  To place meaningful constraints on Big Bang Nucleosynthesis models, the
primordial helium abundance determination is crucial. Low-metallicity HII
regions have been used to estimate it since their statistical uncertainties are
relatively small. We present a new determination of the primordial helium
abundance, based on long slit spectra of the HII region NGC 346 in the small
Magellanic cloud. We obtained spectra using three $409'' \times 0.51''$ slits
divided in 97 subsets. They cover the range $\lambda\lambda3600-7400$ of the
electromagnetic spectrum. We used PyNeb and standard reduction procedures to
determine the physical conditions and chemical composition. We found that for
NGC 346: $X=0.7465$, $Y=0.2505$ and $Z=0.0030$. By assuming $\Delta Y / \Delta
O = 3.3\pm0.7$ we found that the primordial helium abundance is $Y_{\rm P}=
0.2451 \pm 0.0026$ (1$\sigma$). Our $Y_{\rm P}$ value is in agreement with the
value of neutrino families, $N_{\nu}$, and with the neutron half-life time,
$\tau_{n}$, obtained in the laboratory.
