For those who tried Carbon Monoxide and it didn't work. Did you try again?

[persef]

Of all the methods I could use, I found this to be the method with the "most peaceful" passage. I tried to find reports of people who tried this method with charcoal and it didn't work. Compared to other methods, I thought that few people failed the CO method. I would like to hear from people on the forum who tried it and it didn't work. Why do you think it didn't work? And would you try this method again?