  We calculate a grid of spherically symmetric OB stellar atmospheres at low
metallicities, including both non-local thermodynamic equilibrium (NLTE) and
metal line blanketing effects. This is done to assess the uncertainties in
helium abundance determination by nebular codes due to input stellar atmosphere
models. The more sophisticated stellar atmosphere models we use can differ from
LTE models by as much as 40 percent in the ratio of He to H-ionizing photons.
