Substance profile
Osmium Tetroxide
Osmium Tetroxide is pale yellow solid; monoclinic crystals with an acrid, chlorine-like odor.
01 · Identification
What Osmium Tetroxide is
Osmium Tetroxide is pale yellow solid; monoclinic crystals with an acrid, chlorine-like odor. Its molecular formula is O4Os and its molecular weight is 254.2 g/mol. It boils at 130 °C, melts at 40.6 °C.
Under the GHS it carries the signal word Danger.
02 · Identifiers
Osmium Tetroxide identifiers and molecular data
Osmium Tetroxide CAS number and EC number
Osmium Tetroxide molecular formula and molecular weight
Other names for Osmium Tetroxide
- osmium tetraoxide
- osmic acid
03 · GHS classification
Osmium Tetroxide hazard classification
Harmonised classification under CLP Annex VI. This is the legally binding classification in the EU; other jurisdictions may differ.
Osmium Tetroxide pictograms and signal word
Osmium Tetroxide hazard class and category
| Hazard class | Category | From code | Pictogram |
|---|---|---|---|
| Acute toxicity - oral GHS chapter 3.1 | Category 1 or 2 | H300 | GHS06 |
| Acute toxicity - dermal GHS chapter 3.1 | Category 1 or 2 | H310 | GHS06 |
| Acute toxicity - inhalation GHS chapter 3.1 | Category 1 or 2 | H330 | GHS06 |
| Skin corrosion/irritation GHS chapter 3.2 | Category 1A or 1B or 1C | H314 | GHS05 |
Where two values are shown with “or”, the hazard statement is shared by more than one category or by more than one class, and the code alone does not say which. H272, for example, belongs to oxidising liquids and to oxidising solids — the physical state decides. The binding answer for a specific entry is in the CLP Annex VI table itself.
Osmium Tetroxide hazard statements (H-codes)
| Code | Hazard statement |
|---|---|
| H310 | Fatal in contact with skin. |
| H330 | Fatal if inhaled. |
| H300 | Fatal if swallowed. |
| H314 | Causes severe skin burns and eye damage. |
This page lists only the codes assigned to Osmium Tetroxide. The full reference lives on the hazard statements hub, the precautionary statements hub and the GHS pictograms hub.
Safety Data Sheet
Getting an SDS for Osmium Tetroxide
A Safety Data Sheet is written for a product, not for a substance: the supplier of the grade you actually buy issues it, so two suppliers of Osmium Tetroxide issue two different sheets. That is why there is no single authoritative SDS for a substance to download — what there is, is the job of collecting the sheets for the products you hold and keeping them current as suppliers revise them.
04 · Precautionary statements
Osmium Tetroxide precautionary statements
CLP Annex VI assigns 11 precautionary statements to Osmium Tetroxide. They are grouped the way a label groups them: what to do before handling, what to do when something has already happened, how to store it and how to dispose of it.
Prevention
What to do before and during handling so the hazard never happens.
Response
What to do once exposure, spillage or fire has already happened.
Reading the notation. … is a blank the supplier fills in — not a truncated sentence.· [square brackets] mark a part printed only when it applies.
05 · Names in the regulation
Osmium Tetroxide name in 23 EU languages
CLP Annex VI Part 3 is published in every language edition of the regulation, and the identification column is written out in each of them. Nothing below is translated by us: each line is the name as that edition prints it. Under Art. 18(2) the substance name from Annex VI is a lawful product identifier, so this is the wording to put on a label going to that market — and where the cell lists several designations, any one of them qualifies.
| Language | Name in CLP Annex VI Part 3 |
|---|---|
| Bulgarian български | осмиев тетраоксид осмиева киселина |
| Spanish español | Tetraóxido de osmio ácido ósmico |
| Czech čeština | oxid osmičelý kyselina osmičelá |
| Danish dansk | osmiumtetraoxid osmiumsyre |
| German Deutsch | Osmiumtetroxid Osmiumsäure |
| Estonian eesti | osmiumtetraoksiid osmiumhape |
| Greek ελληνικά | τετραοξείδιο του οσμίου οσμικό οξύ |
| English English | osmium tetraoxide osmic acid |
| French français | tétraoxyde d'osmium acide osmique |
| Croatian hrvatski | osmijev tetraoksid osmijeva kiselina |
| Italian italiano | tetrossido di osmio osmio tetrossido |
| Latvian latviešu | osmija tetraoksīds osmīnskābe |
| Lithuanian lietuvių | osmio tetraoksidas osmio rūgštis |
| Hungarian magyar | ozmium-tetraoxid ozmiumsav |
| Maltese Malti | tetraossidu tal-osmju aċidu osmiku |
| Dutch Nederlands | osmiumtetraoxide osmiumzuur |
| Polish polski | tetratlenek osmu tlenek osmu(VIII) |
| Portuguese português | tetróxido de ósmio ácido ósmico |
| Romanian română | tetraoxid de osmiu acid osmic |
| Slovak slovenčina | oxid osmičelý kyselina osmičelá |
| Slovenian slovenščina | osmijev tetraoksid osmijeva kislina |
| Finnish suomi | osmiumtetraoksidi osmiumhappo |
| Swedish svenska | osmiumtetraoxid osmiumsyra |
All 23 language editions of Annex VI carry this entry. Irish is the twenty-fourth official EU language and has no line here for a different reason: no consolidated CLP text has ever been published in Irish, so there is no Irish edition of Annex VI to quote a name from. Source: consolidated CLP, CELEX 02008R1272, language editions. © European Union, https://eur-lex.europa.eu — only the electronic Official Journal of the European Union is authentic.
06 · Label elements
Osmium Tetroxide GHS label elements
Everything CLP Annex VI fixes for Osmium Tetroxide, laid out the way it appears on a label. The greyed lines are the parts only the supplier can fill in.
Danger
Osmium Tetroxide
- Fatal in contact with skin.
- Fatal if inhaled.
- Fatal if swallowed.
- Causes severe skin burns and eye damage.
- Do not breathe dust/fume/gas/mist/vapours/spray.
- Do not eat, drink or smoke when using this product.
- Use only outdoors or in a well-ventilated area.
- Wear protective gloves/protective clothing/eye protection/face protection/hearing protection/…
- IF SWALLOWED:
- IF ON SKIN:
- IF INHALED:
- Immediately call a POISON CENTER/doctor/…
- Rinse mouth.
- Do NOT induce vomiting.
- Wash with plenty of water/…
Supplier name, address and telephone number· Product identifier·Nominal quantity
Need this as an actual label? Open Osmium Tetroxide in the GHS label constructor →
07 · Health hazards
Osmium Tetroxide health hazards and exposure limits
Osmium Tetroxide hazard summary
A skin and respiratory irritant, OsO4 can cause pulmonary edema in animals exposed to high concentrations. [ACGIH] A lachrymator; [ChemFinder] Tear drawing and corrosive to the skin, eyes, and respiratory tract; May cause kidney injury after prolonged or repeated exposure; [ICSC] Osmium tetroxide can cause chronic bronchitis. [LaDou, p. 382] May cause severe burns; [CAMEO] Based on animal studies, osmium tetroxide bioaccumulates after chronic exposure and may cause kidney and liver damage. [HSDB] See Osmium.
Source: Haz-Map, Information on Hazardous Chemicals and Occupational Diseases
Osmium Tetroxide occupational exposure limits
| Limit | Value | Source |
|---|---|---|
| PEL | 0.002 [mg/m3], as Os | Haz-Map, Information on Hazardous Chemicals and Occupational Diseases |
| PEL | 0.002 mg/m³ | Occupational Safety and Health Administration (OSHA) |
| PEL | TWA 0.002 mg/m3 See Appendix G | The National Institute for Occupational Safety and Health (NIOSH) |
| REL | 0.0002 ppm (0.002 mg/m³) | Occupational Safety and Health Administration (OSHA) |
| REL | 0.0006 ppm (0.006 mg/m³) | Occupational Safety and Health Administration (OSHA) |
| REL | TWA 0.002 mg/m3 (0.0002 ppm) ST 0.006 mg/m3 (0.0006 ppm) | The National Institute for Occupational Safety and Health (NIOSH) |
| IDLH | 1 mg/m3 (NIOSH, 2024) | CAMEO Chemicals |
| IDLH | 1.0 [mg/m3], as Os | Haz-Map, Information on Hazardous Chemicals and Occupational Diseases |
| IDLH | 1 mg/cu m | Hazardous Substances Data Bank (HSDB) |
These are United States values. The European Union sets its own indicative and binding limits, and the figure that applies at a given workplace is the one in the local regulation — not the one shown here.
08 · Physical and chemical properties
Osmium Tetroxide properties
Every value is shown with the conditions it was measured under and the source it came from. Where sources disagree, all values are listed rather than one being picked — the difference is usually a different form of the substance, not an error.
Osmium Tetroxide boiling point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Boiling point | 130 °C (266 °F) | NIOSH | |
| 130 °C (266 °F) | at 760 mmHg | CAMEO |
Osmium Tetroxide melting point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Melting point | 40.6 °C (105.1 °F) | HSDB | |
| 40.56 °C (105 °F) | NIOSH |
Osmium Tetroxide density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Density | 5.1 g/cm³ | Calculated | HSDB |
| 5.1 g/cm³ | NIOSH |
Osmium Tetroxide solubility
| Property | Value | Conditions | Source |
|---|---|---|---|
| Solubility | Sol in benzene, alcohol, ether, ammonium hydroxide, and phosphorus oxychloride; solubility in carbon tetrachloride @ 25 deg: 375 g/100 g | HSDB | |
| In water, 7.24 (g/100 g) at 25 °C | at 25 °C | HSDB | |
| (77 °F): 6% | at 25 °C | NIOSH |
Osmium Tetroxide vapor pressure
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor pressure | 7 mmHg | NIOSH | |
| 11 mmHg | at 27 °C | HSDB |
Osmium Tetroxide lower explosive limit (LEL)
| Property | Value | Conditions | Source |
|---|---|---|---|
| Lower explosive limit (LEL) | Noncombustible Solid | NIOSH |
Osmium Tetroxide vapor density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor density | 8.8 (air = 1) | ICSC |
Osmium Tetroxide odor threshold
| Property | Value | Conditions | Source |
|---|---|---|---|
| Odor threshold | Air odor threshhold: 0.0019 ppm v/v. Water odor threshhold: 0.012 ppm w/v (amount in water that generates the air odor threshhold in a closed system). | HSDB | |
| Odor Threshold Low: 0.0019 [mg/m3] | Haz-Map | ||
| Odor threshold from NJ "Hazardous Substance Fact Sheet" | Haz-Map |
Osmium Tetroxide critical temperature and pressure
| Property | Value | Conditions | Source |
|---|---|---|---|
| Critical temperature and pressure | 405 °C (761 °F) | HSDB |
Values compiled from PubChem Laboratory Chemical Safety Summary. Temperatures converted to Fahrenheit for reference.
09 · Fire and explosion
Osmium Tetroxide fire and explosion behaviour
These are descriptions rather than measured values, so they are kept out of the table above and quoted here with the source that reported them.
Osmium Tetroxide fire potential
Not combustible.
Source: Hazardous Substances Data Bank (HSDB)
10 · Handling and storage
Osmium Tetroxide storage and handling
Osmium Tetroxide safe storage
Separated from combustible substances, reducing agents and food and feedstuffs. Ventilation along the floor.
Source: ILO-WHO International Chemical Safety Cards (ICSCs)
Osmium Tetroxide storage conditions
Separated from combustible and reducing substances, food and feedstuffs. Ventilation along the floor.
Source: Hazardous Substances Data Bank (HSDB)
Osmium Tetroxide incompatible materials
Contact with hydrochloric acid will cause formation of poisonous chlorine gas. Contact with easily oxidized organic materials may cause fires and explosions.
Source: Hazardous Substances Data Bank (HSDB)
Osmium Tetroxide reactivity
OSMIUM TETROXIDE is incompatible with hydrochloric acid and easily oxidizes organic materials. Contact with other materials may cause fire. (NIOSH, 2024). Reacts explosively with 1-methylimidazole [J. Chem. Soc., Dalton Trans., 1979, 1084].
Source: CAMEO Chemicals
Planning storage for a mix of chemicals? Check Osmium Tetroxide in the storage compatibility matrix →
11 · Questions
Osmium Tetroxide — frequently asked questions
What is the CAS number of Osmium Tetroxide?
The CAS number of Osmium Tetroxide is 20816-12-0. Its EC number is 244-058-7.
What is the chemical formula of Osmium Tetroxide?
The molecular formula of Osmium Tetroxide is O4Os and its molecular weight is 254.2 g/mol.
What does a Osmium Tetroxide label have to show?
Under CLP Annex VI the label for Osmium Tetroxide carries the pictograms Skull and crossbones and Corrosion and the signal word is Danger.
Is Osmium Tetroxide flammable?
CLP Annex VI assigns Osmium Tetroxide no flammability hazard class. That is not a statement that it cannot burn: the harmonised list only records the hazards that were assessed for it.
Is Osmium Tetroxide a carcinogen?
CLP Annex VI records no harmonised carcinogenicity classification for Osmium Tetroxide. Annex VI is a list of agreed classifications, not a list of substances found safe, so this is an absence of a classification rather than a clean bill of health.
What is the exposure limit for Osmium Tetroxide?
The US occupational exposure limit reported for Osmium Tetroxide is 0.002 [mg/m3], as Os (Haz-Map, Information on Hazardous Chemicals and Occupational Diseases). Limits differ by country: the EU sets its own indicative and binding values, and the figure that applies at a given workplace is the one in the local regulation.
What is the boiling point of Osmium Tetroxide?
The boiling point reported for Osmium Tetroxide is 130 °C (266 °F) (NIOSH).
What is the melting point of Osmium Tetroxide?
The melting point reported for Osmium Tetroxide is 40.6 °C (105.1 °F) (HSDB).
How should Osmium Tetroxide be stored?
Separated from combustible and reducing substances, food and feedstuffs. Ventilation along the floor. (Hazardous Substances Data Bank (HSDB))
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