Osmium Tetroxide (OsO4), a severe oxidizer, is highly poisonous even at low exposure levels. It must be handled with appropriate precautions. In particular, inhalation at concentrations well below those at which a smell can be perceived, can lead to pulmonary edema, and subsequent death. Osmium tetroxide is regarded as a substance with poor warning properties, and noticeable symptoms can take hours to appear after exposure. OsO4 also stains the human cornea, which can lead to blindness if proper safety precautions are not observed.

Prior to using OsO4, the PI must ensure that all students and laboratory workers receive specific instruction regarding the hazards of osmium tetroxide as described in Section VII (1.1.4.) of the Chemical Hygiene Plan (Laboratory Safety Handbook).

Control Measures

  • Osmium tetroxide solutions must be prepared and handled in a certified fume hood.
  • Choose a hood with minimal equipment or obstructions to ensure good capture and exhaust of vapors.
  • Working surfaces should be protected with plastic backed absorbent pads to insure containment of any spills.
  • Post a warning sign on the hood to alert others to that osmium tetroxide is present. The sign should include the hazards of osmium. The Emergency Information Card posted in the hall at the entrance to the lab should also reflect the use of this material.
  • Ensure that the safety shower and eyewash unit are operational, and access is unblocked.

Personal Protective Equipment (PPE)

The following minimum PPE must be worn when working with pure osmium tetroxide and concentrated solutions:

  • Splash proof chemical safety goggles (safety glasses alone are not adequate protection because of osmium tetroxide’s severe effects on the eyes).
  • Disposable nitrile gloves (NOT latex). Double-gloving is recommended when working with pure osmium tetroxide or concentrated solutions. Change gloves frequently and when contaminated, punctured or torn. Wash hands immediately after removing gloves.
  • Standard or disposable laboratory coat or disposable coveralls, buttoned and with the sleeves rolled down. A standard laboratory coat may be reused before laundering if it has not been contaminated with osmium tetroxide. If a garment is contaminated, remove, place in chemical hood, and decontaminate with corn oil or aqueous solutions of sodium sulfide or sodium sulfite before disposing of as hazardous waste or laundering.

Safe Use Procedures

  • Because of its high acute toxicity and powerful oxidizing ability, Osmium tetroxide must be handled using prudent practices. In particular, all work with osmium tetroxide must be conducted in a fume hood to prevent exposure by inhalation, and personal protective equipment (see above) must be worn at all times to prevent eye and skin contact.
  • Osmium tetroxide should be purchased as a liquid to avoid particulate exposure from the powdered form. The solutions should be stored in labeled tightly sealed containers, and these should be placed in secondary containment.
  • Secondary containment should be used anytime the material is transported to another lab location.
  • When osmium tetroxide is freshly prepared and active, it is colorless to pale yellow in color. When the material reacts and causes oxidation, it turns black. This is helpful to know, especially in the event of a splash or spill or inadvertent dermal exposure (black dots will appear on the skin).
  • When moving pure osmium tetroxide to a chemical hood, do not remove it from the secondary containment until it is in the hood.
    Prepare the smallest amount of solution necessary for the procedure, typically 50 ml or less. Prepare the solution volumetrically rather than gravimetrically. If a balance must be used, weighing must take place in the chemical hood.
    Pure osmium tetroxide or its concentrated solutions must be opened only in a chemical hood that has been certified within the last 12 months. During use, the sash must be lowered to operating height.
  • All labware that has contacted osmium tetroxide must be decontaminated by rinsing or dipping in corn oil or aqueous solutions of sodium sulfide or sodium sulfite before removing from the hood.
  • Immediately after working with osmium tetroxide, decontaminate any spills with kitty litter soaked with corn oil. Dispose of contaminated kitty litter as hazardous waste.
  • Wipe down the area with aqueous solutions of sodium sulfide or sodium sulfite.


In the event of a spill, take appropriate actions to prevent exposure of osmium to everyone in the room, and to avoid the spread of contamination. If the spill is small and manageable (less than 2 ml), lab personnel will:

  • Alert personnel in the immediate area.
  • Isolate the area to prevent the spread of contamination.
  • Don appropriate PPE (At a minimum, double gloves, buttoned lab coat and safety goggles).
  • Cover the spill with inert absorbent (Speedi-Dri”, or kitty litter) that has been infused with vegetable oil (corn oil is preferred).
  • Scoop the contaminated material up and place it in a glass or plastic container (jar or pail) with a tight fitting lid. The Director of EH&S can assist in obtaining an appropriate waste container.
  • Wash the area with an aqueous solution of sodium sulfite.
  • Clean the area again with detergent solution.
  • Remove contaminated PPE carefully and place it in the waste container.
  • Label the container with a properly completed hazardous waste label, and transport to the 180-Day Hazardous Waste Storage Area.
  • Notify the Director of EH&S (Chemical Hygiene Officer).

When the quantity spilled is greater than 2 ml, lab personnel will:

  • Evacuate the area, and close all doors leading to lab upon exiting.
  • Place a sign stating “OSMIUM TETROXIDE SPILL; DO NOT ENTER” on the door to warn others of the spill.
  • Call Campus Safety, who will request assistance from the NLFD Hazardous Materials Response Team.
  • Notify the Director of EH&S (Chemical Hygiene Officer)

Personnel Exposure

  • Immediately seek medical attention for any exposure.
  • Skin exposure: Flush exposed skin with water for at least 15 minutes while removing any contaminated clothing.
  • Eye exposure: Flush eyes with water for at least 15 minutes. Affected individuals may need help holding their eyes open under water.
  • Inhalation exposures: If osmium tetroxide vapor has been inhaled from a spill, move the victim to fresh air immediately.

Handling and Storage Procedures

Pure osmium tetroxide and concentrated solutions should be stored in a location that is secure to unauthorized access, such as a locked cabinet, or a refrigerator within a laboratory that is locked when authorized personnel are not present. A refrigerator containing osmium tetroxide must be labeled with a caution sign noting the presence of osmium tetroxide and its hazards.

Store pure osmium tetroxide and its concentrated solutions in appropriate, sealed glass containers within unbreakable secondary containment (i.e., a bottle or vial within a sealed compatible plastic jar or metal can with lid). Label all containers, including secondary containment, with the chemical name and hazard warning.

Neutralizing Osmium Tetroxide

To reduce hazards involved in discarding osmium tetroxide, the following neutralization procedure should be used:

  • A 2% solution of osmium tetroxide can be fully neutralized by twice its volume of vegetable oil (corn oil is preferred because of its high percentage of unsaturated bonds). For every 10 ml of 2% osmium tetroxide solution, 20 ml of corn oil is required. Pour the corn oil into the osmium tetroxide solution and wait for the oil to completely turn black.
  • To test if osmium tetroxide is fully neutralized, hold a piece of filter paper soaked in corn oil over the solution. Blackening indicates that osmium tetroxide is still present and more corn oil should be added.
  • Aqueous solutions contaminated with osmium tetroxide can be fully neutralized by adding sodium sulfide or sodium sulfite to reduce osmium tetroxide to less hazardous forms.
  • Dispose of neutralized solutions as hazardous waste.