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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

Logo of NIOSH Pocket Guide

NIOSH Pocket Guide

The NIOSH Pocket Guide to Chemical Hazards (NPG) helps workers, employers, and occupational health professionals recognize and control workplace chemical hazards.

Logo of Manual of Analytical Methods.

Manual of Analytical Methods

The NIOSH Manual of Analytical Methods (NMAM) is a collection of methods for sampling and analysis of contaminants in workplace air, and in the blood and urine of workers who are occupationally exposed.

Logo of Health Hazard Evaluations consisting of three letters: HHE

Health Hazard Evaluations

The Health Hazard Evaluation Program (HHE) conducts onsite investigations of possible worker exposure to chemicals. Search the HHE database for more information on osmium tetroxide.

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.

Selected Publications

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International Resources