Green: is useless already 2m next to smell almost impossible In my opinion there. Most methane clouds smell musty worse
Yellow: Exceeds so slowly the threshold of discomfort but is bearable
Red: stench under the old fish and cheese. Most are fleeing remain only the hard-boiled.
Black: pestilential stench of the toughest the tears from his eyes and lunch inflates itself again. (Risk potential for injury exists so be careful)
These are my subjective assessments I hope it could help you.
