Chlorine

[Enoughnow]

I have some pool cleaning chlorine tablets
What can I mix them with to cause death
Does pouring vinegar on them make clorine gas

 

[Jrmull1993]

Liquid ammonia cleaner and those tablets combined with being in an enclosed space would produce the fatal vapors, however it would be far from a peaceful process. Chlorine gas will burn mucous membranes such as the eyes, throat, and lungs.

Keep in mind the vapors are also explosive, so any ignition source would need to be removed.

 

[locked*n*loaded]

And keep in mind that if someone finds you in your enclosed space, they are going to be subjected to the same poison that you are. Do some research on this method. It's not the best.