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CHEMINFO Record Number: 99
CCOHS Chemical Name: Phosphoric acid solutions

Orthophosphoric acid
o-Phosphoric acid
White phosphoric acid
Phosphoric acid (non-specific name)

Chemical Name French: Acide phosphorique solutions
Chemical Name Spanish: Acido fosfórico
CAS Registry Number: 7664-38-2
UN/NA Number(s): 1805
RTECS Number(s): TB6300000
EU EINECS/ELINCS Number: 231-633-2
Chemical Family: Phosphorus and compounds / inorganic acid / mineral acid / phosphorus oxo acid
Molecular Formula: H3-O4-P
Structural Formula: (HO)3-P=O


Appearance and Odour:
Clear, colourless, syrupy liquid (75-85% solution); odourless (10,11,12).

Odour Threshold:
Not applicable. Odourless.

Warning Properties:
POOR - No odour warning properties.

Phosphoric acid is available in aqueous solution in concentrations ranging from 33 to 85 percent, with 75, 80 and 85% being the most common. Pure anhydrous phosphoric acid forms a hemihydrate (CAS 16271-20-8).

Uses and Occurrences:
Used in the manufacture of phosphate fertilizers and salts, superphosphates, polyphosphates, soaps and detergents, pharmaceuticals, activated carbon, animal feed, ceramics, dental cements, soft drinks, gelatin, food additives, rust inhibitors, fire-control agents, waxes and polishes, water treatment chemicals; acidulant and flavour agent; sequestering, metal complexing and stabilizing agent in food processing; bonding agent in refractory products; in electropolishing, lithography and photoengraving, printing, metal cleaning and sugar refining; in acidic hard-surface cleaning and sanitation formulations; wood and fabric flameproofing; opacity control in glass manufacture; textile dyeing; boiler cleaning; rubber latex coagulation; catalyst; laboratory reagent.(8,9,10,11)


Clear, colourless, odourless, viscous, syrupy liquid (75-85% aqueous solution). Will not burn. Can decompose at high temperatures forming toxic phosphorus oxides. Certain chemical reactions can liberate hazardous gases. Contact with metals liberates flammable hydrogen gas. CORROSIVE to the eyes, skin and respiratory tract. Can cause blindness and permanent scarring.


Effects of Short-Term (Acute) Exposure

Phosphoric acid solutions have low vapour pressures at room temperature and are not expected to present an inhalation hazard unless a mist is generated. Mists can probably cause irritation of the nose, throat and respiratory tract.
A mechanic aboard a ship transporting 4000 tons of phosphoric acid was apparently exposed to phosphoric acid vapours three times for 20 minutes/exposure while attempting to repair a leak. Weakness, dry cough, chest pain and shortness of breath developed 7 to 8 hours after exposure. This worker still experienced symptoms of reactive airways dysfunction a year after the exposure. A co-worker with similar exposure died due to acute respiratory failure.(1) The circumstances of the exposure are not well-defined and it is not known if the phosphoric acid was heated (for example by welding) while the workers were trying to repair the leak. Toxic phosphorus oxides can form upon heating phosphoric acid.

Skin Contact:
The degree of irritation caused by phosphoric acid depends upon the concentration of the solution and the duration of contact. Concentrated solutions can cause corrosive tissue injury or severe burns, based on animal information. Dilute solutions can probably cause mild to moderate irritation. There is no human information available.

Eye Contact:
The degree of irritation caused by phosphoric acid depends upon the concentration of the solution and the duration of contact. Concentrated solutions can cause severe burns and permanent eye damage, based on animal information. Mists may cause eye irritation. There is no human information available.

There are no reports of occupational ingestion of phosphoric acid. There is one case report of an individual who died 19 days after ingesting an unspecified amount and concentration of phosphoric acid. Death was due to internal bleeding. Tissue death (necrosis) of the upper and lower digestive tract and the pancreas was evident at autopsy.(2) Ingestion is not a typical route of occupational exposure.

Effects of Long-Term (Chronic) Exposure

SKIN: Repeated or prolonged contact may result in dermatitis (dry, red skin).

INHALATION: Pulmonary function was studied in a group of 131 phosphorus refinery workers employed for 3 to 46 years. Typical exposures included phosphoric acid, phosphorus oxides, fluorides and coal tar pitch volatiles. Airborne levels of phosphoric acid were not measured. No significant changes in pulmonary function were observed, once the effects of smoking on lung function were controlled.(3) However, no conclusions can be drawn from this study due to limitations such as lack of exposure information and concurrent exposure to other chemicals.


There is no human or animal information available.

The International Agency for Research on Cancer (IARC) has not evaluated the carcinogenicity of this chemical.

The American Conference of Governmental Industrial Hygienists (ACGIH) has not assigned a carcinogenicity designation to this chemical.

The US National Toxicology Program (NTP) has not listed this chemical in its report on carcinogens.

Teratogenicity and Embryotoxicity:
There is no human or animal information available.

Reproductive Toxicity:
There is no human or animal information available.

There are no reports of mutagenicity in humans or human cell cultures. Negative results have been obtained in bacteria.

Toxicologically Synergistic Materials:
There is no information available.

Potential for Accumulation:
Phosphoric acid can be absorbed into the body and enters the phosphate pool. Inorganic phosphate ion is naturally found in the body. It is excreted mainly in the urine.(8,9)


Remove source of contamination or move victim to fresh air. Obtain medical attention immediately.

Skin Contact:
Avoid direct contact with this chemical. Wear chemical protective gloves, if necessary. As quickly as possible, flush contaminated area with lukewarm, gently running water for at least 20-30 minutes, by the clock. If irritation persists, repeat flushing. DO NOT INTERRUPT FLUSHING. If necessary, keep emergency vehicle waiting. Under running water, remove contaminated clothing, shoes, and leather goods (e.g., watchbands, belts). Transport victim to an emergency care facility immediately. Completely decontaminate clothing, shoes and leather goods before re-use or discard.

Eye Contact:
Avoid direct contact with this chemical. Wear chemical protective gloves, if necessary. Immediately flush the contaminated eye(s) with lukewarm, gently flowing water for at least 20-30 minutes, by the clock, while holding the eyelid(s) open. Neutral saline solution may be used as soon as it is available. DO NOT INTERRUPT FLUSHING. If necessary, keep emergency vehicle waiting. Take care not to rinse contaminated water into the non-affected eye or onto the face. If irritation persists repeat flushing. Quickly transport victim to an emergency care facility.

NEVER give anything by mouth if victim is rapidly losing consciousness, or is unconscious or convulsing. Have victim rinse mouth thoroughly with water. DO NOT INDUCE VOMITING. Have victim drink 240 to 300 mL (8 to 10 oz.) of water to dilute material in stomach. If milk is available, it may be administered AFTER the water has been given. If vomiting occurs naturally, repeat administration of water. Quickly transport victim to an emergency facility.

First Aid Comments:
Provide general supportive measures (comfort, warmth, rest). Consult a doctor and/or the nearest Poison Control Centre for all exposures except minor instances of inhalation or skin contact.
All first aid procedures should be periodically reviewed by a doctor familiar with the material and its condition of use in the workplace.


Flash Point:
Not combustible (will not burn).

Lower Flammable (Explosive) Limit (LFL/LEL):
Not applicable

Upper Flammable (Explosive) Limit (UFL/UEL):
Not applicable

Autoignition (Ignition) Temperature:
Not applicable

Sensitivity to Mechanical Impact:
Not sensitive. Stable compound.

Sensitivity to Static Charge:
Not sensitive. Electrical conductivity of aqueous phosphoric acid is very high (1.4 x 10(21) pS/m).(12)

Combustion and Thermal Decomposition Products:
Phosphorus oxides

Fire Hazard Summary:
Phosphoric acid does not burn. It can react with most metals to produce highly flammable hydrogen gas, that may explode if ignited. During a fire, irritating/toxic phosphorus oxides may be generated. Containers may explode in the heat of a fire.

Extinguishing Media:
This material does not burn. Extinguish fire using appropriate extinguishing media for the surrounding fire.(14)

Fire Fighting Instructions:
Evacuate area and fight fire from a safe distance or a protected location. Approach fire from upwind.
If possible, isolate materials not involved in the fire and protect personnel. Containers may explode in the heat of the fire. Move containers from fire area if it can be done without risk. Otherwise, use water in flooding quantities as a spray or fog to keep fire-exposed containers cool and absorb heat. Apply water, as an extinguishant or as a coolant, from as far a distance as possible.
Phosphoric acid and its decomposition products are hazardous to health. Do not enter without wearing specialized protective equipment suitable for the situation. Firefighter's normal protective equipment (Bunker Gear) will not provide adequate protection. Chemical resistant clothing (e.g. chemical splash suit and positive pressure self-contained breathing apparatus (MSHA/NIOSH approved or equivalent) may be necessary.


NFPA - Health: 3 - Short exposure could cause serious temporary or residual injury.
NFPA - Flammability: 0 - Will not burn under typical fire conditions.
NFPA - Instability: 0 - Normally stable, even under fire conditions, and not reactive with water.


Molecular Weight: 98.0

Conversion Factor:
Not applicable

Physical State: Liquid
Melting Point: 21 deg C (70 deg F) (85% solution); -17.5 deg C (0.5 deg F) (75%) (Freezing point) (10,15)
Boiling Point: 158 deg C (316 deg F) (85% solution); 135 deg C (275 deg F) (75%) (water boils off) (10)
Relative Density (Specific Gravity): 1.685 (85% solution); 1.573 (75%) at 25 deg C (water=1) (10,11)
Solubility in Water: Soluble in all proportions.(15,16)
Solubility in Other Liquids: Soluble in ethanol (8,9,11)
Coefficient of Oil/Water Distribution (Partition Coefficient): Not available
pH Value: 1.5 (0.1N H3PO4); 2.0-2.2 (1%) (8)
Acidity: Medium-strong, tribasic acid. pKa1 = 2.15 (K1 = 7.1 x 10(-3)); pKa2 = 7.2 (K2 = 6.3 x 10(-8)); pKa3 = 12.36 (K3 = 4.4 x 10(-13)) (10,15)
Viscosity-Dynamic: 140 mPa.s (140 centipoises) (100%); 28 mPa.s (20 centipoises) (85%); 15 mPa.s (15 centipoises) (75%) at 20 deg C (10)
Vapour Density: 3.4 (air=1) (at boiling point) (8)
Vapour Pressure: 0.004 kPa (0.03 mm Hg) (100%); 0.29 kPa (2.18 mm Hg) (85%); 0.75 kPa (5.63 mm Hg) (75%) at 20 deg C (10)
Saturation Vapour Concentration: 40 ppm (100%); 2870 ppm (85%); 7409 ppm (75%) at 20 deg C (calculated)
Evaporation Rate: Negligible
Critical Temperature: Not available


Normally stable. Orthophosphoric acid gradually changes to pyrophosphoric acid at about 200 deg C and forms metaphosphoric acid above 300 deg C.(11)

Hazardous Polymerization:
Will not occur

Incompatibility - Materials to Avoid:

NOTE: Chemical reactions that could result in a hazardous situation (e.g. generation of flammable or toxic chemicals, fire or detonation) are listed here. Many of these reactions can be done safely if specific control measures (e.g. cooling of the reaction) are in place. Although not intended to be complete, an overview of important reactions involving common chemicals is provided to assist in the development of safe work practices.

STRONG CAUSTICS (e.g. potassium hydroxide) - react violently, causing spattering and considerable release of heat.(9,16)
STRONG OXIDIZING AGENTS, REDUCING AGENTS or ORGANIC PEROXIDES- potentially dangerous reactions can occur.(14)
METALS - forms flammable and potentially explosive hydrogen gas.(9,13,14)
FLUORIDES, HALOGENATED ORGANICS, CYANIDES, SULFIDES, MERCAPTANS, NITRIDES, METAL PHOSPHIDES, ACETYLIDES, SILICIDES and CARBIDES - form toxic, corrosive and/or flammable gases such as hydrogen fluoride, hydrogen cyanide, hydrogen sulfide, ammonia, phosphine and acetylene.(11,14)
NITROMETHANE - addition of phosphoric acid to nitromethane makes nitromethane susceptible to initiation.(17)
SODIUM TETRAHYDROBORATE (sodium borohydride) - reaction with anhydrous acid is very exothermic (produces a great amount of heat) and may be dangerously violent with rapid mixing.(17)

Hazardous Decomposition Products:

Conditions to Avoid:

Corrosivity to Metals:
Very corrosive to ordinary ferrous metals and alloys, particularly when hot.(9) Not corrosive to stainless steel grades 302, 304, 316, 20-25-4.5 at room temperature, but may be corrosive when heated.(14,18)

Stability and Reactivity Comments:
May attack some plastics, rubber and coatings. May also attack porcelain, and graniteware when hot and earthenware and glass above 200 deg C.(9,11,12)


LC50 (mouse): 25.5 mg/m3 (concentration and duration of exposure not specified) (4, unconfirmed)

LD50 (oral, rat): 3500 mg/kg (85% water solution); 4200 mg/kg (80% water solution); 4400 mg/kg (75% water solution) (5)
LD50 (oral, mouse): 1250 mg/kg (4, unconfirmed)

LD50 (dermal, rabbit): greater than 1260 mg/kg (85% water solution) (5)

Eye Irritation:

Application of 0.1 mL of 75-85% phosphoric acid produced corrosive injury in rabbits.(5) In another study, application of a 17% solution produced mild irritation in rabbits (mean scores of 2.04 (redness), 0.61 (edema), 0.44 (corneal opacity) and 16% (corneal swelling)).(6)

Skin Irritation:

Application of 0.5 mL of 75-85% phosphoric acid for 24 hours, under semi-occlusive cover, produced corrosion in rabbits. Application of 0.5 mL of 85% phosphoric acid for 4 hours, under semi-occlusive cover, was also corrosive to rabbits, while the 75 or 80% solutions were not corrosive.(5)

Effects of Short-Term (Acute) Exposure:

Skin Contact:
Application of 631-7940 mg/kg of 75-85% water solutions of phosphoric acid to the intact skin of rabbits, under semi-occlusive cover, for 24 hours produced reduced appetite and activity, increasing weakness, collapse and death.(5)


Selected Bibliography:
(1) Boutoux, M., et al. Reactive airways dysfunction syndrome apres exposition aux vapeurs d'acide phosphorique. Archives des Maladies Professionnelles. Vol. 56, no. 1 (1995). p. 45-47
(2) Hawkins, D.B., et al. Caustic ingestion: controversies in management: a review of 214 cases. The Laryngoscope. Vol. 90 (1980). p. 98-109
(3) Dutton, C.B., et al. Lung function in workers refining phosphorus rock to obtain elementary phosphorus. Journal of Occupational Medicine. Vol. 35, no. 10 (Oct. 1993). p. 1028-1033
(4) Sigova, N.V. Toxicological characteristics of phosphoric acid and some of its chromium salts used as binding agents in the production of refractory materials. Gigiena Truda i Professional'naya Patologiya v Tsvetnoi i Chernoi Metallurgii. (1983). p. 65-69 (English translation: HSE Translation No. 14355A)
(5) Randall, D.J., et al. Acute toxicological evaluation of various concentrations of phosphoric acid. Journal of the American College of Toxicology. Part B. Acute Toxicity Data. Vol. 1 (1990). p. 69-70
(6) Jacobs, G.A., et al. An objective method for the evaluation of eye irritation in vivo. Food Chemistry and Toxicology. Vol. 27, no. 4 (1989). p. 255-258
(7) Al-Ani, F.Y., et al. Absence of mutagenic activity of acidity regulators in the Ames Salmonella/microsome test. Mutation Research. Vol. 206, no. 4 (1988). p. 467-470
(8) Von Burg, R. Toxicology Update: phosphoric acid/phosphates. Journal of Applied Toxicology. Vol. 12, no. 4 (1992). p. 301-303
(9) Emergency action guide for phosphoric acid. Association of American Railroads, Jan. 1988
(10) Gard, D.R. Phosphoric acids and phosphates. In: Kirk-Othmer encyclopedia of chemical technology. 4th ed. Vol. 18. John Wiley & Sons, 1996. p. 669-685
(11) HSDB database record for orthophosphoric acid. Date of last update: 9508.
(12) Chemical safety sheets: working safely with hazardous chemicals. Kluwer Academic Publishers, 1991. p. 704-705
(13) Fire protection guide to hazardous materials. 13th ed. Edited by A.B. Spencer, et al. National Fire Protection Association, 2002. NFPA 49
(14) Environmental and technical information for problem spills: phosphoric acid. Environment Canada, 1985
(15) Schrodter, K, et al. Phosphoric acid and phosphates. Ullmann's encyclopedia of industrial chemistry. 5th completely revised ed. Vol. A 19. VCH Verlagsgesellschaft, 1991. p. 465-478
(16) NIOSH pocket guide to chemical hazards. National Institute for Occupational Safety and Health, June 1994. p. 254-255
(17) Bretherick, L. Bretherick's handbook of reactive chemical hazards. 5th ed. Vol. 1. p. 70, 184, 1561-1562
(18) Corrosion data survey. Metals section. 6th ed. National Association of Corrosion Engineers, 1985. p. 96-97
(19) European Economic Community. Commission Directive 93/72/EEC. Sept. 1, 1993
(20) Forsberg, K., et al. Quick selection guide to chemical protective clothing. 4th ed. Van Nostrand Reinhold, 2002
(21) Occupational Safety and Health Administration (OSHA). Acid Mists in Workplace Atmospheres. In: OSHA Analytical Methods Manual. Revision Date: Oct. 31, 2001. Available at:>
(22) Occupational Safety and Health Administration (OSHA). Phosphoric Acid in Workplace Atmospheres. In: OSHA Analytical Methods Manual. Revision Date: Oct. 31, 2001. Available at:>
(23) National Institute for Occupational Safety and Health (NIOSH). Acids, Inorganic. In: NIOSH Manual of Analytical Methods (NMAM(R)). 4th ed. Edited by M.E. Cassinelli, et al. DHHS (NIOSH) Publication 94-113. Aug. 1994. Available at: <>

Information on chemicals reviewed in the CHEMINFO database is drawn from a number of publicly available sources. A list of general references used to compile CHEMINFO records is available in the database Help.

Review/Preparation Date: 1996-06-10

Revision Indicators:
Stability and reactivity comments 1996-12-01
Handling 1996-12-01
Emergency overview 1996-12-01
US transport 1998-03-01
Resistance of materials 1998-04-01
Bibliography 1998-04-01
TDG 2002-05-29
US transport 2002-12-10
Bibliography 2003-04-16
PEL transitional comments 2003-12-04
Resistance of materials for PPE 2004-04-03
Bibliography 2004-04-03
Bibliography 2005-03-05
Passive Sampling Devices 2005-03-05
Sampling/analysis 2005-03-05

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