UN 2834 — Phosphorous acid
Placard: Corrosive. ERG Guide 154. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 2834 is Phosphorous acid, a corrosive acidic solid assigned to ERG Guide 154. Dust, heat on dissolution and acidic runoff require control.
Hazard overview: CORROSIVE acidic solid; dust or solution can burn eyes, skin and respiratory tissue. Dissolves in water with heat release, forming acidic solution. Non-combustible, but heating can produce phosphorus oxides and irritating acidic fumes.
Response guidance: For UN 2834, isolate the area, avoid skin contact and use SCBA where dust, vapor, mist or fire is present. Contain corrosive/toxic runoff and verify controls with SDS and ERG 154.
Firefighter training notes: Training for UN 2834 should emphasize exposure routes, SCBA use, vapor/dust monitoring, fire behavior, decontamination, runoff containment and SDS verification. Use ERG 154, SDS and local SOP.
Regulatory context: Phosphorous acid is regulated as a hazardous material for transport and emergency response. Storage, exposure, spill reporting, waste and fire-code duties depend on quantity, concentration and jurisdiction; verify shipping papers, SDS and local authority requirements.
Storage & handling: Phosphorous acid should be stored in tightly closed compatible containers with ventilation, secondary containment, restricted access and SDS-based segregation from incompatible materials.
UN 2834 Quick Details
Common Hazards of UN 2834
- CORROSIVE acidic solid; dust or solution can burn eyes, skin and respiratory tissue.
- Dissolves in water with heat release, forming acidic solution.
- Non-combustible, but heating can produce phosphorus oxides and irritating acidic fumes.
- Contact with metals may generate flammable hydrogen gas under acidic conditions.
- Runoff may be acidic, corrosive and harmful to waterways.
- Dust can irritate lungs and contaminate clothing or tools.
- Containers may fail when heated or exposed to moisture.
Chemical Identity & Physical Properties
White or yellowish crystalline solid or powder. Odorless or slight garlic-like odor. Hygroscopic, absorbs moisture from air.
| Also known as | Phosphonic acidOrthophosphorous acidTrihydroxyphosphine oxide |
| CAS Number | 10294-56-1 |
| Appearance | White or yellowish crystalline solid or powder. Odorless or slight garlic-like odor. Hygroscopic, absorbs moisture from air. |
| Flash Point | Not applicable (non-combustible solid) |
| Boiling Point | Decomposes at 200C (392F) before boiling |
| Vapor Density | Not applicable (solid at room temperature) |
| Water Reactivity | Dissolves in water releasing heat; forms acidic solution; no violent reaction |
Fireground Response Guidance — UN 2834
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA for vapor, dust, mist, fire or confined-space exposure. Wear chemical-resistant gloves, boots, eye/face protection and protective clothing.
Isolation & Evacuation
First Actions for a UN 2834 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.
- 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 154, SDS, shipping papers and monitoring to set isolation, evacuation and entry decisions.
📋 Copy & Share Field Card
UN 2834 — Phosphorous acidUse 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.