UN 1642 — Mercury oxycyanide, desensitized
Placard: Toxic. ERG Guide 151. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
UN 1642 is Mercury oxycyanide, desensitized, a highly toxic cyanide and mercury material assigned to ERG Guide 151. Acids, moisture or heat can release hydrogen cyanide, while mercury contamination can persist in runoff and equipment.
Hazard overview: UN 1642 presents cyanide poisoning, hydrogen cyanide gas and mercury contamination hazards. Avoid acid contact, control runoff, monitor for HCN where possible and do not rely on odor as a warning.
Response guidance: For a UN 1642 incident, responders should verify the product with shipping papers, package markings, SDS and ERG Guide 151. Establish incident command, isolate the area, stay upwind, prevent dust or vapor exposure, control runoff and choose entry or cleanup actions based on monitoring, SDS and local SOP.
Firefighter training notes: Training for UN 1642 should emphasize hydrogen cyanide generation, acid/moisture incompatibility, mercury contamination, air monitoring, SCBA use, decontamination and medical coordination. Use ERG 151, SDS and local SOP.
Regulatory context: Mercury oxycyanide, desensitized is regulated as a toxic cyanide and mercury hazardous material. Transportation, exposure, spill reporting, waste handling and environmental requirements may be strict and jurisdiction-dependent. Verify current requirements through shipping papers, SDS, facility documents and applicable DOT, OSHA, EPA, NFPA, state or local authority guidance.
Storage & handling: Mercury oxycyanide, desensitized should be stored in tightly closed compatible containers in a secure, dry, well-ventilated toxic-material area away from acids, moisture contamination, oxidizers, heat and unauthorized access. Storage should include cyanide emergency planning and mercury-contaminated runoff control appropriate to the SDS.
UN 1642 Quick Details
Common Hazards of UN 1642
- HIGHLY TOXIC mercury cyanide material; inhalation, ingestion or skin contact may be fatal.
- Acids, moisture or heat may release hydrogen cyanide gas.
- Hydrogen cyanide can be flammable and rapidly dangerous in low or poorly ventilated areas.
- Mercury contamination may remain in dust, solution, runoff, clothing or equipment.
- Fire may produce hydrogen cyanide, mercury fumes and other toxic gases.
- Containers may rupture or fail when heated.
- Odor is not a reliable warning for hydrogen cyanide exposure.
Chemical Identity & Physical Properties
White to yellowish crystalline solid or powder. Odorless or faint characteristic odor. Stable at room temperature when desensitized.
| Also known as | Mercury(II) oxycyanideMercuric oxycyanideMercury oxide cyanideOxycyanomercury |
| CAS Number | 1335-31-5 |
| Appearance | White to yellowish crystalline solid or powder. Odorless or faint characteristic odor. Stable at room temperature when desensitized. |
| Flash Point | Not applicable (non-flammable solid) |
| Boiling Point | Decomposes before boiling at elevated temperatures |
| Vapor Density | Not applicable (solid) |
| Water Reactivity | Slightly soluble in water; hydrolyzes slowly releasing toxic mercury and cyanide compounds |
Fireground Response Guidance — UN 1642
Extinguishing Media
PPE Requirements
Use positive-pressure SCBA and chemical protective clothing selected by hazmat specialists for cyanide dust, solution, vapor or fire exposure. Level A may be needed for close entry or unknown hydrogen cyanide concentrations; decontamination should address both cyanide and mercury contamination.
Isolation & Evacuation
First Actions for a UN 1642 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 or mist and avoid all skin or eye contact.
- Avoid acids, water contamination or incompatible cleanup materials contacting cyanide product unless incident command confirms a safe control method.
- Do not touch or walk through spilled material unless properly trained and wearing appropriate protective equipment.
- Avoid creating dust clouds or spreading contaminated powder, solution, runoff or debris.
- Monitor for hydrogen cyanide where available; odor is not a reliable warning.
- 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 dust, vapor, fire involvement or unknown concentration is present.
- Use ERG Guide 151, shipping papers, SDS, air monitoring and incident command for protective actions.
📋 Copy & Share Field Card
UN 1642 — Mercury oxycyanide, desensitizedUse 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.