Nitric Acid

Classification

Oxidizing liquid, Category 3; Corrosive to metals, Category 1; Acute toxicity (inhalation), Category 3; Skin corrosion, Category 1A; Serious eye damage, Category 1 (per the Sigma-Aldrich SDS for 60–80% nitric acid). Classification varies with concentration, so check your supplier's safety data sheet.

Hazard statements

• H272 May intensify fire; oxidizer.
• H290 May be corrosive to metals.
• H314 Causes severe skin burns and eye damage.
• H331 Toxic if inhaled.
• EUH071 Corrosive to the respiratory tract.

Key precautionary statements

• P210 Keep away from heat, hot surfaces, sparks, open flames and other ignition sources. No smoking.
• P261 Avoid breathing mist or vapors.
• P271 Use only outdoors or in a well-ventilated area.
• P280 Wear protective gloves, protective clothing, eye protection and face protection.
• P301+P330+P331 IF SWALLOWED: Rinse mouth. Do NOT induce vomiting.
• P303+P361+P353 IF ON SKIN (or hair): Take off immediately all contaminated clothing. Rinse skin with water.
• P304+P340+P310 IF INHALED: Remove person to fresh air and keep comfortable for breathing. Immediately call a POISON CENTER or doctor.
• P305+P351+P338+P310 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing. Immediately call a POISON CENTER or doctor.
• P406 Store in a corrosion-resistant container.

OSHA sets a 2 ppm (5 mg/m³) 8-hour TWA for general industry (29 CFR 1910.1000 Table Z-1), construction and shipyards. NIOSH, ACGIH and Cal/OSHA all use 2 ppm TWA with a 4 ppm STEL. The NIOSH IDLH is 25 ppm. No skin notation is assigned, but skin contact with the liquid causes burns regardless of air levels. Nitric acid often releases nitrogen dioxide, which has its own exposure limits, so measure both where fumes are visible. State OSHA plans may set different limits.

• Appearance: Colorless to yellow liquid; fuming grades are yellow to red-brown
• Odor: Acrid, suffocating
• Molecular weight: 63.0
• Boiling point: 181°F (83°C)
• Freezing point: -44°F (-42°C)
• Flash point: Not flammable, but increases the flammability of combustible materials
• Explosive limits: Not applicable
• Vapor pressure: 48 mmHg
• Specific gravity: 1.50 at 77°F (sinks in and mixes with water)
• Water solubility: Miscible; mixing with water gives off heat

Physical data are for concentrated nitric acid (NIOSH); diluted grades differ.

Inhalation

Vapors and mists irritate the nose, throat and lungs, causing cough and shortness of breath. Higher exposures, including to the nitrogen oxides it releases, can cause fluid in the lungs (pulmonary edema), which may not appear for several hours.

Skin

Causes severe burns that stain the skin yellow. See burn injury.

Eyes

Causes severe burns and can cause permanent eye damage.

Ingestion

Burns the mouth, throat and stomach. Get emergency medical help immediately.

Target organs

Eyes, skin, respiratory system, teeth

Long-term effects

Repeated exposure to mists can erode the teeth and may cause bronchitis.

Gloves

NJDOH lists butyl, neoprene, Silver Shield/4H, Viton and Barrier gloves, and Barrier only for fuming nitric acid. Check the maker's data for your concentration. See hand protection.

Eyes and face

Chemical splash goggles plus a face shield. Provide an eyewash station and safety shower in the work area.

Respiratory

Handle in a fume hood or with local exhaust ventilation. Up to 25 ppm, NIOSH lists full-facepiece respirators with suitable acid gas cartridges, gas masks, continuous-flow supplied-air respirators or SCBA. Above 25 ppm or at unknown levels, use a pressure-demand full-facepiece SCBA. See respiratory protection.

Clothing

Acid-resistant apron or suit; NJDOH lists Tychem CPF3, F, BR, Responder and TK and Trellchem HPS and VPS. Remove contaminated clothing immediately; nitric acid can ignite cotton and other combustibles.

Store in tightly closed, acid-resistant containers in a cool, dry, well-ventilated area out of direct light, with secondary containment. Keep separate from organic materials, combustibles and other acids such as acetic acid.

When diluting, add acid slowly to water, never water to acid, because mixing gives off heat. Do not use wood shelving or organic absorbents near nitric acid.

Keep away from

• Combustible and organic materials, including alcohols and solvents such as acetone
• Metal powders, alkali metals and metal hydrides
• Strong bases such as sodium hydroxide
• Hydrogen sulfide, sulfides, cyanides and carbides
• Ammonia and amines

• Evacuate the area and ventilate. Responders need respiratory protection, goggles, face shield and acid-resistant clothing.
• Keep combustible materials away from the spill; do not use sawdust or other organic absorbents.
• Absorb with dry sand, earth or another non-combustible material and place in closed containers for disposal.
• Neutralize residue with sodium carbonate or a mild alkali.
• Keep out of drains and waterways.
• Follow ERG Guide 157 (UN2031).

Suitable extinguishing media

• Nitric acid does not burn but feeds fires in other materials
• Flooding amounts of water
• Water spray to cool containers and knock down vapors
• Do not use dry chemical or foam extinguishers on nitric acid itself

Special hazards

A strong oxidizer that can ignite wood, paper, cloth and other combustibles. Fires and reactions with metals give off toxic nitrogen oxides such as nitrogen dioxide. Firefighters should wear SCBA and acid-resistant gear.

• OSHA Hazard Communication (29 CFR 1910.1200): Hazardous chemical; SDS, labels and training required.
• OSHA Air Contaminants (29 CFR 1910.1000 Table Z-1): 2 ppm (5 mg/m³) TWA.
• OSHA Process Safety Management (29 CFR 1910.119 Appendix A): Nitric acid at 94.5% by weight or greater, threshold quantity 500 lb.
• CERCLA (40 CFR 302.4): Hazardous substance, reportable quantity 1,000 lb.
• EPCRA Section 302 (40 CFR 355 Appendix A): Extremely hazardous substance, threshold planning quantity 1,000 lb, reportable quantity 1,000 lb.
• Clean Air Act 112(r) (40 CFR 68.130): Nitric acid at 80% or greater, threshold quantity 15,000 lb. Not a listed hazardous air pollutant.
• DOT (49 CFR 172.101): UN2031, Nitric acid, Class 8, with a 5.1 oxidizer label at 65% or more; PG II per supplier SDS. Red fuming nitric acid ships as UN2032.

• NIOSH Pocket Guide: Nitric acid
• OSHA Occupational Chemical Database: Nitric acid
• Sigma-Aldrich SDS: Nitric acid
• NJ Department of Health Hazardous Substance Fact Sheet: Nitric Acid
• CAMEO Chemicals: UN2031 (DOT and ERG data)
• 40 CFR 355 Appendix A, EPCRA extremely hazardous substances
• OSHA 29 CFR 1910.119 Appendix A, highly hazardous chemicals