Observations of resolved Hell Lyman alpha absorption in spectra of two QSO’s suggest that the epoch of helium ionization occurred atz≈3.Proximity zones in the spectra of the quasars(z=3.18,3.285)at 304 Å resemble Stromgren spheres, suggesting that the intergalactic medium is only singly ionized in helium. We present models of the proximity effect which include the full physics of the ionization, heating and cooling and an accurately simulated inhomogeneous gas distribution. In these models the underdense intergalactic medium is heated to at least 10,000–20,000 K after cooling to as low as a few 1000K due to cosmological expansion, with higher temperatures achieved farther away from the quasar due to absorption-hardened ionizing spectra. The quasars turn on for a few×107years with a fairly steady flux output at 228 Å comparable to the 304 Å flux output directly observed with HST. The recoveries in the spectra occur naturally due to voids in the IGM and may provide a fairly model-independent probe of the baryon density. ©1999 American Institute of Physics.