UN 3023 — 2-Methyl-2-heptanethiol
Placard: Toxic. ERG Guide 131. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
2-Methyl-2-heptanethiol (UN 3023) is a toxic, flammable mercaptan liquid with a strong odor. First response priorities are vapor control, ignition control and exposure prevention.
Hazard overview: UN 3023 presents both toxic vapor exposure and flammable liquid hazards. Vapors may travel along the ground, ignite at a distance and produce irritating sulfur-containing smoke in a fire.
Response guidance: Isolate the area, remove ignition sources and keep responders upwind. Use alcohol-resistant foam, dry chemical or CO2 for fire control, with water spray for cooling containers only. Prevent runoff and avoid direct skin contact.
Firefighter training notes: Train crews not to rely on odor as a safe indicator and to control ignition sources before approaching mercaptan spills.
Regulatory context: UN 3023 is regulated as a toxic flammable liquid for transport; ERG 131 and the SDS should guide initial action.
Storage & handling: Store away from ignition sources, oxidizers and incompatible materials in tightly closed containers with ventilation and spill containment.
UN 3023 Quick Details
Common Hazards of UN 3023
- Toxic flammable liquid; inhalation, ingestion or skin absorption may cause serious injury.
- Vapors are heavier than air and may collect in low or confined spaces.
- Mercaptan odor is strong but odor should not be used to judge safe exposure levels.
- Vapors may form explosive mixtures with air and flash back to the source.
- Fire produces irritating sulfur oxides and other toxic gases.
- Liquid is insoluble in water and can spread on surfaces or runoff.
- Containers may rupture when heated.
Chemical Identity & Physical Properties
Colorless to pale yellow liquid with a strong, offensive mercaptan (skunk-like) odor. Liquid at room temperature. It is heavier than water-insoluble behavior should be confirmed at the scene from SDS data.
| Also known as | tert-Octanethiol1,1-Dimethylhexanethiol2-Methylheptane-2-thioltert-Octyl mercaptan |
| CAS Number | 1639-09-4 |
| Appearance | Colorless to pale yellow liquid with a strong, offensive mercaptan (skunk-like) odor. Liquid at room temperature. |
| Flash Point | 43°C (109°F) |
| Boiling Point | 155-157°C (311-315°F) |
| Vapor Density | 5.0 (heavier than air) |
| Water Reactivity | No significant reaction with water; insoluble in water |
Fireground Response Guidance — UN 3023
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA and chemical-resistant clothing. Select gloves and suit material from the SDS because mercaptan liquids may permeate some materials.
Isolation & Evacuation
First Actions for a UN 3023 Incident
- Call 911 and the emergency response number on the shipping paper, if available.
- Eliminate ignition sources; use non-sparking tools and control traffic around the spill.
- Keep unauthorized personnel away and stay upwind, uphill and upstream.
- Avoid breathing vapors and prevent liquid contact with skin, eyes and clothing.
- Do not enter low areas, drains or confined spaces unless trained and equipped.
- Use ERG 131, SDS, shipping papers and monitoring to set isolation and evacuation distances.
- Contain runoff only if it can be done safely with proper PPE.
📋 Copy & Share Field Card
UN 3023 — 2-Methyl-2-heptanethiolUse 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.