☣️ UN 2646 • CLASS 6
Hexachlorocyclopentadiene
Placard: Toxic. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
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⚠️ This page is a quick-reference aid. For real incidents: stage upwind, isolate, deny entry, request Hazmat early, and consult the current ERG + SOP/SOG.
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Quick details
UN 2646
Class: 6
Placard type: Toxic
ERG: Guide 151 (check current ERG)
Isolation: ERG 151: isolate spill 50m all directions; initial evacuation 100m in all directions; if tank/rail car involved in fire, isolate 800m and consider evacuation 1600m downwind
Chemical & Response Details
| Also known as | HCCPDPerchlorocyclopentadieneC-56Hexachloro-1,3-cyclopentadiene |
| CAS Number | 77-47-4 |
| Appearance | Yellow to amber oily liquid with a pungent, acrid odor. Dense and readily volatilizes at room temperature. |
| Flash Point | Not flammable or combustible |
| Boiling Point | 239C (462F) |
| Vapor Density | 9.42 (much heavier than air) |
| Water Reactivity | Hydrolyzes slowly in water, producing toxic and corrosive gases |
| Extinguishing | Dry chemical, CO2, or foam may be used if necessary for surrounding fires |
| PPE | ⚠️ Level A minimum; SCBA and full chemical-protective suit required; avoid any skin contact |
| Isolation | ERG 151: isolate spill 50m all directions; initial evacuation 100m in all directions; if tank/rail car involved in fire, isolate 800m and consider evacuation 1600m downwind |
Chemical details are general reference only. Always verify with current SDS, ERG, and SOP/SOG.
Common hazards (high level)
- Highly toxic, may be fatal if inhaled, ingested or absorbed through skin.
- Avoid any skin contact.
- Fire may produce irritating, corrosive and/or toxic gases.
- Runoff from fire control or dilution water may be corrosive and/or toxic and cause environmental
- Non-combustible, substance itself does not burn but may decompose upon heating to produce corrosive
- Containers may explode when heated.
- Runoff may pollute waterways.
First actions (field-minded)
- CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper
- Keep unauthorized personnel away.
- Stay upwind, uphill and/or upstream.
- Isolate spill or leak area in all directions for at least 50 meters (150 feet) for liquids and at least 25 meters
- For highlighted materials: see Table 1 - Initial Isolation and Protective Action Distances.
- For non-highlighted materials: increase the immediate precautionary measure distance, in the downwind
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UN 2646 — Hexachlorocyclopentadiene HAZMAT RADIO NOTE — UN 2646
Product: Hexachlorocyclopentadiene
Class 6 / Toxic / ERG 151
PPE: Level A minimum; SCBA and full chemical-protective suit required; avoid any skin contact
ISOLATION: ERG 151: isolate spill 50m all directions; initial evacuation 100m in all directions; if tank/rail car involved in fire, isolate 800m and consider evacuation 1600m downwind
ACTION: Stage upwind · Isolate · Deny entry · Request HazmatRADIO
Use for: Quick radio or face-to-face size-up. Short, structured, field-ready.
=== IC HAZMAT BRIEFING ===
UN 2646 — Hexachlorocyclopentadiene
Class: 6 | Placard: Toxic | ERG Guide: 151
Appearance: Yellow to amber oily liquid with a pungent, acrid odor. Dense and readily volatilizes at room temperature.
Water Reactivity: Hydrolyzes slowly in water, producing toxic and corrosive gases
Extinguishing: Dry chemical, CO2, or foam may be used if necessary for surrounding fires
PPE: Level A minimum; SCBA and full chemical-protective suit required; avoid any skin contact
Isolation: ERG 151: isolate spill 50m all directions; initial evacuation 100m in all directions; if tank/rail car involved in fire, isolate 800m and consider evacuation 1600m downwind
— Key Hazards —
• Highly toxic, may be fatal if inhaled, ingested or absorbed through skin.
• Avoid any skin contact.
• Fire may produce irritating, corrosive and/or toxic gases.
— First Actions —
• CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper
• Keep unauthorized personnel away.
• Stay upwind, uphill and/or upstream.
• Isolate spill or leak area in all directions for at least 50 meters (150 feet) for liquids and at least 25 meters
SOURCE: allfirefighter.com/hazmat/un/2646 | Always use current ERG + SOP/SOGIC BRIEFING
Use for: Incident command briefing, staging area whiteboard, or pre-entry team brief. Full chemical + response details.
UN2646 Hexachlorocyclopentadiene Cls6 ERG151 | allfirefighter.com/hazmat/un/2646SMS / 160 CHAR
Use for: Quick text to command or incoming units. Fits in a single SMS. Includes link to full page.
⚠️ Quick-reference only. Always use current ERG + SOP/SOG for incident-specific actions. Page: https://allfirefighter.com/hazmat/un/2646
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FAQ
Highly toxic, may be fatal if inhaled, ingested or absorbed through skin. Avoid any skin contact. Fire may produce irritating, corrosive and/or toxic gases. Runoff from fire control or dilution water may be corrosive and/or toxic and cause environmental Non-combustible, substance itself does not burn but may decompose upon heating to produce corrosive Containers may explode when heated. Runoff may pollute waterways.
CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper Keep unauthorized personnel away. Stay upwind, uphill and/or upstream.
Level A minimum; SCBA and full chemical-protective suit required; avoid any skin contact
No. This is a training/quick-reference aid only. Always consult the current ERG Guide 151 and your department SOP/SOG for incident-specific protective actions.
Sources (high level): DOT/PHMSA marking & class concepts + ERG usage principles. This page does not reproduce ERG guide text—always consult the current ERG for incident-specific protective actions.