UN 2031 — Nitric acid, other than red fuming, with not more than 65% nitric acid
Placard: Corrosive. ERG Guide 157. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 2031 is Nitric acid, other than red fuming, with not more than 65% nitric acid, a Class 8 corrosive liquid assigned to ERG Guide 157. It is a strong acid and oxidizer that can cause severe burns, toxic fume exposure and dangerous reactions with incompatible materials.
Hazard overview: UN 2031 presents corrosive, toxic vapor and oxidizer hazards. Nitric acid can severely burn skin, eyes and respiratory tissue, while fumes may include hazardous nitrogen oxides. Although the acid itself is not flammable, it can intensify fire and react with organic materials, fuels, metals and reducing agents, sometimes producing heat, toxic gases or flammable hydrogen.
Response guidance: For a UN 2031 incident, responders should confirm concentration and product identity using shipping papers, container markings, SDS and ERG Guide 157. Establish incident command, isolate the area, stay upwind and uphill, avoid liquid or vapor contact, keep combustibles and incompatible materials away, use water cautiously from a protected position, and control corrosive runoff under local SOP.
Firefighter training notes: Training should emphasize nitric acid as both a strong corrosive and an oxidizer. Common tactical errors include treating the incident like a simple acid spill, allowing contact with fuels or organic materials, applying water without considering heat and runoff, and failing to monitor for nitrogen oxide fumes. Incident command should coordinate isolation, air monitoring, oxidizer segregation, decontamination, runoff control and hazmat technician support under local SOP.
Regulatory context: Nitric acid under UN 2031 is regulated as a Class 8 corrosive hazardous material and may also carry oxidizer-related controls depending on concentration and shipment details. Workplace exposure, transportation, spill reporting, waste handling and environmental requirements may apply. Responders should verify current requirements through shipping papers, SDS, facility documents and applicable DOT, OSHA, EPA, state or local authority guidance.
Storage & handling: Nitric acid should be stored in compatible, tightly closed containers in a cool, dry and well-ventilated area with corrosion-resistant secondary containment. Keep it away from organic materials, fuels, reducing agents, bases, many metals, powders and other incompatible chemicals. Storage areas should be protected from heat, contamination, physical damage and drain pathways.
UN 2031 Quick Details
Common Hazards of UN 2031
- TOXIC and/or CORROSIVE; inhalation, ingestion or skin and eye contact with vapors, mist or liquid may cause severe injury.
- Nitric acid can cause severe chemical burns to skin, eyes and respiratory tissue.
- Strong oxidizer; may intensify fire and react dangerously with organic materials, fuels, reducing agents and some metals.
- Reaction with water, moisture or incompatible materials may generate heat and increase corrosive fuming.
- Contact with metals may release toxic nitrogen oxides and, in some cases, flammable hydrogen gas.
- Fire may produce irritating, corrosive and/or toxic gases, including nitrogen oxides.
- Runoff from fire control or dilution water may be corrosive or toxic and may cause environmental contamination.
- Vapors are heavier than air and may accumulate in low or poorly ventilated areas.
Chemical Identity & Physical Properties
Nitric acid solution is typically a colorless to pale yellow fuming liquid with a sharp, acrid odor. Vapors are heavier than air, the liquid is corrosive to tissue and many metals, and fuming may increase with heat, moisture or contamination.
| Also known as | Aqua fortisHydrogen nitrateAzotic acidWhite fuming nitric acidWFNANitric acid solution |
| CAS Number | 7697-37-2 |
| Appearance | Colorless to pale yellow fuming liquid with a suffocating, acrid, pungent odor. Fumes in moist air. Corrosive to metals and tissue. |
| Flash Point | Not applicable (strong oxidizer, non-flammable but supports combustion) |
| Boiling Point | 83C (181F) for concentrated solutions; varies with concentration |
| Vapor Density | 2.2 (heavier than air) |
| Water Reactivity | Highly exothermic reaction with water; generates heat and may increase fuming. Dilute slowly by adding acid to water, never reverse. |
Fireground Response Guidance — UN 2031
Extinguishing Media
PPE Requirements
Responders should use positive-pressure SCBA and acid-resistant chemical protective clothing when exposure to vapor, mist or liquid is possible. Gloves, boots, face protection and suit material should be selected using ERG 157, SDS, concentration, monitoring results, incident command and local SOP.
Isolation & Evacuation
First Actions for a UN 2031 Incident
- CALL 911. Then call the emergency response telephone number on the shipping paper, if available.
- Keep unauthorized personnel away.
- Stay upwind, uphill and/or upstream.
- Avoid breathing vapors, mist or fire gases.
- Do not touch damaged containers or spilled material unless properly trained and wearing appropriate protective equipment.
- Keep nitric acid away from organic materials, fuels, reducing agents, metals and other incompatible substances.
- Ventilate closed spaces before entering, but only if properly trained, equipped and authorized by incident command.
- Isolate the spill or leak area in all directions for at least 50 meters (150 feet) for liquids.
- For highlighted materials, consult ERG Table 1 for Initial Isolation and Protective Action Distances.
- For non-highlighted materials, increase the immediate precautionary distance as needed in the downwind direction based on vapor, fume, fire or spill conditions.
📋 Copy & Share Field Card
UN 2031 — Nitric acid, other than red fuming, withUse for: Quick radio or face-to-face size-up. Short, structured, field-ready.
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief.
Use for: Quick text to command or incoming units. Fits in a single SMS.