxious vapors?
As for swamp vapors, I think methane is produced by the decomposition of biomass in swamps. That would not apply to a pit or to Israel during the Great Flood.
I just came across a Rashi in Koheles 11:8 who writes that the word Hevel can sometimes refer to "Pur'anus" and "Tzaros" in general (punishment and troubles). Thus Hevel does not refer specifically to "heated" air. On the other hand, it certainly refers to a quality of the air in our Sugya, since we find that it only affects an animal that falls in the pit nose first (Derech Nefilah).
Best wishes,
Mordecai Kornfeld