Tenants complaining of vent hood not going outside

[ksmith96]

My tenants have recently started to complain that their house gets smoky when they cook because the vent hood on the oven doesn't vent to the outside. What would you do about this issue. Their communication to me is that "the CO2 detectors keep going off and I know that it's because the fan blows all the fumes in the the house which is why our walls are covered in soot when we moved in." They also state "I was going to go to the fire department and have them test our house for CO2 poisoning. Have you dealt with this issue and what was the remedy?

[Kassandra RPM Alaska]

Anytime they complain "healthy and safety" I always get it checked out by a pro and then decide what to do next.