Nitric Acid


Nitric acid, also known as aqua fortis and spirit of niter, is a highly corrosive strong mineral acid with the molecular formula HNO3. The pure compound is colourless, but older samples tend to acquire a yellow cast due to decomposition into oxides of nitrogen and water. Most commercially available nitric acid has a concentration of 68%. When the solution contains more than 86% HNO3, it is referred to as fuming nitric acid. Depending on the amount of nitrogen dioxide present, fuming nitric acid is further characterised as white fuming nitric acid or red fuming nitric acid, at concentrations above 95%. Nitric acid is the primary reagent used for nitration – the addition of a nitro group, typically to an organic molecule. Nitric acid is also a strong oxidising agent. [1]

Uses [2]

Nitric acid is used in a wide variety of chemical processes where cleaning, oxidising or etching is required, including making synthetic fibres, dying, electrical circuit board making, electroplating, explosives, laboratory chemicals, metal cleaning and etching, semiconductors, pharmaceutical manufacture. It is used in the manufacture of fertilisers and other organic chemicals, in the printing industry for photoengraving, in jewellery manufacturing, and for wet chemical etching.

Routes of Exposure

  • Industry sources: Released from industries producing, using or handling nitric acid, for example chemical plants, metal, electronic, printing, glass, rubber and plastics plants and industries. Where ever very high temperature combustion takes place in the atmosphere in the presence of nitrogen, oxygen and water. May be present in small amounts in some wastewater from intensive farm factories and other facilities, which produce wastewater containing high level of nitrogen.
  • Diffuse sources: May be present in exhaust gases from motor vehicles, the exhaust of incinerators or other chemical plants, or where these are in contact with moisture in the air. Unlikely to persist in nature because it readily reacts with a wide variety of naturally occurring substances.
  • Natural sources: Rare in nature as a gas in the atmosphere, in groundwater around active volcanic regions, or drainage from areas where accumulated organic or animal wastes are present.
  • Transport sources: Exhaust chambers in motor vehicles.
  • Consumer products: Could be retained as small amounts in products where it has been used in the manufacturing or treatment process.

The major routes of exposure to nitric acid are:

  • inhalation,
  • ingestion,
  • skin and/or eye contact

Health Effects [4]

Acute Effects

  • Nitric acid is irritating and corrosive to all tissues with which it comes into contact. The severity of effects is dependent upon concentration and duration of exposure.
  • Acute inhalation of nitric acid vapour can lead to symptoms such as ocular and nasal irritation, sore throat, cough, chest tightness, headache, ataxia and confusion
  • In severe cases, pulmonary oedema may develop hours or days following exposure
  • Acute ingestion may cause burns to the oesophagus and stomach, which can include ulceration, haemorrhage and perforation. Abdominal pain, difficulty swallowing, nausea, salivation, vomiting, diarrhoea and haematemesis may also occur, and in some cases may be fatal
  • Dermal exposure may result in deep burns, blisters and permanent scarring
  • Ocular exposure may cause corneal burns, lacrimation, conjunctivitis, photophobia and, in severe cases, could lead to permanent blindness

Chronic Effects

  • Chronic inhalation exposure to nitric acid can cause respiratory irritation, leading to bronchitis and airways hyperreactivity and erosion of dental enamel.
  • Chronic ingestion is unlikely due to the adverse effect of acute ingestion
  • Dermal exposure to low concentrations of nitric acid can result in dermatitis
  • Nitric acid is not considered to be carcinogenic or mutagenic

Safety [5]

First Aid Measures

  • Eye Contact: Check for and remove any contact lenses. In case of contact, immediately flush eyes with plenty of water for at least 15 minutes. Cold water may be used. Get medical attention immediately.
  • Skin Contact: In case of contact, immediately flush skin with plenty of water for at least 15 minutes while removing contaminated clothing and shoes. Cover the irritated skin with an emollient. Cold water may be used. Wash clothing before reuse. Thoroughly clean shoes before reuse. Get medical attention immediately.
  • Serious Skin Contact: Wash with a disinfectant soap and cover the contaminated skin with an anti-bacterial cream. Seek immediate medical attention.
  • Inhalation: If inhaled, remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. Get medical attention immediately.
  • Serious Inhalation: Evacuate the victim to a safe area as soon as possible. Loosen tight clothing such as a collar, tie, belt or waistband. If breathing is difficult, administer oxygen. If the victim is not breathing, perform mouth-to-mouth resuscitation. WARNING: It may be hazardous to the person providing aid to give mouth-to-mouth resuscitation when the inhaled material is toxic, infectious or corrosive. Seek immediate medical attention.
  • Ingestion: Do NOT induce vomiting unless directed to do so by medical personnel. Never give anything by mouth to an unconscious person. If large quantities of this material are swallowed, call a physician immediately. Loosen tight clothing such as a collar, tie, belt or waistband.

Fire & Explosion Information

Flammability Information

Nitric acid is flammable in the presence of cellulose or other combustible materials. Phosphine, hydrogen sulphide, selenide all ignite when fuming nitric acid is dripped into gas. Phosphine ignites in concentrated nitric acid. Nickel tetraphosphide ignites with fuming nitric acid. Contact with metals may evolve flammable hydrogen gas. A jet of ammonia will ignite nitric acid vapour. Cellulose may be converted to the highly flammable nitrate ester on contact with the vapour of nitric acid as well as the liquid.

Explosion Information

Nitric acid reacts explosively with metallic powders, carbides, cyanides, sulphides, alkalis and turpentine. Can react explosively with many reducing agents. Arsine, phosphine, tetraborane all oxidised explosively in presence of nitric acid. Caesium and rubidium acetylides explode in contact with nitric acid. Explosive reaction with Nitric Acid + Nitrobenzene + water. Detonation with Nitric Acid + 4-Methylcyclohexane. The addition of warm fuming nitric acid to phosphine causes explosion. Addition of water to nitration mixture diluted with an equal volume of water can cause a low order explosion. Cyclopentadiene reacts explosively with fuming nitric acid. Mixtures of fuming nitric acid and acetonitrile are high explosives. (Nitric acid, fuming).

Exposure Controls & Personal Protection

Engineering Controls

Exhaust ventilation or other engineering controls should be provided to keep the airborne concentrations of vapours below their respective threshold limit value. Ensure that eyewash stations and safety showers are proximal to the workstation location.

Personal Protective Equipment

The following personal protective equipment is recommended when handling nitric acid:

  • Face shield;
  • Full suit;
  • Vapour respirator (be sure to use an approved/certified respirator or equivalent);
  • Gloves;
  • Boots

Personal Protective Equipment in Case of a Large Spill:

  • Splash goggles;
  • Full suit;
  • Vapour respirator;
  • Boots;
  • Gloves;
  • A self-contained breathing apparatus should be used to avoid inhalation of the product.
  • Suggested protective clothing might not be sufficient; consult a specialist BEFORE handling this product.


United States [3]

NIOSH: The National Institute for Occupational Safety & Health has established a Recommended Exposure Limit (REL) for nitric acid of TWA 2 ppm (5 mg/m3) and short-term concentrations of 4 ppm (10 mg/m3)

OSHA: The Occupational Safety and Health Administration has set a Permissible Exposure Limit (PEL) for nitric acid of TWA 2 ppm (5 mg/m3)

Australia [2]

Safe Work Australia: Safe Work Australia has established a time weighted average concentration of less than 5.2 milligrams per cubic metre of air in an 8-hour period. Short-term exposure over a 15-minute period of no more than 10 mg/m3 air is recommended.