UN 3255 — tert-Butyl hypochlorite
Placard: Spontaneously Combustible. ERG Guide 135. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 3255 tert-Butyl hypochlorite is assigned to ERG Guide 135 for initial emergency response. Colorless to pale yellow liquid with a pungent, irritating odor. Highly unstable and reactive at room temperature. Verify the exact product from shipping papers and SDS before selecting tactics.
Hazard overview: Primary hazards: a self-heating hazardous material that may ignite on contact with air or moisture. Flammable/combustible material. May ignite on contact with moist air or moisture.
Response guidance: For a UN 3255 incident, isolate the area, keep unauthorized personnel away, stay upwind/uphill and confirm the exact material from shipping papers and SDS. Avoid direct water or foam unless incident command confirms compatibility; use dry agents such as dry chemical, dry sand, lime or soda ash when specified. Follow ERG Guide 135 and local incident command procedures.
UN 3255 Quick Details
Common Hazards of UN 3255
- Flammable/combustible material.
- May ignite on contact with moist air or moisture.
- May burn rapidly with flare-burning effect.
- Some react vigorously or explosively on contact with water.
- Some may decompose explosively when heated or involved in a fire.
- May re-ignite after fire is extinguished.
- Runoff may create fire or explosion hazard.
- Containers may explode when heated.
Chemical Identity & Physical Properties
Colorless to pale yellow liquid with a pungent, irritating odor. Highly unstable and reactive at room temperature.
| Also known as | tert-Butyl hypochloriteHypochlorous acid tert-butyl ester2-Chloro-2-methylpropanet-Butyl hypochloriteTrimethylmethyl hypochlorite |
| CAS Number | 507-40-4 |
| Appearance | Colorless to pale yellow liquid with a pungent, irritating odor. Highly unstable and reactive at room temperature. |
| Flash Point | -9C (16F) |
| Boiling Point | 78-79C (172-174F) (decomposes) |
| Vapor Density | 3.8 (heavier than air) |
| Water Reactivity | Reacts with moisture and water, releasing hypochlorous acid and corrosive fumes. May ignite spontaneously in moist air. |
Fireground Response Guidance — UN 3255
Extinguishing Media
PPE Requirements
Level B minimum; SCBA required. Full chemical-resistant suit recommended due to flammability and corrosive vapor hazard.
Isolation & Evacuation
First Actions for a UN 3255 Incident
- CALL 911. Then call the emergency response telephone number on the shipping paper if available.
- Stay upwind, uphill and/or upstream.
- Keep unauthorized personnel away.
- Isolate spill or leak area in all directions for at least 50 meters (150 feet) for liquids and 25 meters (75 feet) for solids.
- For highlighted materials: see Table 1 - Initial Isolation and Protective Action Distances.
- For non-highlighted materials, increase the initial isolation distance in the downwind direction as needed.
📋 Copy & Share Field Card
UN 3255 — tert-Butyl hypochloriteUse 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.