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Osmium Tetroxide


CAS No. 20816-12-0

Osmium tetroxide (OsO₄) is a colorless, crystalline solid or pale-yellow mass with an unpleasant, acrid, chlorine-like odor. Osmium tetroxide is highly poisonous. Exposure to osmium tetroxide may cause harm to the skin, eyes, and respiratory system. Workers may be harmed from exposure to osmium tetroxide. The level of exposure depends upon the dose, duration, and work being done.

Osmium tetroxide is used in many industries. It’s used mainly as a staining agent for biological samples. Some examples of workers at risk of being exposed to osmium tetroxide include the following:

  • Lab workers who use it as a staining agent in transmission electron microscopy
  • Workers who use it to stain copolymers to show the microstructure
  • Miners who extract osmium ore

NIOSH recommends that employers use Hierarchy of Controls to prevent injuries. If you work in an industry that uses osmium tetroxide, please read chemical labels and the accompanying Safety Data Sheets for hazard information. Visit NIOSH’s page on Managing Chemical Safety in the Workplace to learn more about controlling chemical workplace exposures.

The following resources provide information about occupational exposure to osmium tetroxide. Useful search terms for osmium tetroxide include “osmic acid anhydride,” and “osmium oxide.”

NIOSH Chemical Resources

Related NIOSH Resources

  • NIOSHTIC-2 search results for osmium tetroxide—NIOSHTIC-2 is a searchable database of worker safety and health publications, documents, grant reports, and journal articles supported in whole or in part by NIOSH.
  • NIOSH Worker Health Study Summaries—NIOSH conducts research to prevent illnesses and injuries in the workplace. The NIOSH Worker Notification Program notifies workers and other stakeholders about the findings of these research studies.

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