To place meaningful constraints on Big Bang Nucleosynthesis models , the primordial helium abundance determination is crucial .
Low-metallicity H ii 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 H ii region NGC 346 in the small Magellanic cloud .
We obtained spectra using three 409 ^ { \prime \prime } \times 0.51 ^ { \prime \prime } slits divided in 97 subsets .
They cover the range \lambda \lambda 3600 - 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 \pm 0.7 we found that the primordial helium abundance is Y _ { P } = 0.2451 \pm 0.0026 ( 1 \sigma ) .
Our Y _ { 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 .