Argon Gas
In May, 1983, Charlotte Huddelston died after breathing argon gas mistakenly pumped into the oxygen system at Fort McLellans Noble Army Hospitalmaking her the third victim of the mix-up.
Apparently the five-foot white tank of odorless, nontoxic argon resembled those that usually contained oxygen. Although the argon didnt poison anyone, it displaced the oxygen supply and suffocated its victims.