UN 1017 — Chlorine
Placard: Toxic Gas. ERG Guide 124. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
Chlorine is a toxic and corrosive gas, classified as a DOT Class 2 substance. It is widely used in industrial processes, such as water treatment and disinfection, and is also used as a bleach. First responders may encounter chlorine in various settings, including industrial facilities, transportation accidents, and storage facilities. The scale of production and transport of chlorine is significant, with millions of tons being produced and transported each year. Chlorine is also known by its synonyms, including Molecular chlorine, Cl2, and Bertholite. The chemical identity of chlorine is characterized by its CAS number, 7782-50-5.
Hazard overview: Chlorine is toxic and corrosive, and may be fatal if inhaled or absorbed through the skin. It will produce irritating, corrosive, and/or toxic gases when burned, and contact with gas or liquefied gas may cause burns, severe injury, and/or frostbite. The vapor density of chlorine is 2.5, which is heavier than air, and it has a pungent, irritating odor detectable at very low concentrations. The LC50 of chlorine is not well-established, but it is known to be highly toxic and may cause severe injury or death if inhaled or absorbed through the skin. In a worst-case scenario, chlorine may react with water to form hypochlorous and hydrochloric acids, resulting in a corrosive solution.
Response guidance: In the event of a chlorine spill or leak, first responders should isolate the area to a distance of 150m in all directions as an immediate precaution, and evacuate the area to a distance of 800m downwind if a large spill occurs. The correct suppression agent for chlorine is not applicable for extinguishment, but water spray may be used to reduce vapors. Decontamination procedures should be followed, and CHEMTREC should be contacted for assistance. It is also important to note that chlorine may react with other substances, such as water, to form corrosive solutions.
Firefighter training notes: First responders should be trained to recognize the hazards of chlorine, including its toxicity and corrosive potential. They should also be trained to use the correct PPE and suppression agents, and to follow decontamination procedures. A common tactical error when responding to a chlorine incident is to underestimate the potential for toxic exposure, and to fail to isolate the area sufficiently. ICS position needs and mutual aid criteria should also be considered when responding to a chlorine incident.
Regulatory context: Chlorine is classified as a DOT Class 2 substance, and is subject to the regulations of the Department of Transportation. The OSHA PEL for chlorine is 0.5 ppm, and it is listed on the CERCLA list, which requires special handling and reporting procedures.
Storage & handling: Chlorine should be stored in a well-ventilated area, away from heat sources and ignition sources. The temperature limit for chlorine storage is not well-established, but it should be kept away from incompatible materials, such as water and ammonia. The container type for chlorine storage is typically a cylinder, and it should be handled with caution to prevent accidents and injuries.
UN 1017 Quick Details
Common Hazards of UN 1017
- TOXIC and/or CORROSIVE; may be fatal if inhaled or absorbed through skin.
- Fire will produce irritating, corrosive and/or toxic gases.
- Contact with gas or liquefied gas may cause burns, severe injury and/or frostbite.
- Runoff from fire control or dilution water may cause environmental contamination.
- Substance does not burn but will support combustion.
- Vapors from liquefied gas are initially heavier than air and spread along ground.
- These are strong oxidizers and will react vigorously or explosively with many materials including fuels.
- May ignite combustibles (wood, paper, oil, clothing, etc.).
Chemical Identity & Physical Properties
Chlorine is a greenish-yellow gas with a pungent, irritating odor detectable at very low concentrations. It is shipped as a liquefied compressed gas, and has a boiling point of -34C. The vapor density of chlorine is 2.5, which is heavier than air, and it reacts with water to form hypochlorous and hydrochloric acids.
| Also known as | Molecular chlorineCl2BertholiteDichlorine |
| CAS Number | 7782-50-5 |
| Appearance | Greenish-yellow gas with a pungent, irritating odor detectable at very low concentrations. Shipped as a liquefied compressed gas. |
| Flash Point | Not applicable (non-flammable gas) |
| Boiling Point | -34C (-29F) |
| Vapor Density | 2.5 (heavier than air) |
| Water Reactivity | Reacts with water to form hypochlorous and hydrochloric acids; corrosive solution |
Fireground Response Guidance — UN 1017
Extinguishing Media
PPE Requirements
The recommended PPE level for chlorine is Level A required for vapor concentrations, with positive pressure SCBA and chemical-resistant suit mandatory. It is also important to avoid all ignition sources, and to use caution when handling chlorine to prevent accidents and injuries. The use of SCBA and chemical-resistant suits is critical to prevent exposure to chlorine, which can cause severe injury or death.
Isolation & Evacuation
First Actions for a UN 1017 Incident
- Keep unauthorized personnel away.
- Stay upwind, uphill and/or upstream.
- Ventilate closed spaces before entering, but only if properly trained and equipped.
- Isolate spill or leak area for at least 100 meters (330 feet) in all directions.
- See Table 1 - Initial Isolation and Protective Action Distances.
📋 Copy & Share Field Card
UN 1017 — ChlorineUse 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.