UN 1064 — Methyl mercaptan
Placard: Toxic Gas. ERG Guide 117. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 1064 is Methyl mercaptan, a Class 2 toxic and flammable gas assigned to ERG Guide 117. It has a strong sulfur odor, but odor fatigue and toxicity make atmospheric monitoring and SCBA essential.
Hazard overview: UN 1064 combines toxic inhalation risk with flammable vapor behavior. Methyl mercaptan can form explosive mixtures with air, produce toxic fire gases and create dangerous exposure even when odor seems familiar or has become less noticeable.
Response guidance: For a UN 1064 incident, responders should confirm the product using shipping papers, SDS, cylinder markings and ERG Guide 117. Establish incident command, isolate the area, stay upwind, use atmospheric monitoring, control ignition sources when safe and require SCBA for suspected exposure areas.
Firefighter training notes: Training for UN 1064 should emphasize combined toxic and flammable gas risk, atmospheric monitoring, ignition control and SCBA use. Common errors include treating the release only as a fire problem, relying on odor, entering without monitoring and failing to control ignition sources.
Regulatory context: Methyl mercaptan is regulated as a hazardous material for transportation and emergency response purposes. Cylinder, workplace exposure, storage, reporting and environmental requirements may vary by product, quantity and jurisdiction. Responders should verify current requirements through shipping papers, SDS, cylinder markings, facility documents and applicable DOT, OSHA, EPA, NFPA, state or local authority guidance.
Storage & handling: Methyl mercaptan cylinders or containers should be stored secured, well ventilated and away from heat, ignition sources, oxidizers, incompatible gases and physical damage. Storage areas should control leaks, cylinder impact, unauthorized access and accumulation of gas in low or confined spaces.
UN 1064 Quick Details
Common Hazards of UN 1064
- TOXIC; may be fatal if inhaled or absorbed through skin.
- Flammable gas; may be ignited by heat, sparks or flames.
- May form explosive mixtures with air.
- Odor may be strong at low concentrations but should not be used as the only warning method.
- Contact with liquefied gas may cause frostbite or cold burns.
- Fire may produce irritating, corrosive and/or toxic gases.
- Vapors may spread along the ground and collect in low or confined areas.
Chemical Identity & Physical Properties
Colorless gas with a strong, unpleasant odor resembling rotten cabbage or garlic at low concentrations. Highly volatile and flammable. Shipped as a liquefied compressed gas.
| Also known as | MethanethiolMethyl sulfhydrateThiomethyl alcoholMercaptomethaneMethyl thioalcohol |
| CAS Number | 74-93-1 |
| Appearance | Colorless gas with a strong, unpleasant odor resembling rotten cabbage or garlic at low concentrations. Highly volatile and flammable. Shipped as a liquefied compressed gas. |
| Flash Point | -47C (-53F) |
| Boiling Point | 6C (43F) |
| Vapor Density | 1.66 (heavier than air) |
| Water Reactivity | Soluble in water with no significant reaction; may hydrolyze slowly in aqueous solutions |
Fireground Response Guidance — UN 1064
Extinguishing Media
PPE Requirements
Positive-pressure SCBA is essential for suspected toxic gas exposure. Chemical suit selection depends on the product, concentration and cylinder condition; respiratory protection, monitoring, exclusion zones and ignition control are the key safeguards.
Isolation & Evacuation
First Actions for a UN 1064 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.
- Do not touch damaged cylinders, tanks, valves or released material unless properly trained and equipped.
- Avoid breathing gas and eliminate ignition sources if it is safe to do so.
- Use atmospheric monitoring when available because toxic and flammable hazards may both be present.
- Ventilate closed spaces before entering, but only if properly trained, equipped and authorized by incident command.
- Isolate the spill or leak area for at least 100 meters (330 feet) in all directions.
- For highlighted materials, consult ERG Table 1 for Initial Isolation and Protective Action Distances.
- Use ERG Guide 117, shipping papers, SDS and incident command for evacuation and entry decisions.
📋 Copy & Share Field Card
UN 1064 — Methyl mercaptanUse 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.