UN 3398 — Organometallic substance, liquid, water-reactive
Placard: Dangerous When Wet. ERG Guide 135. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 3398 is Organometallic substance, liquid, water-reactive, a broad organometallic entry assigned to ERG Guide 135. The main concern is water-reactive flammable gas generation; exact compound/SDS verification is critical.
Hazard overview: WATER-REACTIVE organometallic liquid; water or moist air can release flammable gas and heat. May ignite on contact with moisture or if heated by reaction. Some products may also be pyrophoric or transported in flammable solvent; verify SDS before close action.
Response guidance: For UN 3398, isolate the area, keep all water/moisture away and use SCBA from a protected position. Use compatible dry media only and watch for re-ignition under ERG 135.
Firefighter training notes: Training for UN 3398 should emphasize pyrophoric/water-reactive behavior, dry-media tactics, re-ignition checks, moisture exclusion, SCBA use and runoff/debris control. Use ERG 135, SDS and local SOP.
Regulatory context: Organometallic substance, liquid, water-reactive is regulated as a hazardous material for transport and emergency response. Storage, reporting, exposure, waste and incident-notification duties depend on quantity, concentration, formulation and jurisdiction; verify shipping papers, SDS and authority guidance.
Storage & handling: Organometallic substance, liquid, water-reactive should be stored dry in compatible sealed containers under inert gas or approved protective liquid where required, away from water, moisture, air, heat, ignition sources and oxidizers.
UN 3398 Quick Details
Common Hazards of UN 3398
- WATER-REACTIVE organometallic liquid; water or moist air can release flammable gas and heat.
- May ignite on contact with moisture or if heated by reaction.
- Some products may also be pyrophoric or transported in flammable solvent; verify SDS before close action.
- Water, foam, CO2 and halogenated agents may worsen reaction or spread burning material.
- May re-ignite after apparent extinguishment if residue remains reactive.
- Fire may produce toxic metal oxide fumes and irritating organic smoke.
- Exact compound and solvent/wetting condition control fire behavior and PPE.
Chemical Identity & Physical Properties
Varies widely depending on specific compound; typically colorless to pale yellow liquids with characteristic organic or metallic odors. Many are spontaneously flammable in air.
| Also known as | Organometallic compound liquidOrganometallic solutionWater-reactive organometallic liquidPyrophoric organometallic substance |
| Appearance | Varies widely depending on specific compound; typically colorless to pale yellow liquids with characteristic organic or metallic odors. Many are spontaneously flammable in air. |
| Flash Point | Not applicable (spontaneously combustible) |
| Boiling Point | Varies by specific compound |
| Vapor Density | Typically >1 (heavier than air) |
| Water Reactivity | Reacts violently with water, producing flammable gases and heat. May ignite spontaneously. DO NOT use water. |
Fireground Response Guidance — UN 3398
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA with fire/chemical protection and distance from reactive material. Level A or B may be needed for unknown compound, vapor, splash or residue contact.
Isolation & Evacuation
First Actions for a UN 3398 Incident
- Call 911 and the emergency response number on the shipping paper, if available.
- Keep unauthorized personnel away and establish incident command.
- Stay upwind, uphill and upstream.
- Exclude water, moisture, foam and incompatible extinguishing media.
- Avoid disturbing residue because pyrophoric or water-reactive material may re-ignite.
- Avoid breathing vapor, dust, mist, smoke or fumes and avoid skin or eye contact.
- Do not touch damaged containers or spilled material without proper training and PPE.
- Prevent contaminated liquid, dust, runoff and decontamination waste from spreading.
- Ventilate confined spaces only after monitoring and only if properly trained and equipped.
- Use ERG Guide 135, SDS, shipping papers and monitoring to set isolation, evacuation and entry decisions.
📋 Copy & Share Field Card
UN 3398 — Organometallic substance, liquid, water-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.