Nitric acid is one of the most important inorganic acids used in modern industry. It supports fertilizer production, metal processing, chemical synthesis, and the manufacture of energetic materials, while also posing acute risks to workers, equipment, and the environment. 

From an OSHA standpoint, nitric acid must be treated as a substance that requires disciplined hazard communication, strict exposure control, compatible storage, and emergency readiness. Its corrosive nature, oxidizing power, and fuming behavior make it a substance that can injure workers quickly if normal controls fail. 

Nitric Acid Unveiled 

Nitric acid is a core industrial chemical with enormous value and equally serious hazards. Under OSHA's chemical data, it is a highly corrosive, strongly oxidizing acid with an 8-hour permissible exposure limit of 2 ppm and a very severe NFPA health rating of 4. 

Chemical identity 

Nitric acid has the formula HNO₃ and CAS number 7697-37-2. OSHA also recognizes common synonyms such as "aqua fortis," "spirit of niter," "engravers' acid," "white fuming nitric acid," "red fuming nitric acid," and "hydrogen nitrate." 

It is a colorless, yellow, or red fuming liquid with an acrid, suffocating odor. The physical profile changes with concentration, impurity level, and dissolved nitrogen oxides, which is why white fuming and red fuming grades are handled as specialized high-hazard materials. 

1. Core properties 

Nitric acid is a strong mineral acid and a powerful oxidizer. It is not just corrosive in the usual acid sense; it can also intensify combustion, react violently with reducing agents, and generate toxic nitrogen oxide vapors. 

Its boiling point is 181 F, the freezing point is -44 F, specific gravity is 1.5, and vapor pressure is 48 mmHg. Those properties help explain why it can release irritating vapors readily and why temperature control matters during storage and transfer.

2. OSHA exposure limits 

OSHA's chemical data lists a PEL of 2 ppm as an 8-hour time-weighted average for nitric acid. The same page also identifies a NIOSH recommended exposure limit of 2 ppm TWA and 4 ppm STEL, plus an ACGIH TLV of 2 ppm TWA and 4 ppm STEL. 

Those numbers are not paperwork only; they define the practical boundary between controlled work and unacceptable airborne exposure. In real operations, you should assume that visible fuming, poor ventilation, or a strong sharp odor means controls are inadequate even before a monitor confirms it.

Health hazards 

Nitric acid can cause severe chemical burns, rapid tissue destruction, and serious respiratory injury. OSHA's listed NFPA health rating of 4 reflects the potential for extreme acute harm, especially from concentrated liquid or vapor exposure. 

Inhalation is particularly concerning because vapors and nitrogen oxide decomposition products can injure the respiratory tract and, in severe cases, contribute to pulmonary edema. The hazard is not limited to direct splash contact; even brief exposure in a poorly ventilated area can be dangerous. 

Corrosive and oxidizing behavior 

The corrosive action of nitric acid comes from its ability to destroy tissue and denature proteins. The familiar yellow staining skin after exposure is a warning sign, but it should never be mistaken for a benign injury because deeper damage may already be present. 

Its oxidizing behavior creates additional risk around flammables, organics, fuels, oils, and many reducing chemicals. Incompatible contact can generate heat, toxic gases, or fire conditions, so segregation is a primary control rather than an optional storage preference. 

HazCom and SDS use 

Under OSHA's Hazard Communication framework, workers must be trained on the hazards of chemicals they may encounter and have access to current safety data before use. For nitric acid, the SDS should be treated as an operational document, not a filing requirement, because it contains key information on exposure controls, incompatibilities, first aid, and spill response. 

A strong SDS review for nitric acid should focus on the sections covering hazard identification, composition, first aid, firefighting, accidental release measures, handling and storage, exposure controls, and physical and chemical properties. In practice, no transfer, dilution, or cleaning task should begin unless the applicable SDS is accessible to the people doing the work. 

Production overview 

Industrial nitric acid is generally produced by the Ostwald process, which oxidizes ammonia over a platinum or rhodium catalyst to form nitrogen monoxide, then nitrogen dioxide, and finally nitric acid through absorption in water. This route is the basis of large-scale global supply because it is efficient and integrates well with fertilizer manufacturing. 

From a workplace safety perspective, large-scale production adds additional hazards beyond nitric acid itself, including high-temperature process equipment, nitrogen oxide emissions, and corrosion management in reactors, absorbers, and storage systems. Those process hazards are why plant design, preventive maintenance, and emission controls are as important as chemistry itself. 

Assorted Usage of Nitric Acid 

Nitric acid is a widely used industrial chemical with major applications in fertilizer production, metal processing, organic synthesis, and the manufacture of energetic materials.

• Agriculture uses 

Nitric acid is central to fertilizer production, especially ammonium nitrate manufacturing. Its role in the nitrogen economy makes it one of the most strategically important acids in global agriculture. 

The neutralization reaction with ammonia produces ammonium nitrate, a major nitrogen fertilizer precursor: 

NH₃ + HNO₃ → NH₄NO₃ 

At an industrial scale, this process must be controlled carefully because the product, intermediate solutions, and associated process conditions can all present separate hazards. Fertilizer production also requires strict contamination control because impurity and moisture management affect product quality and safety. 

• Metal processing uses 

In metallurgy, nitric acid is used for stainless steel passivation, metal cleaning, and etching. Passivation removes free iron from the surface and supports the development or restoration of a protective chromium-rich oxide layer. 

It is also used in etching applications where controlled attack on a metal surface is needed for marking, texturing, or preparatory treatment. Because nitric acid can attack metals aggressively, compatibility must be verified for every vessel, fitting, line, and tool that may come into contact with it. 

• Precious metal refining 

Nitric acid is a key component in aqua regia chemistry, where it works with hydrochloric acid to dissolve certain noble metals for refining and analytical purposes. The mixture is highly aggressive and generates toxic gases, so it belongs only in controlled operations with robust ventilation and trained personnel. 

Aqua regia work should be treated as a specialized chemical operation with a distinct hazard assessment, not as a routine bench-scale acid task. The compatibility of glassware, exhaust systems, waste containers, and neutralization procedures must be confirmed before the work begins. 

• Organic synthesis 

Nitric acid is widely used in nitration reactions to introduce nitro groups into organic molecules. That chemistry supports the manufacture of dyes, intermediates, pharmaceutical building blocks, and performance materials. 

Because nitration can be highly exothermic and can create unstable intermediates, process control is essential. Temperature control, feed rate control, emergency quench planning, and reaction calorimetry are common safeguards in serious production environments. 

• Explosives and energetic materials 

Nitric acid is involved in the production of energetic compounds such as nitroglycerin and TNT. These applications are tightly regulated because the chemistry is intrinsically high risk and because the products themselves are sensitive and hazardous. 

Facilities handling such materials need layered controls, including secure access, process interlocks, segregation of raw materials, blast-resistant design where applicable, and emergency response procedures tailored to energetic material incidents. For OSHA purposes, the main point is that nitric acid oxidizing power makes it a significant upstream hazard in these operations. 

PPE and engineering controls 

PPE should never be the only defense against nitric acid exposure. OSHA's exposure framework implies that engineering controls, especially local exhaust ventilation and enclosed transfer systems, should be the first line of protection whenever practical. 

For direct handling, use chemical splash goggles and a face shield, acid-resistant clothing, and gloves selected for documented compatibility. Butyl rubber and neoprene are often better choices than general-purpose gloves for strong acids, while glove selection should be confirmed with the manufacturer's chemical resistance data before use. 

1. Respiratory protection 

Nitric acid vapors and decomposition fumes can be dangerous even when the liquid is not directly contacted. A fume hood or similarly effective local exhaust system is the preferred control for open handling. 

If respirator use is necessary, it must be part of a formal respiratory protection program with proper hazard assessment, fit testing, medical clearance, training, and cartridge selection. Respiratory protection should be viewed as a backup control, not a substitute for ventilation or containment. 

2. Storage and stability 

Nitric acid should be stored in a cool, dry, well-ventilated area away from sunlight and heat sources. Temperature management matters because heating can increase pressure, vapor release, and degradation risk. 

Containers must be clearly labeled and kept tightly closed when not in use. Secondary containment is strongly advisable, especially in facilities where a leak could reach incompatible chemicals, drains, or occupied spaces. 

3. Incompatibilities 

Nitric acid must be segregated from bases, reducing agents, flammables, combustible organics, fuels, oils, and many solvents. Its oxidizing action can intensify fire or create violent reactions when the wrong materials are nearby. 

Container compatibility must be verified before storage or transfer. High-density polyethylene, certain stainless steels, and glass may be suitable in some applications, but compatibility depends on concentration, temperature, and service conditions; no single material should be assumed safe without validation. 

4. Exposure first aid 

If nitric acid contacts skin or eyes, immediate flushing with water is critical. Continued irrigation for at least 15 minutes is a common minimum response, but eye exposure or significant skin contact warrants urgent medical evaluation even after the initial wash. 

Contaminated clothing should be removed while rinsing, taking care not to spread the chemical. Inhalation exposure requires moving the person to fresh air and obtaining emergency medical help without delay. 

5. Spill response 

Small spills can sometimes be neutralized cautiously with agents such as sodium bicarbonate or lime, followed by absorption with inert material and collection as hazardous waste. Neutralization should be done slowly because the reaction can release heat and gas. 

Large spills require evacuation, isolation, and a trained hazmat response. In a facility setting, the response plan should already define alarm criteria, exclusion zones, communications, and waste disposal pathways before any incident occurs.

Environmental impact 

Nitric acid and nitrogen oxide emissions are major contributors to acidification risks in air and water systems. Atmospheric nitrogen oxides can form nitric acid and contribute to acid rain, while direct releases can sharply lower water pH and mobilize metals. 

Industrial emission controls such as scrubbers, monitoring systems, and waste neutralization are therefore central compliance tools. Environmental protection is not separate from worker safety here; it is part of the same control strategy. 

Transport and labeling 

Nitric acid is typically managed as a corrosive hazardous material in transportation and storage systems. Shipping requires proper packaging, placarding, documentation, and trained handlers who understand both corrosive and oxidizing hazards. 

Drivers and warehouse personnel should be trained to recognize the material's reactivity, segregate it from incompatible cargo, and respond to leaks without improvisation. A shipping incident involving nitric acid can escalate quickly if responders do not understand that the chemical is both corrosive and oxidizing. 

Operating practices 

A strong nitric acid program should include a written risk assessment, pre-job review, SOPs for transfer and dilution, local exhaust ventilation, emergency eyewash and shower access, inspection of containers and fittings, and periodic training. These controls are especially important where workers handle concentrated or fuming grades. 

Good practice also means using the smallest practical quantity, keeping incompatible chemicals out of the work area, and verifying that waste containers are correctly labeled and segregated. For higher-risk tasks, a second person check or permit-style authorization may be appropriate.