UN 3399 — Organometallic substance, liquid, water-reactive, flammable
Placard: Dangerous When Wet. ERG Guide 138. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 3399 is Organometallic substance, liquid, water-reactive, flammable, a broad organometallic entry assigned to ERG Guide 138. The main concern is water-reactive gas generation plus flammable behavior; exact compound/SDS verification is critical.
Hazard overview: WATER-REACTIVE and FLAMMABLE organometallic liquid; moisture can release flammable gases and heat. May ignite on contact with water, moist air, heat, sparks or flames. If solvent is present, vapors may travel to ignition sources and flash back.
Response guidance: For UN 3399, 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 138.
Firefighter training notes: Training for UN 3399 should emphasize pyrophoric/water-reactive behavior, dry-media tactics, re-ignition checks, moisture exclusion, SCBA use and runoff/debris control. Use ERG 138, SDS and local SOP.
Regulatory context: Organometallic substance, liquid, water-reactive, flammable 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, flammable 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 3399 Quick Details
Common Hazards of UN 3399
- WATER-REACTIVE and FLAMMABLE organometallic liquid; moisture can release flammable gases and heat.
- May ignite on contact with water, moist air, heat, sparks or flames.
- If solvent is present, vapors may travel to ignition sources and flash back.
- Water, foam, CO2 and halogenated agents can worsen reaction or spread burning material.
- May re-ignite after apparent extinguishment.
- Fire may produce toxic metal oxide fumes, carbon monoxide and irritating organic smoke.
- Exact compound, solvent and package condition must be verified from SDS and shipping papers.
Chemical Identity & Physical Properties
Varies by specific compound; typically colorless to pale yellow liquid with distinctive odor. Many are spontaneously flammable in air and react violently with moisture.
| Also known as | Organometallic liquidWater-reactive organometallic compoundPyrophoric organometallic liquidMetal-organic compound liquid |
| Appearance | Varies by specific compound; typically colorless to pale yellow liquid with distinctive odor. Many are spontaneously flammable in air and react violently with moisture. |
| Flash Point | Not applicable (spontaneously flammable in air) |
| Boiling Point | Varies by compound (typically 50-150C range) |
| Vapor Density | Heavier than air (typically 2-5 times air density) |
| Water Reactivity | Reacts violently with water producing flammable gases; may ignite spontaneously on contact with moisture |
Fireground Response Guidance — UN 3399
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 3399 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 138, SDS, shipping papers and monitoring to set isolation, evacuation and entry decisions.
📋 Copy & Share Field Card
UN 3399 — 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.