Spectroscopy Of Low Metallicity Giant H II Regions: A grid of low   Metallicity Stellar atmospheres
  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. 
S.L. Pistinner, P. H. Hauschildt, D. Eichler, & E. A. Baron