UN 1859 — Silicon tetrafluoride, compressed
Placard: Toxic Gas. ERG Guide 125. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 1859 is Silicon tetrafluoride, compressed, a toxic corrosive compressed gas assigned to ERG Guide 125. Moisture can form hydrogen fluoride and silicon-containing corrosive fumes.
Hazard overview: UN 1859 presents toxic inhalation, corrosive fluoride fume, heavier-than-air gas, frostbite and cylinder rupture hazards. Avoid low areas and follow ERG 125 and Table 1 where applicable.
Response guidance: For a UN 1859 incident, responders should verify the product with shipping papers, package markings, SDS and ERG Guide 125. Establish incident command, isolate the area, stay upwind, control ignition or incompatibility hazards, prevent runoff or vapor spread and choose entry/fire-control actions based on monitoring, SDS and local SOP.
Firefighter training notes: Training for UN 1859 should emphasize heavier-than-air gas behavior, cylinder rupture/rocket hazard, oxygen displacement, frostbite risk, vapor monitoring and downwind control. Use ERG 125, SDS and local SOP.
Regulatory context: Silicon tetrafluoride, compressed is regulated as a hazardous material for transportation and emergency response purposes. Transportation, workplace exposure, spill reporting, waste handling, storage and environmental requirements may vary by formulation, concentration, quantity and jurisdiction. Verify current requirements through shipping papers, SDS, facility documents and applicable DOT, OSHA, EPA, NFPA, state or local authority guidance.
Storage & handling: Silicon tetrafluoride, compressed cylinders should be secured upright in a cool, ventilated area away from heat, flames, physical damage and incompatible materials. Toxic or corrosive gas storage should include leak detection and emergency ventilation where required by SDS and local code.
UN 1859 Quick Details
Common Hazards of UN 1859
- TOXIC and CORROSIVE compressed gas; inhalation may be fatal or cause severe respiratory injury.
- Reacts with moisture to form hydrogen fluoride and silicic acid/silica-type fumes.
- Gas is heavier than air and may collect in low or confined areas.
- Contact with gas or liquefied gas may cause chemical burns, severe injury and/or frostbite.
- Fire or heating may produce irritating, corrosive and/or toxic gases.
- Water contact may increase corrosive fluoride contamination.
- Cylinders or containers may rupture or rocket when heated.
Chemical Identity & Physical Properties
Colorless gas with a pungent, suffocating odor. Fumes strongly in moist air forming white clouds of silica and hydrofluoric acid.
| Also known as | Silicon tetrafluorideTetrafluorosilaneSiF4Silicon fluoride |
| CAS Number | 7783-61-1 |
| Appearance | Colorless gas with a pungent, suffocating odor. Fumes strongly in moist air forming white clouds of silica and hydrofluoric acid. |
| Flash Point | Not applicable (non-flammable gas) |
| Boiling Point | -86C (-123F) |
| Vapor Density | 3.6 (heavier than air) |
| Water Reactivity | Reacts violently with water producing highly toxic and corrosive hydrofluoric acid and silicic acid fumes |
Fireground Response Guidance — UN 1859
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA and chemical protective clothing for gas, liquid, fire or confined-space exposure. Level A may be needed for close entry or unknown concentrations because toxic corrosive fluoride fumes are possible.
Isolation & Evacuation
First Actions for a UN 1859 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 vapors, fumes, dust, mist, smoke or gas and avoid skin or eye contact.
- Avoid low areas, basements, trenches and confined spaces where heavier-than-air gas may collect.
- Avoid water contact with gas plume or liquid release unless directed by incident command because fluoride contamination may increase.
- Do not touch or walk through spilled material unless properly trained and wearing appropriate protective equipment.
- Ventilate closed spaces before entering, but only if properly trained, equipped, monitored and authorized by incident command.
- Isolate the spill or leak area and expand the perimeter if vapor, dust, fire involvement, gas accumulation or unknown concentration is present.
- Use ERG Guide 125, shipping papers, SDS, air monitoring and incident command for protective actions.
📋 Copy & Share Field Card
UN 1859 — Silicon tetrafluoride, compressedUse 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.