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CHEMINFO Record Number: 292
CCOHS Chemical Name: Nitric acid

Aqua fortis
Azotic acid
Hydrogen nitrate
Nitryl hydroxide
Engraver's acid

Chemical Name French: Acide nitrique
Chemical Name Spanish: Acido nítrico
CAS Registry Number: 7697-37-2
UN/NA Number(s): 2031
RTECS Number(s): QU5775000
EU EINECS/ELINCS Number: 231-714-2
Chemical Family: Mineral acid / inorganic acid / hydrogen nitrate
Molecular Formula: H-N-O3
Structural Formula: H-O-N(O)=O


Appearance and Odour:
Clear, colourless or yellowish liquid with an acrid, suffocating odour.(1) Hygroscopic (absorbs moisture from the air).(1,13)

Odour Threshold:
0.29-0.98 ppm (cited as 0.75 to 2.5 mg/m3) (detection) (2)

Warning Properties:
NOT RELIABLE - Odour threshold about the same magnitude as TLV. Irritation has been reported at 60.6 ppm (cited as 155 mg/m3) (30 times greater than TLV).(2)

"Concentrated" nitric acid is commercially available at concentrations ranging from 50-70% (wt/wt), with limited amounts (0.5%) of chlorides, sulfate, arsenic, heavy metals and iron. Very low levels (below 0.1%) of nitrogen oxides (e.g. nitrous acid) may also be present. This CHEMINFO review presents hazard information and control measures for concentrated nitric acid. It does not deal with the hazards of and control measures for concentrated "fuming" nitric acid. "Fuming" acids are usually greater than 85% nitric acid, and contain significant amounts of nitrogen oxides.

Uses and Occurrences:
The largest use of nitric acid is for the manufacture of ammonium nitrate (used for fertilizers, explosives and other chemical uses), followed by the manufacture of cyclohexanone, dinitrotoluene, and nitrobenzene. It is also used as a nitrating agent in the preparation of explosives; in the production of metal nitrates, and aliphatic and aromatic nitrates; nitrocellulose; nitrochlorobenzene; and rocket propellants (in rocket fuel production); for metal treatments; and as a chemical in metallurgy (e.g. as an etching and pickling agent for stainless steels); used in the printing industry for photo-engraving; for ore flotation; and reprocessing spent nuclear fuel.(1,3,6)


Clear, colourless or yellowish liquid with an acrid, suffocating odour. Hygroscopic. Will not burn. During a fire, nitric acid decomposes with the release of corrosive nitrogen oxide gases. Closed containers may develop pressure on prolonged exposure to heat. STRONG OXIDIZER. Contact with combustible and easily oxidizable materials may result in fire and/or explosion. Highly reactive. May react violently or explosively and/or ignite spontaneously with many organic and inorganic chemicals. Releases extremely flammable hydrogen gas on contact with many metals, particularly in powered form. Generates heat when mixed with water. Nitric acid poses a very serious inhalation hazard. Symptoms of exposure include dryness of the nose and throat, cough, chest pain, shortness of breath and difficulty breathing. Causes lung injury-effects may be delayed. CORROSIVE to the eyes, skin and respiratory tract. Causes severe burns. May cause permanent eye injury or blindness and permanent scarring.


Effects of Short-Term (Acute) Exposure

Nitric acid readily forms a high vapour concentration at room temperature. It is very corrosive and can release other corrosive and toxic gases upon contact with air (20), organic materials or metals, thus posing a very serious inhalation hazard. Symptoms of exposure include dryness of the nose and throat, cough, chest pain, shortness of breath and difficulty breathing. A severe exposure can result in a potentially fatal accumulation of fluid in the lungs (pulmonary edema). Symptoms of pulmonary edema (chest pain and shortness of breath) can be delayed for up to 24 or 48 hours after exposure.
The presence of nitrogen oxide gases, like nitrogen dioxide, contributes significantly to the toxic effects observed following nitric acid exposure. However, the strongly corrosive nitric acid is expected to be a severe respiratory irritant on its own.(21) For more information on nitrogen dioxide, refer to the CHEMINFO review of nitrogen dioxide.
A case report describes a 58-year-old male who was accidentally exposed to nitric acid fumes for about 10 minutes after dipping the wrong metal into a vat of nitric acid (concentration not specified). He developed pulmonary edema, cardiac failure and bronchopneumonia, which were controlled with medical treatment. However, he died from pulmonary fibrosis 18 days later.(22)
Another case report describes 3 young men, working in a pulp mill, who died from pulmonary edema within 24 hours following exposure to an airborne chemical mixture released from the explosion of a tank that contained 68% nitric acid.(20)
A historical case report describes a 45-year-old male exposed to vapours from spilled nitric acid for about 20 minutes. He died 25 hours later with severe damage to the respiratory and digestive systems.(23)

Skin Contact:
Nitric acid is corrosive. Corrosive materials are capable of producing severe burns, blisters, ulcers and permanent scarring, depending on the concentration of the solution and the duration of contact. Concentrated solutions produce burns, lower concentrations cause a change in skin colour from yellow to brown, and dilute solutions cause mild irritation of the skin and can harden the skin.(21)

Eye Contact:
Nitric acid is corrosive. Corrosive materials are capable of producing severe eye burns, and permanent injury, including blindness, depending on the concentration of the solutions and duration of contact. There is one report of severe corrosive damage to the eyes with blindness in 4 newborn children from the mistaken application of nitric acid in place of silver nitrate.(24)

Nitric acid is corrosive and can cause burns to the lips, tongue, throat and stomach, abdominal pain, nausea, vomiting, diarrhea and death if ingested. Because of immediate pain when taken into the mouth, strong mineral acids are not often swallowed.(25) In non-occupational incidents of accidental and suicidal ingestion, nitric acid has been reported to cause burns to the skin, mouth, esophagus, and digestive system and in some cases death.(21) The lowest located lethal dose in humans is 430 mg/kg.(19, unconfirmed) No further details are available for evaluation. Ingestion is not a typical route of occupational exposure.

Effects of Long-Term (Chronic) Exposure

Long-term exposure to corrosive materials, like nitric acid, can cause skin and respiratory irritation, with the possible development of lung injury (e.g. chronic bronchitis).(21) Exposure to nitric acid vapours, mists or aerosols has been shown to cause dental erosion.

Lungs/Respiratory System:
Long-term exposure to corrosive materials, like nitric acid, can cause chronic respiratory irritation, which may result in conditions like chronic bronchitis or airways hyperreactivity, although there is little specific information available for nitric acid.
No conclusions can be drawn from a limited study of 142 workers from 2 plants, where 113 workers were exposed to nitric acid and 29 were controls. The actual concentrations of nitric acid and other nitrogen oxides were not reported. In one plant, chronic respiratory symptoms (laboured breathing, dry cough, sputum, frequent colds and throat irritation) were higher, but not significantly higher, than the controls. In the same plant, there was a significant decrease in measurements of lung function in exposed workers compared to controls.(26) This study is limited by factors such as the small number of controls, a high incidence of "unrelated symptoms" in the controls, and the lack of exposure information.

Repeated skin contact with low concentrations of acid solutions, mists or vapour can cause redness, swelling and pain (dermatitis).

DENTAL EROSION: Repeated exposure to nitric acid vapours, mists or aerosols is believed to cause dental erosion. The airborne chemical is thought to deposit on teeth and react with tooth enamel resulting in decalcification.(21,27)
In one study, 32 workers exposed to an unspecified concentration of nitric acid were studied over a period of 2 years and compared to 293 controls. Of the exposed workers, a small number (3/32 or 9%) had active dental erosion, compared to 0/293 of the unexposed workers.(28) Most other studies that have shown dental erosion involved workers exposed to mixtures of sulfuric and nitric acid.(21)


There is insufficient information available to evaluate the potential of nitric acid to cause cancer. A case-control study of laryngeal cancer suggested that Polish workers regularly exposed to vapours of nitric acid, sulfuric acid and hydrochloric acid had significantly higher rates of laryngeal cancer than controls.(28) This study was evaluated by the International Agency for Research on Cancer and they determined that no conclusions can be drawn from this study due to the inadequate description of the study methodology.(30) There is no animal information available.

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

IARC has concluded that occupational exposure to strong-inorganic-acid mists containing sulfuric acid is carcinogenic to humans (Group 1).(30)

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 information available. The only animal study located is not available in English and cannot be evaluated.

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

There is no human or animal information available.

Toxicologically Synergistic Materials:
There is no information available.

Potential for Accumulation:
Nitric acid is not expected to accumulate.

Health Comments:
There is evidence that some people with asthma may be more sensitive to acid aerosols than healthy individuals.(31) Nitric acid is a prevalent air pollutant and has the potential to cause adverse respiratory effects through acidification and oxidation reactions.


Take proper precautions to ensure your own safety before attempting rescue (e.g. wear appropriate protective equipment, use the "buddy" system). Remove source of contamination or move victim to fresh air. If breathing is difficult, oxygen may be beneficial if administered by a trained personnel, preferably on a doctor's advice. Do not allow victim to move about unnecessarily. Symptoms of pulmonary edema can be delayed up to 48 hours after exposure. Immediately transport victim to an emergency care facility.

Skin Contact:
Avoid direct contact with this chemical. Wear chemical protective clothing, if necessary. Immediately remove contaminated clothing, shoes, and leather goods (e.g. watchbands, belts). As quickly as possible, flush contaminated area with lukewarm, gently running water for at least 20-30 minutes, by the clock. DO NOT INTERRUPT FLUSHING. If necessary, keep emergency vehicle waiting. Immediately transport victim to an emergency care facility. Discard contaminated clothing, shoes and leather goods. Keep contaminated clothing under water in a closed container until it can be safely discarded.

Eye Contact:
Avoid direct contact. 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, holding the eyelid(s) open. Neutral saline 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 unaffected 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. If milk is available, it may be administered after the water has been given. If vomiting occur 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.
Some recommendations in the above sections may be considered medical acts in some jurisdictions. These recommendations should be reviewed with a doctor and appropriate delegation of authority obtained, as required.
All first aid procedures should be periodically reviewed by a doctor familiar with the material and its conditions of use in the workplace.


Flash Point:
Not combustible (does 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:
Probably not sensitive. Normally stable.

Sensitivity to Static Charge:
Nitric acid will not accumulate static charge, since it has a very high electrical conductivity.(7) Since it does not burn, nitric acid will not be ignited by a static discharge.

Electrical Conductivity:
Not available for nitric acid concentrations of 70% or less; 3.77 x 10(12) pS/m at 0 deg C (100% nitric acid).(7)

Minimum Ignition Energy:
Not applicable

Combustion and Thermal Decomposition Products:
Liquid decomposes to a limited extent when heated, producing corrosive nitrogen oxides.(3,6,8)

Fire Hazard Summary:
Nitric acid does not burn. However, nitric acid is a strong OXIDIZING AGENT and is a serious fire and explosion hazard. Nitric acid can cause combustible materials such as wood, paper, cotton, wool, cloth, oils and grease to ignite spontaneously and will support, accelerate and intensify the burning of combustible materials in a fire. Can react with many metals, particularly in powdered form, to form extremely flammable hydrogen gas. Generates heat when mixed with water. During a fire, nitric acid decomposes with the release of corrosive nitrogen oxide gases. Explosive decomposition may occur under fire conditions and closed containers may rupture violently due to rapid decomposition, if exposed to fire or excessive heat for a sufficient period of time.

Extinguishing Media:
Nitric acid does not burn. Extinguish fire using extinguishing agent suitable for the surrounding fire and not contraindicated for use with nitric acid. Nitric acid is an oxidizer. Therefore, flooding quantities of water spray or fog should be used to fight fires involving nitric acid.(8)

Extinguishing Media to be Avoided:
DO NOT use dry chemical powders containing sodium bicarbonate, potassium bicarbonate, sodium carbonate, calcium carbonate, ammonium phosphate or ammonium sulfate. Nitric acid can react violently with these extinguishing agents.

Fire Fighting Instructions:
Extreme caution is required in a fire situation. Evacuate area and fight fire from a protected, explosion-resistant location or maximum possible distance. Approach fire from upwind to avoid hazardous decomposition products. Wear full chemical protective suit if exposure is possible. See Protection of Firefighters. Remove all flammable and combustible materials from the vicinity, especially oil and grease.
If possible, isolate materials not involved in the fire, if this can be done without risk, and protect personnel. If nitric acid is not involved in the fire, move nitric acid containers from the fire area only if they have not been exposed to heat. Use extreme caution since explosive decomposition can occur under fire conditions and heat may rupture containers. Otherwise, apply water from as far a distance as possible, in flooding quantities as a spray or fog to keep fire-exposed containers or equipment cool and absorb heat, until well after the fire is out. No part of a container should be subjected to a temperature higher than 49 deg C (120 deg F).(32) Take care that water does not come into contact with the acid, since even small quantities of water added to concentrated nitric acid can generate heat and cause spattering.
Stay away from ends of tanks, but realize that flying material from ruptured tanks may travel in any direction. Withdraw immediately in case of rising sound from venting safety device or any discolouration of tanks due to fire. In an advanced or massive fire, the area should be evacuated. Use unmanned hoseholders or monitor nozzles.
Containers should not be approached directly after they have been involved in a fire or heated by exposure, until they have been completely cooled down. Clean-up or salvage operations should not be attempted until the nitric acid is cooled. After the fire has been extinguished, corrosive and toxic atmospheres may linger. Before entering such an area, especially confined areas, check the atmosphere with an appropriate monitoring device while wearing a full chemical protective suit.

Protection of Fire Fighters:
Nitric acid and it's decomposition products are corrosive and toxic. 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 protective clothing (e.g. chemical splash suit and positive pressure self-contained breathing apparatus (NIOSH approved or equivalent) may be necessary.


NFPA - Health: 4 - Very short exposure could cause death or major residual injury. (Nitric acid greater than 40%); 3 - Short exposure could cause serious temporary or residual injury. (Nitric acid less than or equal to 40%)
NFPA - Flammability: 0 - Will not burn under typical fire conditions. (Nitric acid greater than 40%; Nitric acid less than or equal to 40%)
NFPA - Instability: 0 - Normally stable, even under fire conditions, and not reactive with water.(Nitric acid greater than 40% or Nitric acid less than or equal to 40%)
NFPA - Specific Hazards: OXIDIZING MATERIAL (Nitric acid greater than 40%)


Molecular Weight: 63.02

Conversion Factor:
1 ppm = 2.57 mg/m3; 1 mg/m3 = 0.39 ppm at 25 deg C (calculated)

Physical State: Liquid
Melting Point: -41 deg C (-42 deg F) (70% nitric acid) (6); -20 deg C (-4 deg F) (50%) (6)
Boiling Point: 120.5 deg C (248.9 deg F) (68%) (33); 114.7-116.4 deg C (238.5-241.5 deg F) (50%) (6,34)
Relative Density (Specific Gravity): 1.41 (68%) (33); 1.31 (50%) (14) (water = 1)
Solubility in Water: Soluble in all proportions.(3,33)
Solubility in Other Liquids: No information available. Reacts with many organic solvents (e.g. alcohols, ketones, ethers and esters).
Coefficient of Oil/Water Distribution (Partition Coefficient): Log P(oct) = 0.21 (estimated) (35)
pH Value: 1.0 (0.1 M solution) (13)
Acidity: Strong acid
Dissociation Constant: pKa = -1.38 (36)
Viscosity-Dynamic: Not available for nitric acid concentrations of 70% and less.
Surface Tension: Not available for nitric acid concentrations of 70% and less.
Vapour Density: 2.17 (air = 1) (calculated)
Vapour Pressure: PARTIAL PRESSURE: 70% nitric acid: 0.37-0.4 kPa (2.78-3 mm Hg) at 20 deg C (3,14); 0.547 kPa (4.1 mm Hg) at 25 deg C (14) 50% nitric acid : 0.036-0.04 kPa (0.27-0.3 mm Hg) at 20 deg C (3,14); 0.052 kPa (0.39 mm Hg) at 25 deg C (14)
Saturation Vapour Concentration: 70% nitric acid: 3700-3900 ppm (0.37-0.39%) at 20 deg C; 5400 ppm (0.54%) at 25 deg C (calculated) 50% nitric acid: 400 ppm (0.04%) at 20 deg C; 500 ppm (0.05%) (50%) at 25 deg C (calculated)
Evaporation Rate: Information not available
Henry's Law Constant: 2.48 x 10(3) Pa.m3/mol (cited as 2.45 x 10(-2) (atm.m3/mol)at 25 deg C (36); log H = 0 (dimensionless constant; calculated)


Normally stable. Nitric acid has a tendency to slowly decompose at room temperature to form nitrogen oxides, which may colour the acid yellow or red. The decomposition is accelerated by exposure to light and increases in temperature.(3,6)

Oxidizing Properties:
The NFPA lists nitric acid (40% or less) as a Class 1 oxidizer and nitric acid (more than 40% but less than 80%) as a Class 2 oxidizer. A Class 1 oxidizer meets the definition of an oxidizer (any material that readily yields oxygen or other oxidizing gas, or that readily reacts to promote or initiate combustion of combustible materials) and does not moderately increase the burning rate of combustible materials with which it comes into contact. A Class 2 oxidizer will cause a moderate increase in the burning rate of combustible materials with which it comes into contact.(8,32)

Hazardous Polymerization:
Does 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.

Nitric acid is a strong acid and a strong oxidizing agent and is very reactive. Nitric acid is frequently involved in reactive incidents.(17) References 8, 13, 17 and 37 review hazardous reactions and incompatible materials.

MOST METALS particularly POWDERED METALS (e.g. antimony, bismuth, germanium, manganese or titanium), ALKALI METALS (e.g. lithium or sodium) or ALKALINE EARTH METALS (e.g. magnesium or calcium) - may react violently or explosively, and/or cause fire, with generation of extremely flammable hydrogen gas.(8,13,17,37)
ORGANIC CHEMICALS (e.g., alcohols, acids, anhydrides, aldehydes, ketones, amines, ethers, hydrocarbons, alkanethiols, nitriles, nitroalkanes and nitroaromatics) - may react violently or explosively, and/or ignite spontaneously.(8,17,37)
NON-METALS (e.g. arsenic, boron, finely divided carbon, phosphorus or silicon), NON-METAL HYDRIDES (e.g. arsine, phosphine, stibine or tetraborane) or REDUCING AGENTS (e.g. potassium phosphinate) - may react violently or explosively and ignite.(13,17,37)
CROTONALDEHYDE, HYDRAZINE, DIMETHYLHYDRAZINE, DIVINYL ETHER, PYROCATECHOL - ignite spontaneously (hypergolic) on contact with concentrated nitric acid, the ignition delay being 1 millisecond (ms).(17)
SULFIDES (e.g. sodium or potassium sulfide) - toxic and flammable hydrogen sulfide gas and toxic sulfur dioxide gas may be generated.(13)
CARBIDES (e.g. cesium carbide), FLUORINE, PHOSPHORUS HALIDES (e.g. phosphorus trichloride) or OTHER PHOSPHORUS COMPOUNDS (e.g. cadmium phosphide) - may ignite and/or explode.(8,13,17,37)
METAL CYANIDES (e.g. sodium cyanide, potassium cyanide or calcium cyanide) - mixture produces a violent reaction, with formation of very toxic and flammable hydrogen cyanide.(8,13,17)
SULFUR HALIDES (e.g. sulfur dichloride or disulfur dibromide) - interaction is violent, with generation of the corresponding hydrogen halide.(17)

Hazardous Decomposition Products:
Nitrogen oxides

Conditions to Avoid:
Air, light, high temperatures

Corrosivity to Metals:
Nitric acid (5-70%) is corrosive (corrosion rate greater than 1.25 mm/year) to most metals at 21 deg C (70 deg F), including carbon steel (e.g. types 1010, 1020, 1075 and 1095), type 3003 aluminum, cast iron (e.g. gray, ductile and high nickel cast iron), nickel, nickel-base alloys (e.g. Monel and Hastelloy B and D), copper, copper-nickel, bronze (unspecified), aluminum bronze, silicon bronze, brass (unspecified), admiralty brass, naval brass and lead.(38,39) It attacks (corrosion rate less than or equal to 0.5 mm/year to grater than or equal to 1.27 mm/year) some 400 series stainless steels at 21 deg C.(38) Stainless steels with high chromium content (most 300 series) exhibit excellent or good resistance to nitric acid. concentrations ranging from 0-65% up to the boiling point. Types 304, 304L, R12S, 2RE10 (high chromium and nickel content) and 7-Mo duplex stainless steel are particularly recommended for use with nitric acid. High-silicon cast iron (Duriron) and high-chromium cast iron, higher chromium nickel alloys (e.g. G-30 and 690), nickel-base alloys (e.g. Hastelloy C and Incoloy 825), tantalum, titanium, zirconium, gold and platinum-type metals also have excellent resistance to nitric acid.(38,40,41,42) Aluminum alloys (types 1100 and 3003) can only be used for very high concentrations of nitric acid (80-100%). (40,41)

Corrosivity to Non-Metals:
Nitric acid (5-100%) at 21 deg C attacks plastics, such as acrylonitrile-butadiene-styrene (ABS), nylon, styrene-acrylonitrile, polystyrene and polyurethane; and elastomers, such as nitrile Buna N (NBR), natural rubber, isoprene, neoprene, chloroprene, polyester, styrene butadiene (SBR), polyurethane, chlorinated polyethylene, ethylene-propylene, ethylene-propylene terpolymer and low density polyethylene.(39,43,44) Nitric acid (5-100%) does not attack plastics, such as Teflon, and other fluorocarbons; and elastomers such as Viton and other fluorocarbons (e.g. Kalrez and Chemraz (up to 50%)). Nitric acid (concentrations up to 50%) does not attack plastics, e.g. polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), polypropylene, thermoset polyester (Bisphenol A-fumarate and Isophthalic acid), high density polyethylene and ultra high molecular weight polyethylene and elastomers e.g. butyl rubber.(39,41,43,44)

Stability and Reactivity Comments:
Heat is generated when concentrated nitric acid is mixed with water.(13) The acid must be added slowly to water with stirring to avoid possible splattering.


No standard acute lethality values were located for nitric acid.

Skin Irritation:

Nitric acid is corrosive to the skin, based on pH.

Application of 1 mL of 10 or 20% nitric acid to rabbit skin for 1 hour caused brown pigmentation, thinning, drying and cracking of the skin.(4)

Effects of Short-Term (Acute) Exposure:

In a non-standard test, anesthetized dogs (4 treated/3 control) were exposed by intubation to 1% nitric acid as a coarse spray (5 or 8 mL) once/week and a fine spray (2 mL/min) twice/week for 4 weeks (2 hrs/d). This treatment caused inflammation, slight swelling and tissue damage in the respiratory tract.(15) In another study, anesthetized dogs (7 treated/3 control) were exposed in the same way for the same length of time. During exposure, the dogs developed a cough that persisted for 1 month after exposure stopped. The treatment did not affect body weight, or breathing when at rest. However, most animals had rapid respiration with moderate exercise. There was evidence of chronic airway inflammation and swelling, with permanent damage to the respiratory tract.(5) These studies are limited because of small animal numbers, unknown exposure concentrations and the route of exposure is not typical of occupational settings. Rats exposed once to 25 ppm (cited as 63 mg/m3) for an unspecified duration showed no apparent effects.(9, unconfirmed) There are no further details available for evaluation.

Effects of Long-Term (Chronic) Exposure:

Male rats exposed (nose-only) to 0.0195 ppm (cited as 50 microg/m3) nitric acid vapour (produced from a 6N solution of nitric acid) for 40 weeks (4 hr/d, 3 d/wk) showed no effects on polyamine metabolism, indicating that an inflammatory response had not been induced.(10) In another study, male rats exposed in the same way to 0.0195 ppm (cited as 50 microg/m3) nitric acid vapour did not show any changes in the rates of particle clearance from the respiratory tract.(16) In a study, which is not available in English, continuous exposure of rats to 0.42 ppm (cited as 1.07 mg/m3) for 12 weeks, caused muscle contraction, and changes in urine and enzyme levels.(19, unconfirmed) There are no other details available for evaluation.

Teratogenicity, Embryotoxicity and/or Fetotoxicity:
No conclusions can be drawn from a single study, which is not available in English, that reported fetotoxicity in the offspring of rats following oral exposure.(19, unconfirmed) There are insufficient details available for evaluation.


Selected Bibliography:
(1) Lewis, Sr., R.J., ed. Nitric acid. Hawley's condensed chemical dictionary. [CD-ROM]. 14th ed. John Wiley and Sons, Inc., 2002
(2) Ruth, J.R. Odor thresholds and irritation levels of several chemical substances : a review. American Industrial Hygiene Association Journal. Vol. 47 (Mar. 1986). p. A-142, A-149
(3) Clarke, S.I., et al. Nitric acid. In: Kirk-Othmer encyclopedia of chemical technology. 4th ed. Vol. 17. John Wiley and Sons, 1996. p. 80-107. Also available at: <> (Subscription required)
(4) The protecting influence of specially compounded salves upon skin exposed to industrial chemical hazards. Milburn Co., 1975. {NIOSHTIC Control No. 00043214}
(5) Fujita, M., et al. Canine model of chronic bronchial injury. Lung mechanics and pathologic changes. American Review of Respiratory Diseases. Vol. 137, no. 2 (1988). p. 429-434
(6) Thiemann, M., et al. Nitric acid, nitrous acid, and nitrogen oxides. In: Ullmann's encyclopedia of industrial chemistry. 7th ed. John Wiley and Sons, 2002. Also available at: <> (Subscription required)
(7) Stern, S. A. et al. The physicochemical properties of pure nitric acid. Chemical Reviews. Vol. 60, no. 2 (1960). p. 186-207
(8) Fire protection guide to hazardous materials. 13th ed. Edited by A.B. Spencer, et al. National Fire Protection Association, 2002. NFPA 49; NFPA 491
(9) Diggle, W.M., et al. The toxicity of nitrogen pentoxide. British Journal of Industrial Medicine. Vol. 11 (1954). p. 140-144
(10) Sindhu, R.K., et al. Chronic exposure to ozone and nitric acid vapor results in increased levels of rat pulmonary putrescine. Archives of Toxicology. Vol. 72, no. 7 (1998). p. 445-449
(11) Nitric acid. In: NIOSH pocket guide to chemical hazards. National Institute of Occupational Safety and Health, June 1997. p. 224-225
(12) Forsberg, K., et al. Quick selection guide to chemical protective clothing. 4th ed. Van Nostrand Reinhold, 2002
(13) Environmental and technical information for problems spills (EnviroTIPS): nitric acid. Environment Canada, 1985
(14) Perry, R.H., et al. eds. Perry's chemical engineers' handbook. 7th ed. McGraw Hill, 1997. p. 2-20, 2-84, 2-102 to 2-103
(15) Peters, S.G., et al. A canine model of bronchial injury induced by nitric acid. American Review of Respiratory Disease. Vol. 133, no. 6 (1986). p. 1049-1054
(16) Mannix, R.C., et al. Effects of repeated exposure to nitric acid vapor and ozone on respiratory tract clearance in the rat. Inhalation Toxicology. Vol. 8 (1996). p. 595-605
(17) Urben, P.G., ed. Bretherick's reactive chemical hazards database. [CD-ROM]. 6th ed. Version 3.0. Butterworth-Heinemann Ltd., 1999
(18) European Economic Community. Commission Directive 93/72/EEC. Sept. 1, 1993
(19) National Institute for Occupational Safety and Health (NIOSH). Nitric acid. Last updated: 2000-07. In: Registry of Toxic Effects of Chemical Substances (RTECS(R)). [CD-ROM]. Canadian Centre for Occupational Health and Safety (CCOHS). Also available at: <>
(20) Hajela, R., et al. Fatal pulmonary edema due to nitric acid fume inhalation in three pulp-mill workers. Chest. Vol. 97, no. 2 (Feb. 1990). p. 487-491
(21) National Institute for Occupational Safety and Health (NIOSH). Criteria for a recommended standard: occupational exposure to nitric acid. US Department of Health Education and Welfare, 1976
(22) Treiger, P., et al. Nitric acid fume pneumonia. Industrial Medicine. Vol. 16, no. 8 (Aug. 1947). p. 395-397
(23) Desgranges, J.B. Observations and comments on a sudden death caused by nitrous gas. {Translation}. Journal de Medicine, Chirurgie, Pharmacie, etc. Vol. 8 (1804). p. 487-505 {NIOSHTIC Control No. 00053170}
(24) Ask, F. Four cases of severe corrosive damage to the eyes through accidental interchange of crede-solution and nitric acid. {Translation}. Svenska Lakartidningen. Vol. 22, no. 15 (1925). p. 449-453 {NIOSHTIC Control No. 00053159}
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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: 2004-10-19

Revision Indicators:
TDG 2005-10-18
US transport 2005-10-18
Bibliography 2006-01-02

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