Light-ion fusion reactors and high-yield target testing facilities will have a gas-filled reaction vessel. The target microexplosion will create a microfireball in this gas. The behaviour of this microfireball as it propagates and reflects from the reaction vessel wall is critical to the design of the vessel. The type of gas and the modelling assumptions used for analysis can significantly affect the prediction of this behaviour. The effects of two-temperature and multifrequency radiative transfer models are investigated for nitrogen and argon gases. The isothermal sphere model and the target X-ray attenuation model for microfireball creation are compared. The computational results are related to the analytic strong-shock theory.