☣️ UN 1975 • CLASS 2
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.
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⚠️ This page is a quick-reference aid. For real incidents: stage upwind, isolate, deny entry, request Hazmat early, and consult the current ERG + SOP/SOG.
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UN 1975 Quick Details
UN 1975
Product name: Nitric oxide and dinitrogen tetroxide mixture
DOT Class: 2
Placard type: Toxic Gas
ERG Guide: 124 (check current ERG)
Initial isolation: ERG 124: Initial isolation 100m (330 ft) in all directions. Protective action distance: daytime 0.3 km (0.2 mi), nighttime 0.8 km (0.5 mi) for small spills. Large spills: daytime 1.1 km (0.7 mi), nighttime 3.2 km (2.0 mi).
Common Hazards of UN 1975
- TOXIC and/or CORROSIVE; may be fatal if inhaled or absorbed through skin.
- Fire will produce irritating, corrosive and/or toxic gases.
- Contact with gas or liquefied gas may cause burns, severe injury and/or frostbite.
- Runoff from fire control or dilution water may cause environmental contamination.
- Substance does not burn but will support combustion.
- Vapors from liquefied gas are initially heavier than air and spread along ground.
- These are strong oxidizers and will react vigorously or explosively with many materials including fuels.
- May ignite combustibles (wood, paper, oil, clothing, etc.).
Chemical Identity & Physical Properties
| 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. |
Chemical details are general reference only. Always verify with current SDS, ERG, and SOP/SOG.
Fireground Response Guidance — UN 1975
Extinguishing Media
Do not use water directly. Use dry chemical or CO2 for small fires. For large fires, use water spray from a distance to cool containers but avoid direct contact with material.
PPE Requirements
⚠️ Level A required for direct contact or high concentrations. Full-face SCBA mandatory. Fully encapsulating chemical protective suit. Material is extremely toxic by inhalation and highly corrosive to skin and eyes.
Isolation & Evacuation
ERG 124: Initial isolation 100m (330 ft) in all directions. Protective action distance: daytime 0.3 km (0.2 mi), nighttime 0.8 km (0.5 mi) for small spills. Large spills: daytime 1.1 km (0.7 mi), nighttime 3.2 km (2.0 mi).
Always confirm protective actions with the current edition of the Emergency Response Guidebook (ERG Guide 124).
First Actions for a UN 1975 Incident
- CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper
- Keep unauthorized personnel away.
- Stay upwind, uphill and/or upstream.
- Many gases are heavier than air and will spread along the ground and collect in low or confined areas
- Ventilate closed spaces before entering, but only if properly trained and equipped.
- Isolate spill or leak area for at least 100 meters (330 feet) in all directions.
- See Table 1 - Initial Isolation and Protective Action Distances.
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📋 Copy & Share Field Card
UN 1975 — Nitric oxide and dinitrogen tetroxide miHAZMAT RADIO NOTE — UN 1975
Product: Nitric oxide and dinitrogen tetroxide mixture
Class 2 / Toxic Gas / ERG 124
PPE: Level A required for direct contact or high concentrations. Full-face SCBA mandatory. Fully encapsulating chemical protective suit. Material is extremely toxic by inhalation and highly corrosive to skin and eyes.
ISOLATION: ERG 124: Initial isolation 100m (330 ft) in all directions. Protective action distance: daytime 0.3 km (0.2 mi), nighttime 0.8 km (0.5 mi) for small spills. Large spills: daytime 1.1 km (0.7 mi), nighttime 3.2 km (2.0 mi).
ACTION: Stage upwind · Isolate · Deny entry · Request HazmatRADIO
Use for: Quick radio or face-to-face size-up. Short, structured, field-ready.
=== IC HAZMAT BRIEFING ===
UN 1975 — Nitric oxide and dinitrogen tetroxide mixture
Class: 2 | Placard: Toxic Gas | ERG Guide: 124
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.
Water Reactivity: Reacts with water to form nitric acid and nitrous acid, highly corrosive. Reaction generates heat and toxic/corrosive fumes.
Extinguishing: Do not use water directly. Use dry chemical or CO2 for small fires. For large fires, use water spray from a distance to cool containers but avoid direct contact with material.
PPE: Level A required for direct contact or high concentrations. Full-face SCBA mandatory. Fully encapsulating chemical protective suit. Material is extremely toxic by inhalation and highly corrosive to skin and eyes.
Isolation: ERG 124: Initial isolation 100m (330 ft) in all directions. Protective action distance: daytime 0.3 km (0.2 mi), nighttime 0.8 km (0.5 mi) for small spills. Large spills: daytime 1.1 km (0.7 mi), nighttime 3.2 km (2.0 mi).
— Key Hazards —
• TOXIC and/or CORROSIVE; may be fatal if inhaled or absorbed through skin.
• Fire will produce irritating, corrosive and/or toxic gases.
• Contact with gas or liquefied gas may cause burns, severe injury and/or frostbite.
— First Actions —
• CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper
• Keep unauthorized personnel away.
• Stay upwind, uphill and/or upstream.
• Many gases are heavier than air and will spread along the ground and collect in low or confined areas
SOURCE: allfirefighter.com/hazmat/un/1975 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief. Full chemical + response details.
UN1975 Nitric oxide and dinitrogen tetroxide mixture Cls2 ERG124 | allfirefighter.com/hazmat/un/1975SMS / 160 CHAR
Use for: Quick text to command or incoming units. Fits in a single SMS. Includes link to full page.
⚠️ Quick-reference only. Always use current ERG + SOP/SOG for incident-specific actions.
Page: https://allfirefighter.com/hazmat/un/1975
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Frequently Asked Questions about UN 1975
TOXIC and/or CORROSIVE; may be fatal if inhaled or absorbed through skin. Fire will produce irritating, corrosive and/or toxic gases. Contact with gas or liquefied gas may cause burns, severe injury and/or frostbite. Runoff from fire control or dilution water may cause environmental contamination. Substance does not burn but will support combustion. Vapors from liquefied gas are initially heavier than air and spread along ground. These are strong oxidizers and will react vigorously or explosively with many materials including fuels. May ignite combustibles (wood, paper, oil, clothing, etc.).
CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper Keep unauthorized personnel away. Stay upwind, uphill and/or upstream.
Level A required for direct contact or high concentrations. Full-face SCBA mandatory. Fully encapsulating chemical protective suit. Material is extremely toxic by inhalation and highly corrosive to skin and eyes.
Water reactivity: Reacts with water to form nitric acid and nitrous acid, highly corrosive. Reaction generates heat and toxic/corrosive fumes.. Recommended extinguishing: Do not use water directly. Use dry chemical or CO2 for small fires. For large fires, use water spray from a distance to cool containers but avoid direct contact with material..
ERG Guide 124 recommendation: ERG 124: Initial isolation 100m (330 ft) in all directions. Protective action distance: daytime 0.3 km (0.2 mi), nighttime 0.8 km (0.5 mi) for small spills. Large spills: daytime 1.1 km (0.7 mi), nighttime 3.2 km (2.0 mi).
No. This is a training/quick-reference aid only. Always consult the current ERG Guide 124 and your department SOP/SOG for incident-specific protective actions.
Sources (high level): DOT/PHMSA marking & class concepts + ERG usage principles.
This page does not reproduce ERG guide text—always consult the current ERG for incident-specific protective actions.