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ABRIDGED: NGC5253 is an ideal laboratory for detailed studies of starburstgalaxies. We present for the first time in a starburst galaxy a 2D study of thespatial behavior of collisional and radiative transfer effects in He^+. The HeIlines are analysed based on data obtained with FLAMES and GMOS. Collisionaleffects are negligible for transitions in the singlet cascade while relativelyimportant for those in the triplet cascade. In particular, they can contributeup to 20% of the flux in the HeIl7065 line. Radiative transfer effects areimportant over an extended and circular area of 30pc in diameter centered atthe Super Star Clusters. HeI abundance, y^+, has been mapped using extinctioncorrected fluxes of six HeI lines, realistic assumptions for T_e, n_e, and thestellar absorption equivalent width as well as the most recent emissivities. Wefound a mean of 10^3 y^+ ~80.3 over the mapped area. The relation between theexcitation and the total helium abundance, y_tot, is consistent with noabundance gradient. Uncertainties in the derivation of He abundances aredominated by the adopted assumptions. We illustrated the difficulty ofdetecting a putative He enrichment due to the presence of Wolf-Rayet stars inthe main GHIIR. Data are marginally consistent with an excess in the N/He ratioin the N enriched area of the order of both, the atmospheric N/He ratios in WRstars and the uncertainties estimated for the N/He ratios.

HeI in the central Giant HII Region of NGC 5253. A 2D observational approach to collisional and radiative transfer effects