  This paper outlines a way to determine the ICF using only infrared data. We
identify four line pairs, [NeIII] 36$\micron$/[NeII] 12.8$\micron$,
[NeIII]~15.6$\micron$ /[NeII] 12.8$\micron$, [ArIII] 9$\micron$/[ArII]
6.9$\micron$, and [ArIII] 21$\micron$/[ArII] 6.9$\micron$, that are sensitive
to the He ICF. This happens because the ions cover a wide range of ionization,
the line pairs are not sensitive to electron temperature, they have similar
critical densities, and are formed within the He$^+$/H$^+$ region of the
nebula. We compute a very wide range of photoionization models appropriate for
galactic HII regions. The models cover a wide range of densities, ionization
parameters, stellar temperatures, and use continua from four very different
stellar atmospheres.
  The results show that each line pair has a critical intensity ratio above
which the He ICF is always small. Below these values the ICF depends very
strongly on details of the models for three of the ratios, and so other
information would be needed to determine the helium abundance. The [Ar III]
9$\micron$/[ArII] 6.9$\micron$ ratio can indicate the ICF directly due to the
near exact match in the critical densities of the two lines. Finally, continua
predicted by the latest generation of stellar atmospheres are sufficiently hard
that they routinely produce significantly negative ICFs.
