UN 1050 — Hydrogen chloride, anhydrous
Placard: Toxic Gas. ERG Guide 125. Training/quick-reference only — use current ERG + SOP/SOG for incident-specific actions.
Hydrogen chloride, anhydrous, is a colorless to slightly yellow gas with a pungent, irritating odor, widely used in various industrial processes, including the production of hydrochloric acid, vinyl chloride, and other chemicals. As a DOT class 2 gas, it is highly toxic and corrosive, posing significant risks to first responders and the general public. The scale of production and transport of hydrogen chloride is substantial, with millions of tons being manufactured and shipped annually. First responders may encounter hydrogen chloride in various scenarios, including transportation accidents, industrial leaks, and fires. The gas is highly soluble in water, generating significant heat and forming corrosive hydrochloric acid solutions. Hydrogen chloride is also known as hydrochloric acid gas, muriatic acid gas, or HCl, with a CAS number of 7647-01-0.
Hazard overview: Hydrogen chloride is a toxic and corrosive gas that can cause severe irritation and damage to the skin, eyes, and respiratory system. Its vapors are extremely irritating and corrosive, making it a highly hazardous substance.
Response guidance: In the event of a hydrogen chloride release, first responders should isolate the area with a minimum distance of 100m in all directions, using water spray to absorb the gas and reduce the vapor cloud. Evacuation zones should be established, with a protective action distance of 0.6 km daytime or 1.7 km nighttime for large spills. The correct suppression agent is not applicable for fire control, but water spray can be used to disperse vapors or protect exposures. Decontamination procedures should be followed, and CHEMTREC should be contacted in case of a large-scale release or uncertainty about the response. First responders should stay upwind, uphill, and/or upstream, keeping unauthorized personnel away from the affected area.
Firefighter training notes: First responders should be trained to recognize the hazards of hydrogen chloride, including its toxic and corrosive properties, and be competent in responding to large-scale releases. A known tactical error for this chemical class is underestimating the distance the gas can travel, leading to inadequate evacuation zones. ICS position needs include a hazardous materials team, and mutual aid criteria should be established for large-scale releases. First responders should be aware of the gas's ability to dissolve in water, generating significant heat and forming corrosive hydrochloric acid solutions.
Regulatory context: Hydrogen chloride is classified as a DOT class 2 gas, with a packing group not established due to its highly corrosive nature. The OSHA PEL for hydrogen chloride is 5 ppm (7 mg/m3) as an 8-hour TWA, and the gas is not listed on the CERCLA list. However, it is highly toxic and corrosive, requiring special handling and response procedures.
Storage & handling: Hydrogen chloride should be stored in a well-ventilated area, away from incompatible materials such as water, ammonia, and alkali metals. The temperature limit for storage is not established due to its highly corrosive nature, but the gas should be kept away from heat sources and ignition sources. The container type should be compatible with the gas, and ventilation standards should be followed to prevent the accumulation of hydrogen chloride vapors.
UN 1050 Quick Details
Common Hazards of UN 1050
- TOXIC and/or CORROSIVE; may be fatal if inhaled, ingested or absorbed through skin.
- Vapors are extremely irritating and corrosive.
- Contact with gas or liquefied gas may cause burns, severe injury and/or frostbite.
- Fire will produce irritating, corrosive and/or toxic gases.
- Runoff from fire control or dilution water may cause environmental contamination.
- Some may burn but none ignite readily.
- Vapors from liquefied gas are initially heavier than air and spread along ground.
- Some of these materials may react violently with water.
Chemical Identity & Physical Properties
Hydrogen chloride is a colorless to slightly yellow gas with a pungent, irritating odor, fuming heavily in moist air to form a white corrosive mist. The gas has a boiling point of -85C (-121F) and a vapor pressure not established due to its highly corrosive nature. The specific gravity of hydrogen chloride is not applicable due to its gaseous state, but it is heavier than air, with a vapor density of 1.3.
| Also known as | Hydrochloric acid gasMuriatic acid gasHClAnhydrous hydrochloric acidChlorohydric acid |
| CAS Number | 7647-01-0 |
| Appearance | Colorless to slightly yellow gas with a pungent, irritating odor. Fumes heavily in moist air forming white corrosive mist. |
| Flash Point | Not applicable (non-flammable gas) |
| Boiling Point | -85C (-121F) |
| Vapor Density | 1.3 (heavier than air) |
| Water Reactivity | Dissolves readily in water generating significant heat and forming corrosive hydrochloric acid solution |
Fireground Response Guidance — UN 1050
Extinguishing Media
PPE Requirements
First responders should wear a minimum of Level B personal protective equipment, including a full-face SCBA and chemical-resistant suit, when responding to a hydrogen chloride release. The SCBA type should be compatible with the gas, and the suit material should be resistant to hydrogen chloride. Gloves should be worn to prevent skin contact, and the rationale for each item is to prevent exposure to the highly toxic and corrosive gas. Upgrade to Level A PPE is required for high concentrations or confined space operations.
Isolation & Evacuation
First Actions for a UN 1050 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.
- 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 1050 — Hydrogen chloride, anhydrousUse 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.