Mixing 409 cleaner, which contains dimethyl benzyl ammonium chloride and other ingredients, with bleach can create dangerous chemical reactions, potentially releasing chlorine gas. The discussion highlights the risks of combining bleach with any other substances, emphasizing that even those with technical backgrounds may overlook these dangers. The composition of 409 includes primarily water, surfactants, and a small percentage of active ingredients, which can interact negatively with bleach. The reformulation of 409 has led to the presence of ethanolamine, which can react with bleach to form irritating gases like monochloramine and dichloramine. Overall, caution is advised when using bleach in combination with other cleaning agents due to the potential for harmful chemical reactions.