UN 3503 — Chemical under pressure, corrosive, n.o.s.
Placard: Non-Flammable Gas. ERG Guide 125. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 3503 is Chemical under pressure, corrosive, n.o.s., a pressurized hazardous material assigned to ERG Guide 125. The exact contents should be verified from shipping papers and the SDS before close-range action.
Hazard overview: Primary hazards include toxic exposure, corrosive burns, fire or vapor ignition, container rupture. Chemical under pressure, corrosive, n.o.s. may release irritating, toxic or corrosive vapors when heated, spilled or involved in fire, so avoid contact, inhalation and incompatible materials.
Response guidance: For a UN 3503 incident, establish incident command, isolate the area, stay upwind and uphill, keep unauthorized personnel away, verify shipping papers/SDS and follow ERG 125. Use extinguishing, cooling, containment and decontamination tactics only when compatible with the material and local SOP.
Firefighter training notes: Training should emphasize pressure-container recognition, corrosive vapor exposure, frostbite from liquefied gas and product identification for n.o.s. entries. Common tactical errors include approaching damaged cylinders too early, assuming non-flammable means low hazard, using water or foam without checking compatibility, and entering low or confined areas before monitoring. Incident command should coordinate isolation, air monitoring, cylinder assessment, PPE selection, leak control and specialist hazmat support under local SOP.
Regulatory context: UN 3503 is regulated as a Class 2 chemical under pressure with corrosive hazards. Transportation, workplace exposure, pressure-container, spill reporting and environmental requirements may vary based on the specific chemical mixture and jurisdiction. Responders should verify current requirements through shipping papers, SDS, container markings, facility documents and applicable DOT, OSHA, EPA, state or local authority guidance.
Storage & handling: Chemical under pressure, corrosive, n.o.s. should be stored in approved pressure containers or cylinders in a cool, dry and well-ventilated area. Keep containers away from heat, physical damage, incompatible chemicals, direct sunlight and unauthorized access. Storage controls should follow the product SDS, pressure-container requirements, segregation rules and local facility SOP.
UN 3503 Quick Details
Common Hazards of UN 3503
- TOXIC and/or CORROSIVE; may be fatal if inhaled or absorbed through skin.
- Vapors are extremely irritating and corrosive to eyes, skin and the respiratory tract.
- Contact with gas, liquefied gas or pressurized liquid may cause burns, severe injury and/or frostbite.
- Pressurized containers may rupture or explode when heated.
- Fire may produce irritating, corrosive and/or toxic gases.
- Runoff from fire control or dilution water may cause environmental contamination.
- Vapors from liquefied gas may initially be heavier than air and spread along the ground.
- Water reactivity, flammability and decomposition hazards vary by the specific chemical under pressure.
Chemical Identity & Physical Properties
Variable appearance depending on specific chemical; may be colorless to colored gas or liquefied gas under pressure. Contact with liquefied gas causes frostbite. Vapors are extremely irritating and corrosive to eyes, skin, and respiratory tract.
| Also known as | Compressed corrosive chemicalPressurized corrosive substanceAerosol corrosive chemicalCorrosive gas under pressure |
| Appearance | Variable appearance depending on specific chemical; may be colorless to colored gas or liquefied gas under pressure. Contact with liquefied gas causes frostbite. Vapors are extremely irritating and corrosive to eyes, skin, and respiratory tract. |
| Flash Point | Not applicable (pressurized gas mixture) |
| Boiling Point | Variable depending on specific chemical and pressure |
| Vapor Density | Variable; typically heavier than air for corrosive gases |
| Water Reactivity | Variable depending on specific chemical; may react violently with water or moisture producing corrosive vapors |
Fireground Response Guidance — UN 3503
Extinguishing Media
PPE Requirements
Level A required for unknown corrosive gases; full encapsulating suit with SCBA; avoid all contact with gas or liquid; extreme inhalation and skin contact hazard
Isolation & Evacuation
First Actions for a UN 3503 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 gas, vapor, mist or fire gases.
- Do not touch damaged cylinders, pressure containers or released material unless properly trained and wearing appropriate protective equipment.
- Many gases may spread along the ground when released cold from liquefied gas and may collect in low or confined areas.
- Ventilate closed spaces before entering, but only if properly trained, equipped and authorized by incident command.
- Isolate the spill or leak area for at least 100 meters (330 feet) in all directions.
- 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 the specific chemical, container condition and monitoring results.
📋 Copy & Share Field Card
UN 3503 — Chemical under pressure, corrosive, n.o.Use 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.