All but a very few instances of natural gas malfunctions (like a completely severed pipe) are safely mitigated by mixing and dilution. Most common gasses are o

All but a very few instances of natural gas malfunctions (like a completely severed pipe) are safely mitigated by mixing and dilution. Most common gasses are only dangerous in large amounts, when stratified and consentrated in a small confined space. Which is why ductless hoods are able to meet code in the first place. Ironically, this has become a bigger issue because of houses being more tightly sealed due to efficiency regulations. Old houses would naturally draw and vent in the event of any sort of out-of-equilibrium gas buildup.