Substance profile
Phosphoric acid
Phosphoric acid is unstable orthorhombic crystals or clear syrupy liquid and is odorless.
01 · Identification
What Phosphoric acid is
Phosphoric acid is unstable orthorhombic crystals or clear syrupy liquid and is odorless. Its molecular formula is H3O4P and its molecular weight is 97.995 g/mol. It boils at 407 °C, melts at 42.4 °C, is soluble in water.
Under the GHS it carries the signal word Danger. It is classed as corrosives.
02 · Identifiers
Phosphoric acid identifiers and molecular data
Phosphoric acid CAS number and EC number
Phosphoric acid molecular formula and molecular weight
Other names for Phosphoric acid
- orthophosphoric acid
- H3PO4
- C 134
- C 134 (Acid)
- C 434
- C 434 (Acid)
- Decon 4512
- Evits
- K-Etchant
- Kefo
- 3M Etching Liquid
- Mikro Klene Df
- Phosphoric Acid (Aqueous)
- Phosphoric Acid, Aqueous
- phosphoric acid ... %, orthophosphoric acid ... %
03 · GHS classification
Phosphoric acid hazard classification
Harmonised classification under CLP Annex VI. This is the legally binding classification in the EU; other jurisdictions may differ.
Phosphoric acid pictograms and signal word
Phosphoric acid hazard class and category
| Hazard class | Category | From code | Pictogram |
|---|---|---|---|
| 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.
Phosphoric acid hazard statements (H-codes)
| Code | Hazard statement |
|---|---|
| H314 | Causes severe skin burns and eye damage. |
This page lists only the codes assigned to Phosphoric acid. 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 Phosphoric acid
Our own Phosphoric acid safety data sheet walks through all sixteen sections of the published data. What it is not is the document an inspector asks for: an SDS is issued for a product by its supplier, so the sheet covering the grade actually standing in your store exists only in that supplier’s version. Collecting those and keeping them current as suppliers revise them is a separate job.
04 · Precautionary statements
Phosphoric acid precautionary statements
CLP Annex VI assigns 5 precautionary statements to Phosphoric acid. 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
Phosphoric acid 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 | фосфорна киселина . %, ортофосфорна киселина . % |
| Spanish español | Ácido fosfórico al … % ácido ortofosfórico al … % |
| Czech čeština | kyselina fosforečná … %, kyselina orthofosforečná … % |
| Danish dansk | phosphorsyre …% orthophosphorsyre … % |
| German Deutsch | Phosphorsäure …%, ortho -Phosphorsäure …% |
| Estonian eesti | fosforhape … %, ortofosforhape … % |
| Greek ελληνικά | φωσφορικό οξύ . %, ορθοφωσφορικό οξύ . % |
| English English | phosphoric acid . %, orthophosphoric acid . % |
| French français | acide phosphorique à … %, acide orthophosphorique à … % |
| Croatian hrvatski | fosforna kiselina %, ortofosforna kiselina % |
| Italian italiano | acido fosforico …% acido ortofosforico …% |
| Latvian latviešu | fosforskābe …%, ortofosforskābe … % |
| Lithuanian lietuvių | …% fosforo rūgštis, …% ortofosforo rūgštis |
| Hungarian magyar | foszforsav … %, ortofoszforsav … % |
| Maltese Malti | aċidu fosforiku. %, aċidu ortofosforiku. % |
| Dutch Nederlands | fosforzuur . %, orthofosforzuur . % |
| Polish polski | This edition has a typographic error here. The Polish edition prints "kwas ortofosorowy" — the letter f is missing from "ortofosforowy". Regulation (EU) 2018/669, OJ L 115, 4.5.2018, p. 42 kwas fosforowy(V) … %, kwas ortofosorowy … % |
| Portuguese português | ácido fosfórico a ... % ácido ortofosfórico a ... % |
| Romanian română | acid fosforic . %, acid ortofosforic . % |
| Slovak slovenčina | kyselina fosforečná %, kyselina trihydrogenfosforečná % |
| Slovenian slovenščina | fosforjeva kislina . %, ortofosforjeva kislina . % |
| Finnish suomi | fosforihappo… % ortofosforihappo… % |
| Swedish svenska | fosforsyra %, ortofosforsyra % |
One or more lines above are flagged. In those language editions the Regulation as published in the Official Journal prints something that the rest of the same row contradicts — a name belonging to a different entry, or the qualifier of a paired entry. Each flag cites the amending act and the Official Journal page, so the wording can be checked at source. The lines are reproduced as printed, because Art. 18(2) points at Annex VI and not at our reading of it; the note beside each one says what the row’s own EC and CAS numbers identify.
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
Phosphoric acid GHS label elements
Everything CLP Annex VI fixes for Phosphoric acid, laid out the way it appears on a label. The greyed lines are the parts only the supplier can fill in.
Danger
Phosphoric acid
- Causes severe skin burns and eye damage.
- Do not breathe dust/fume/gas/mist/vapours/spray.
- Wear protective gloves/protective clothing/eye protection/face protection/hearing protection/…
- IF SWALLOWED:
- Immediately call a POISON CENTER/doctor/…
- Do NOT induce vomiting.
Supplier name, address and telephone number· Product identifier·Nominal quantity
Need this as an actual label? Open Phosphoric acid in the GHS label constructor →
07 · Health hazards
Phosphoric acid health hazards and exposure limits
Phosphoric acid hazard summary
Liquid or solid form causes second degree burns after contact for a few minutes; [CHRIS] Usually shipped as a solid or 85% solution. [CAMEO] Phosphoric acid > 70% is corrosive to skin. [Quick CPC] Phosphoric acid is an eye, skin, and upper respiratory tract irritant. [ACGIH] The risk of pulmonary edema is very small. [Desai H. Phosphorus and Phosphorus Compounds. In: Sullivan JB, Krieger GR (eds). Hazardous Materials Toxicology. Baltimore: Williams & Wilkins, 1992; p. 938.] Corrosive to the skin, eye, and respiratory tract; [ICSC] If phosphoric acid is used as a catalyst, phosphine can be formed in the strongly reducing atmosphere of the hot emissions. In air, phosphine rapidly oxidizes to phosphorus oxide. [IARC 2012: Iron and steel founding]
Source: Haz-Map, Information on Hazardous Chemicals and Occupational Diseases
Phosphoric acid occupational exposure limits
| Limit | Value | Source |
|---|---|---|
| PEL | 1.0 [mg/m3] | Haz-Map, Information on Hazardous Chemicals and Occupational Diseases |
| PEL | 1 mg/m³ | Occupational Safety and Health Administration (OSHA) |
| PEL | TWA 1 mg/m3 See Appendix G | The National Institute for Occupational Safety and Health (NIOSH) |
| REL | 1 mg/m³ | Occupational Safety and Health Administration (OSHA) |
| REL | 3 mg/m³ | Occupational Safety and Health Administration (OSHA) |
| REL | TWA 1 mg/m3 ST 3 mg/m3 | The National Institute for Occupational Safety and Health (NIOSH) |
| IDLH | 1000 mg/m3 (NIOSH, 2024) | CAMEO Chemicals |
| IDLH | 1000.0 [mg/m3] | Haz-Map, Information on Hazardous Chemicals and Occupational Diseases |
| IDLH | 1000 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
Phosphoric acid 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.
Phosphoric acid boiling point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Boiling point | 407 °C (764.6 °F) | HSDB | |
| 212.78 °C (415 °F) | NIOSH | ||
| 158 °C (316.4 °F) | ICSC |
Phosphoric acid melting point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Melting point | 42.4 °C (108.3 °F) | HSDB | |
| -17.5 °C (0.5 °F) | HSDB | ||
| 25 °C (77 °F) | HSDB |
Phosphoric acid density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Density | 1.8693 g/cm³ | HSDB | |
| 1.8741 g/cm³ | at 25 °C | HSDB | |
| 25 g/cm³ | at 25 °C | HSDB |
Phosphoric acid solubility
| Property | Value | Conditions | Source |
|---|---|---|---|
| Solubility | Soluble in water, alcohol; soluble in 8 volumes of 3:1 ether:alcohol mixture | HSDB | |
| Soluble in ethanol | HSDB | ||
| 548 g/100 g water at 20 °C | at 20 °C | HSDB |
Phosphoric acid vapor pressure
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor pressure | 0.03 mmHg | NIOSH | |
| 0.0285 mmHg | at 20 °C | HSDB |
Phosphoric acid autoignition temperature
| Property | Value | Conditions | Source |
|---|---|---|---|
| Autoignition temperature | Not flammable (USCG, 1999) | CAMEO |
Phosphoric acid lower explosive limit (LEL)
| Property | Value | Conditions | Source |
|---|---|---|---|
| Lower explosive limit (LEL) | Noncombustible Solid | NIOSH |
Phosphoric acid vapor density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor density | 3.4 (air = 1) | ICSC |
Phosphoric acid corrosivity
| Property | Value | Conditions | Source |
|---|---|---|---|
| Corrosivity | Corrosive to ferrous metals and alloys | HSDB |
Values compiled from PubChem Laboratory Chemical Safety Summary. Temperatures converted to Fahrenheit for reference.
09 · Fire and explosion
Phosphoric acid 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.
Phosphoric acid fire potential
Not combustible.
Source: Hazardous Substances Data Bank (HSDB)
10 · Handling and storage
Phosphoric acid storage and handling
Phosphoric acid reactive group
CAMEO Chemicals places Phosphoric acid in the reactive group Acids, Weak. Compatibility with other chemicals is worked out from the group, not from the individual substance — which is why two substances you have never seen react can still be flagged as a pair that must be separated.
A reactive group is a CAMEO Chemicals (US NOAA) grouping, not a GHS hazard class: it has no code, no category and no legal force. It is what the storage compatibility matrix on this site computes from.
Phosphoric acid safe storage
Dry. Well closed. Separated from food and feedstuffs and incompatible materials. See Chemical Dangers. Store in an area without drain or sewer access.
Source: ILO-WHO International Chemical Safety Cards (ICSCs)
Phosphoric acid storage conditions
Store in cool, dry, well-ventilated location. Separate from alkalies and most metals.
Source: Hazardous Substances Data Bank (HSDB)
Phosphoric acid incompatible materials
Reacts with metals to liberate flammable hydrogen gas.
Source: Hazardous Substances Data Bank (HSDB)
Phosphoric acid reactivity
PHOSPHORIC ACID reacts exothermically with bases. May react with active metals, including such structural metals as aluminum and iron, to release hydrogen, a flammable gas. Can initiate the polymerization of certain classes of organic compounds. Reacts with cyanide compounds to release gaseous hydrogen cyanide. May generate flammable and/or toxic gases in contact with dithiocarbamates, isocyanates, mercaptans, nitrides, nitriles, sulfides, and strong reducing agents. Forms explosive mixture with nitromethane. Reacts violently with sodium tetrahydroborate. In the presence of chlorides can corrode stainless steel to form explosive hydrogen gas. Emits toxic and irritating fumes of oxides of phosphorus when heated to decomposition [Lewis, 3rd ed., 1993, p. 1029].
Source: CAMEO Chemicals
Planning storage for a mix of chemicals? Check Phosphoric acid in the storage compatibility matrix →
11 · Transport
Phosphoric acid UN number and transport classification
Transport classification is a separate system from the GHS classification above. It decides how a package is marked and how a load may be carried; it does not follow from the workplace label, and the workplace label does not follow from it. The entries below are linked by CAS number, never by name.
The same CAS number is shipped under more than one UN number. Which entry applies follows from the form and the concentration of the consignment — read the proper shipping name, not the CAS.
Phosphoric acid under UN 1805 — shipping name, class and packing group
Europe · ADR 2025, Table A
| Proper shipping name (3.1.2) | Class | Classification code | PG | Labels (column 5) |
|---|---|---|---|---|
| PHOSPHORIC ACID, SOLUTION | 8 | C1 | III | |
Source: ADR 2025, Table A of Chapter 3.2 · ECE/TRANS/352 Vol. I (UNECE). Class 8 is “Corrosive substances” (ADR 2.1.1.1).
United States · 49 CFR 172.101 Hazardous Materials Table
| Proper shipping name (column 2) | Class or division | PG | Labels (column 6) |
|---|---|---|---|
| Phosphoric acid solution | 8 | III | |
Source: 49 CFR 172.101 Hazardous Materials Table · eCFR, revision 2026-08-03. Class 8 is “Corrosive material” (49 CFR 173.2).
Phosphoric acid under UN 3453 — shipping name, class and packing group
Europe · ADR 2025, Table A
| Proper shipping name (3.1.2) | Class | Classification code | PG | Labels (column 5) |
|---|---|---|---|---|
| PHOSPHORIC ACID, SOLID | 8 | C2 | III | |
Source: ADR 2025, Table A of Chapter 3.2 · ECE/TRANS/352 Vol. I (UNECE). Class 8 is “Corrosive substances” (ADR 2.1.1.1).
United States · 49 CFR 172.101 Hazardous Materials Table
| Proper shipping name (column 2) | Class or division | PG | Labels (column 6) |
|---|---|---|---|
| Phosphoric acid, solid | 8 | III | |
Source: 49 CFR 172.101 Hazardous Materials Table · eCFR, revision 2026-08-03. Class 8 is “Corrosive material” (49 CFR 173.2).
12 · Questions
Phosphoric acid — frequently asked questions
What is the CAS number of Phosphoric acid?
The CAS number of Phosphoric acid is 7664-38-2. Its EC number is 231-633-2.
What is the chemical formula of Phosphoric acid?
The molecular formula of Phosphoric acid is H3O4P and its molecular weight is 97.995 g/mol.
What does a Phosphoric acid label have to show?
Under CLP Annex VI the label for Phosphoric acid carries the pictogram Corrosion and the signal word is Danger.
Is Phosphoric acid flammable?
CLP Annex VI assigns Phosphoric acid 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 Phosphoric acid a carcinogen?
CLP Annex VI records no harmonised carcinogenicity classification for Phosphoric acid. 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 Phosphoric acid?
The US occupational exposure limit reported for Phosphoric acid is 1.0 [mg/m3] (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 Phosphoric acid?
The boiling point reported for Phosphoric acid is 407 °C (764.6 °F) (HSDB).
What is the melting point of Phosphoric acid?
The melting point reported for Phosphoric acid is 42.4 °C (108.3 °F) (HSDB).
How should Phosphoric acid be stored?
Store in cool, dry, well-ventilated location. Separate from alkalies and most metals. (Hazardous Substances Data Bank (HSDB))
Nearby
Substances next to Phosphoric acid
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