UN 1975 — Nitric oxide and dinitrogen tetroxide mixture
Placard: Toxic Gas. ERG Guide 124. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 1975 is Nitric oxide and dinitrogen tetroxide mixture, a toxic corrosive oxidizing gas mixture assigned to ERG Guide 124. It can support combustion and form corrosive nitric/nitrous acids with moisture.
Hazard overview: TOXIC, CORROSIVE and OXIDIZING nitrogen oxide gas/liquefied gas mixture; inhalation may be fatal. Does not burn, but supports combustion and can ignite or intensify burning of combustibles. Reacts with water or moisture to form nitric and nitrous acids, creating corrosive fumes and runoff.
Response guidance: For a UN 1975 incident, verify the product with shipping papers, container markings, SDS and ERG Guide 124. Establish incident command, isolate the area, stay upwind, control ignition or downwind hazards, cool exposed containers from a protected distance when appropriate and base entry decisions on monitoring and local SOP.
Firefighter training notes: Training for UN 1975 should emphasize toxic oxidizing gas behavior, nitric/nitrous acid formation with moisture, Table 1 protective actions, Level A entry decisions and downwind monitoring. Use ERG 124, SDS and local SOP.
Regulatory context: Nitric oxide and dinitrogen tetroxide mixture is regulated as a hazardous material for transportation and emergency response purposes. Storage, workplace exposure, emergency planning, spill reporting and waste handling requirements vary by exact product, concentration, quantity and jurisdiction. Verify current requirements through shipping papers, SDS, container markings and applicable DOT, OSHA, EPA, NFPA, state or local authority guidance.
Storage & handling: Nitric oxide and dinitrogen tetroxide mixture should be stored in compatible containers in a secure, cool, ventilated hazardous-material area according to SDS and local procedures.
UN 1975 Quick Details
Common Hazards of UN 1975
- TOXIC, CORROSIVE and OXIDIZING nitrogen oxide gas/liquefied gas mixture; inhalation may be fatal.
- Does not burn, but supports combustion and can ignite or intensify burning of combustibles.
- Reacts with water or moisture to form nitric and nitrous acids, creating corrosive fumes and runoff.
- Reddish-brown nitrogen dioxide-type vapors are heavier than air and may collect in low areas.
- Contact with gas or liquefied gas may cause chemical burns, severe injury and/or frostbite.
- Fire or heat may produce irritating, corrosive and/or toxic gases.
- Containers may rupture or rocket when heated.
Chemical Identity & Physical Properties
Reddish-brown to yellow-brown gas or liquefied gas mixture with a sharp, acrid, irritating odor. The mixture contains colorless nitric oxide (NO) and red-brown nitrogen tetroxide (N2O4). Heavier than air as a gas.
| Also known as | Nitric oxide/nitrogen tetroxide mixtureNO/N2O4 mixtureNitrogen oxide mixtureMON (Mixed Oxides of Nitrogen)Red fuming nitric acid oxidizer component |
| Appearance | Reddish-brown to yellow-brown gas or liquefied gas mixture with a sharp, acrid, irritating odor. The mixture contains colorless nitric oxide (NO) and red-brown nitrogen tetroxide (N2O4). Heavier than air as a gas. |
| Flash Point | Not applicable (oxidizing gas mixture, not flammable itself but supports combustion) |
| Boiling Point | Approximately 21C (70F) for N2O4 component; mixture boiling point varies with composition |
| Vapor Density | Approximately 1.6-3.2 (heavier than air, depending on mixture ratio) |
| Water Reactivity | Reacts with water to form nitric acid and nitrous acid, highly corrosive. Reaction generates heat and toxic/corrosive fumes. |
Fireground Response Guidance — UN 1975
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA and fully encapsulating chemical protective clothing for close entry or unknown concentrations. Level A may be needed because the gas is toxic, corrosive and oxidizing.
Isolation & Evacuation
First Actions for a UN 1975 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, gas, smoke, mist or dust and avoid skin or eye contact.
- Keep fuels, oils, combustibles and reducing agents away from the release; use Table 1/protective-action guidance where applicable.
- Do not touch damaged containers or spilled/released material unless properly trained and wearing appropriate protective equipment.
- Ventilate closed spaces before entering, but only if properly trained, equipped, monitored and authorized by incident command.
- Isolate the release or spill area and expand the perimeter for fire involvement, vapor accumulation, cylinder/tank heating or unknown product identity.
- Use ERG Guide 124, shipping papers, SDS, air monitoring and incident command for protective actions.
📋 Copy & Share Field Card
UN 1975 — Nitric oxide and dinitrogen tetroxide miUse 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.