Ed Sirett wrote:
Manufactured gas, aka town gas, city gas or first family gases are
extremely toxic as they contain substantial quantities of CO.

"Were" - there has been no town gas made in the UK since conversion to
natural gas was completed in 1977.

Even before then, many of the old coal gas plants had been replaced by
plants that used oil and other hydrocarbon feedstocks to produce a town
gas substitute that contained very low levels of CO. It was mostly H2
and CH4, blended with inerts to give the correct calorific value and
density to be compatible with exiting town gas burners. As with natural
gas, the smell (mercaptans) had to be added afterwards.


--
Ian White