UN 3525 — Phosphine, adsorbed
Placard: Toxic Gas. ERG Guide 173. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 3525 is Phosphine, adsorbed, a toxic flammable adsorbed phosphine gas assigned to ERG Guide 173. Odor is unreliable and ignition risk is serious.
Hazard overview: EXTREMELY TOXIC phosphine gas adsorbed on a porous solid; inhalation may be fatal. Phosphine is flammable and may ignite spontaneously in air under some conditions. Gas is heavier than air and can collect in low or confined areas.
Response guidance: For UN 3525, isolate downwind/low areas, treat as a life-threatening gas release and use Level A/SCBA for entry. Verify exact gas with shipping papers and ERG 173.
Firefighter training notes: Training for UN 3525 should emphasize toxic-gas recognition, Zone A isolation, Level A/SCBA entry, air monitoring, source-control limits and decontamination. Use ERG 173, SDS and local SOP.
Regulatory context: Phosphine, adsorbed is regulated as a hazardous material for transport and emergency response. Storage, reporting, exposure, waste and incident-notification duties depend on quantity, package type, gas identity and jurisdiction; verify shipping papers, SDS and authority guidance.
Storage & handling: Phosphine, adsorbed should be stored in secured compatible adsorbed-gas packages away from heat, impact, corrosion, moisture where incompatible and unauthorized access, with ventilation and emergency planning.
UN 3525 Quick Details
Common Hazards of UN 3525
- EXTREMELY TOXIC phosphine gas adsorbed on a porous solid; inhalation may be fatal.
- Phosphine is flammable and may ignite spontaneously in air under some conditions.
- Gas is heavier than air and can collect in low or confined areas.
- Odor is not a reliable warning for dangerous concentrations.
- Fire may produce phosphorus oxides and irritating/toxic smoke.
- Heating or package damage can release toxic flammable gas.
- Runoff or debris may be contaminated with phosphorus-containing residue.
Chemical Identity & Physical Properties
Colorless gas with a disagreeable, fish-like or garlic-like odor. Highly toxic and pyrophoric (may ignite spontaneously in air at concentrations above 200 ppm).
| Also known as | Hydrogen phosphidePhosphorus trihydridePH3Phosphane |
| CAS Number | 7803-51-2 |
| Appearance | Colorless gas with a disagreeable, fish-like or garlic-like odor. Highly toxic and pyrophoric (may ignite spontaneously in air at concentrations above 200 ppm). |
| Flash Point | Not applicable (pyrophoric gas, spontaneously flammable in air) |
| Boiling Point | -87.7C (-125.9F) |
| Vapor Density | 1.17 (heavier than air) |
| Water Reactivity | Reacts slowly with water to produce phosphorous acid and hydrogen; reaction accelerates with heat |
Fireground Response Guidance — UN 3525
Extinguishing Media
PPE Requirements
Use Level A fully encapsulating chemical protective clothing with positive-pressure SCBA for entry. Zone A toxic gas requires maximum respiratory and skin protection.
Isolation & Evacuation
First Actions for a UN 3525 Incident
- Call 911 and the emergency response number on the shipping paper, if available.
- Keep unauthorized personnel away and establish incident command.
- Stay upwind and avoid low or poorly ventilated areas unless monitoring shows they are safe.
- Treat the release as a life-threatening inhalation hazard until the gas is identified and monitored.
- Eliminate ignition sources if this can be done safely.
- Do not handle leaking cylinders, adsorbed-gas packages or damaged gas articles without proper training and PPE.
- Ventilate only after monitoring and only if properly trained and equipped.
- Use ERG Guide 173, shipping papers, markings and air monitoring to set isolation, evacuation and entry decisions.
📋 Copy & Share Field Card
UN 3525 — Phosphine, adsorbedUse 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.