  (abridged) Quantifying the ISM porosity to ionizing photons in nearby
galaxies may improve our understanding of the mechanisms leading to Lyman
Continuum photons leakage from galaxies. Primitive galaxies with low metal and
dust content have been shown to host a more patchy and porous ISM than their
high-metallicity counterparts. To what extent this peculiar structure
contributes to the leakage of ionizing photons remains to be quantitatively
studied. To address these questions we build a refined grid of models including
density-bounded regions and a possible contribution of an X-ray source. Using
MULTIGRIS, a new Bayesian code based on Monte Carlo sampling, we combine the
models as sectors under various assumptions to extract the probability density
distributions of the parameters and infer the corresponding escape fractions
from H II regions (fesc,HII). We apply this new code to a sample of 39
well-know local starbursting dwarf galaxies from the Dwarf Galaxy Survey. We
confirm previous results hinting at an increased porosity to ionizing photons
of the ISM in low-metallicity galaxies and provide, for the first time,
quantitative predictions for fesc,HII. The predicted fesc,HII for
low-metallicity objects span a large range of values, up to 60%, while the
values derived for more metal-rich galaxies are globally lower. We also examine
the influence of other parameters on the escape fractions, and find that the
specific star-formation rate correlates best with fesc,HII . Finally, we
provide observational line ratios which could be used as tracers of the photons
escaping from density-bounded regions. Although this multi-sector modelling
remains too simple to fully capture the ISM complexity, it can be used to
preselect galaxy samples with potential leakage of ionizing photons based on
current and up-coming spectral data in unresolved surveys of local and
high-redshift galaxies.
