Osmium Tetroxide (OsO₄)

Heretofore unappreciated as a chemical weapon, chemists the world over were surprised when in April 2004, British intelligence officers interrupted a terrorist plot in which osmium tetroxide was to be used as an agent.

Scientists are already familiar with the use and effects of osmium tetroxide (OsO₄) even as these recent reports have introduced the general public to the compound for the first time. OsO₄ is a colorless to pale yellow solid at room temperature, occasionally called osmic acid. The solid readily evaporates at room temperature (has a high vapor pressure). An open canister left in an enclosed area would be readily noticeable based on the characteristic pungent, ozone- or chlorine-like smell. For the numerically inclined: the vapor pressure of OsO₄ is 7 mm Hg at 20°C/68°F, compared to a vapor pressure of 17 mm Hg for water, 2.10 mm Hg for sarin nerve agent (GB), and 0.0007 mm Hg for VX nerve agent (the latter three are liquids). The vapor pressure of a chemical is important in determining the inhalation hazard. Solids and liquids with no vapor pressure don't evaporate and therefore don't pose an inhalation hazard unless they are mechanically aerosolized. Liquids with very low vapor pressures, like VX nerve agent, don't evaporate readily and therefore are considered a much more significant threat for exposure via direct skin contact.

SYMPTOM(s): Lacrimation, vision disturbance, conjunctivitis; headaches; coughing, dyspnea; dermatitis

HEALTH EFFECTS: Irritation-Eye, Nose, Throat, Skin---Marked (HE14) Lung edema (HE11)

ORGAN: Eyes, respiratory system, skin