A definition of Gehenna from http://www.jewishencyclopedia.com/view.jsp?artid=115&letter=G
Ludwig Blau Nature and Situation.
The place where children were sacrificed to the god Moloch was originally in the "valley of the son of Hinnom," to the south of Jerusalem (Josh. xv. 8, passim; II Kings xxiii. 10; Jer. ii. 23; vii. 31-32; xix. 6, 13-14). For this reason the valley was deemed to be accursed, and "Gehenna" therefore soon became a figurative equivalent for "hell." Hell, like paradise, was created by God (So?ah 22a); according to Gen. R. ix. 9, the words "very good" in Gen. i. 31 refer to hell; hence the latter must have been created on the sixth day. Yet opinions on this point vary. According to some sources, it was created on the second day; according to others, even before the world, only its fire being created on the second day (Gen. R. iv., end; Pes. 54a). The "fiery furnace" that Abraham saw (Gen. xv. 17, Hebr.) was Gehenna (Mek. xx. 18b, 71b; comp. Enoch, xcviii. 3, ciii. 8; Matt. xiii. 42, 50; 'Er. 19a, where the "fiery furnace" is also identified with the gate of Gehenna). Opinions also vary as to the situation, extent, and nature of hell. The statement that Gehenna is situated in the valley of Hinnom near Jerusalem, in the "accursed valley" (Enoch, xxvii. 1 et seq.), means simply that it has a gate there. It was in Zion, and had a gate in Jerusalem (Isa. xxxi. 9). It had three gates, one in the wilderness, one in the sea, and one in Jerusalem ('Er. 19a). The gate lies between two palm-trees in the valley of Hinnom, from which smoke is continually rising (ib.). The mouth is narrow, impeding the smoke, but below Gehenna extends indefinitely (Men. 99b). According to one opinion, it is above the firmament, and according to another, behind the dark mountains (Ta'an. 32b). An Arabian pointed out to a scholar the spot in the wilderness where the earth swallowed the sons of Korah (Num. xvi. 31-32), who descended into Gehenna (Sanh. 110b). It is situated deep down in the earth, and is immeasurably large. "The earth is one-sixtieth of the garden, the garden one-sixtieth of Eden [paradise], Eden one-sixtieth of Gehenna; hence the whole world is like a lid for Gehenna. Some say that Gehenna can not be measured" (Pes. 94a). It is divided into seven compartments (So?ah 10b); a similar view was held by the Babylonians (Jeremias, "Hölle und Paradies bei den Babyloniern," pp. 16 et seq., Leipsic, 1901; Guthe, "Kurzes Bibel-wörterb." p. 272, Tübingen and Leipsic, 1903).
How does the WTS evade the issue of "burning fire" given the original conception of gehenna as a firey wasteland? Another etymological misinterpretation by Fred Franz?