You aren't guaranteed to die from being shot in the head either. However there are things which the medical community recognizes have no safe level of exposure.

From the original article: "The toxicity of benzene in humans has been well established for over 120 years. The hematotoxicity of benzene has been described as early as 1897. A study from 1939 on benzene stated that “exposure over a long period of time to any concentration of benzene greater than zero is not safe,” which is a comment reiterated in a 2010 review of benzene research specifically stating “There is probably no safe level of exposure to benzene, and all exposures constitute some risk in a linear, if not supralinear, and additive fashion.”