UN 1717 — Acetyl chloride
Placard: Flammable. ERG Guide 155. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
Acetyl chloride, UN 1717, is a highly flammable and toxic substance classified as a DOT Class 3 material. It is widely used in various industrial applications, including the manufacture of pharmaceuticals, dyes, and pesticides. First responders may encounter acetyl chloride during transportation accidents or industrial spills. The scale of production and transportation of acetyl chloride is significant, with thousands of tons being moved annually. As a result, it is essential for emergency responders to be aware of the hazards associated with this substance and take appropriate precautions. Acetyl chloride is a colorless to slightly yellow fuming liquid with a pungent, irritating odor.
Hazard overview: Acetyl chloride is highly flammable and toxic, posing a significant threat to human health and the environment. The substance can be easily ignited by heat, sparks, or flames, and vapors can form explosive mixtures with air. The vapor density of acetyl chloride is 2.7, which is heavier than air, making it a significant hazard in enclosed spaces. The LC50 value for acetyl chloride is not available, but it is known to be highly toxic. In the worst-case scenario, acetyl chloride can cause severe burns to skin and eyes, and prolonged exposure can lead to respiratory problems.
Response guidance: In case of an acetyl chloride spill, it is essential to isolate the area 50m in all directions and evacuate the immediate area if fire involves containers. First responders should wear Level B protective gear, including a chemical-resistant suit for splash protection, and a full face SCBA. The correct suppression agent for acetyl chloride is dry chemical, CO2, or dry sand, and alcohol-resistant foam may be used at a distance. No water jets should be used. Decontamination is critical, and CHEMTREC should be contacted immediately in case of a spill. It is also essential to ventilate closed spaces before entering and to stay upwind, uphill, and/or upstream of the spill.
Firefighter training notes: First responders should be trained to handle acetyl chloride spills and leaks. A critical competency requirement is the ability to identify the substance and take appropriate precautions. A known tactical error for this chemical class is the use of water directly on the spill, which can increase the risk of explosion and worsen the situation. ICS position needs include a hazardous materials team leader and a safety officer, and mutual aid criteria include the availability of Level B protective gear and CHEMTREC contact information.
Regulatory context: Acetyl chloride is classified as a DOT Class 3 material, and it is subject to the regulations of the Pipeline and Hazardous Materials Safety Administration (PHMSA). The OSHA PEL for acetyl chloride is not established, but the substance is listed on the CERCLA list of hazardous substances. The packing group for acetyl chloride is not available, but it is considered a highly flammable and toxic substance.
Storage & handling: Acetyl chloride should be stored in a cool, dry, well-ventilated area away from incompatible materials such as water and ignition sources. The temperature limit for storage is 20C (68F), and the substance should be kept away from heat sources and ignition sources. The top three incompatible materials for acetyl chloride are water, aluminum, and magnesium, and the ventilation standard for storage is a well-ventilated area with a minimum of 10 air changes per hour.
UN 1717 Quick Details
Common Hazards of UN 1717
- HIGHLY FLAMMABLE: Will be easily ignited by heat, sparks or flames.
- Vapors form explosive mixtures with air: indoors, outdoors and sewers explosion hazards.
- Most vapors are heavier than air. They will spread along the ground and collect in low or confined areas
- Vapors may travel to source of ignition and flash back.
- Those substances designated with a (P) may polymerize explosively when heated or involved in a fire.
- Substance will react with water (some violently) releasing flammable, toxic or corrosive gases and runoff.
- Corrosives in contact with metals may evolve flammable hydrogen gas.
- Containers may explode when heated or if contaminated with water.
Chemical Identity & Physical Properties
Acetyl chloride is a colorless to slightly yellow fuming liquid with a pungent, irritating odor. It has a boiling point of 51C (124F) and a vapor pressure of 100 mmHg at 20C. The specific gravity of acetyl chloride is 1.1, making it slightly denser than water. The substance reacts violently with water, producing heat, corrosive acetic acid, and HCl fumes.
| Also known as | Ethanoyl chlorideAcetic acid chlorideAcetic chloride |
| CAS Number | 75-36-5 |
| Appearance | Colorless to slightly yellow fuming liquid with a pungent, irritating odor. Fumes in moist air due to reaction with water vapor. |
| Flash Point | 4C (40F) |
| Boiling Point | 51C (124F) |
| Vapor Density | 2.7 (heavier than air) |
| Water Reactivity | Reacts violently with water producing heat, corrosive acetic acid and HCl fumes. Do not use water directly on material. |
Fireground Response Guidance — UN 1717
Extinguishing Media
PPE Requirements
First responders should wear Level B protective gear, including a chemical-resistant suit for splash protection, and a full face SCBA. The rationale for this level of protection is the high flammability and toxicity of acetyl chloride and the potential for skin and eye irritation. The SCBA is necessary to prevent inhalation of the toxic vapors, while the chemical-resistant suit provides protection against skin contact.
Isolation & Evacuation
First Actions for a UN 1717 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 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
📋 Copy & Share Field Card
UN 1717 — Acetyl chlorideUse 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.