[1] The current FDA approved sterilant gases are ethylene oxide,[2] hydrogen peroxide[3] and ozone.
[7] Thus exposure to even low levels of sterilant gas should not be treated casually and most facilities go to great lengths to adequately protect their employees.
In addition to toxicity, ethylene oxide is flammable (from above 3%)[1] and ozone is damaging to equipment not designed to resist it.
Sterilizer manufacturers go to great lengths to make their products as safe as possible but, as with any mechanical device, they can and sometimes do fail and leaks have been reported.
[8] The odor threshold for these gases is above the PELs and for ethylene oxide it is 500 ppm, approaching that of the IDLH.