There’s a reason these aren’t used anymore.
https://www.journals.uchicago.edu/doi/abs/10.1086/449144

Between 1963 and 1975 the annual number of suicides in England and Wales showed a sudden, unexpected decline from 5,714 to 3,693 at a time when suicide continued to increase in most other European countries. This appears to be the result of the progressive removal of carbon monoxide from the public gas supply. Accounting for more than 40 percent of suicides in 1963, suicide by domestic gas was all but eliminated by 1975.