We present results of non-volcanic-gas (CO₂) hazard assessment at the Mefite d’Ansanto area (Italy) where a cold-gas stream, which has already been lethal to humans and animals, forms in the valleys surrounding the emission zone. We took the uncertainty related to the gas emission and meteorological conditions into account. Results include maps of CO₂ concentrations at defined probability levels and the probability of overcoming specified CO₂ concentrations over specified time intervals.