Why does a CO₂ horn get so cold?

Liquid CO₂ stored at ~55 bar undergoes rapid adiabatic expansion as it exits the valve, cooling to approximately –78 °C and forming a mixture of CO₂ gas and dry-ice particles. The horn is in direct contact with this cryogenic stream. A frost-free horn insulates the operator's hand from this extreme cold.

What happens if I grab a bare metal horn during discharge?

Contact with a metal horn during CO₂ discharge causes almost instant frostbite—skin freezes to the metal surface within 2–3 seconds of sustained contact. This is why modern safety standards require non-metallic, frost-free horns on all CO₂ extinguishers.

Why is anti-static important on a CO₂ horn?

High-velocity CO₂ gas flowing through the horn generates triboelectric static charge. In environments with flammable vapours—server rooms near battery banks, solvent stores, fuel areas—a static spark could ignite the atmosphere. Anti-static horns dissipate charge safely through conductive additives in the polymer.

Can I replace just the horn or must I replace the entire hose assembly?

On most models, the horn press-fits onto the end of the high-pressure hose and can be replaced independently. Verify that the new horn diameter matches the hose end fitting. If the hose itself is damaged, replace both.

How do I check a horn for UV degradation?

Look for yellowing, surface chalking, or brittleness—press the bell gently; it should flex without cracking. Horns stored outdoors or on extinguishers exposed to direct sunlight degrade faster. If the horn feels rigid and discoloured, replace it.

Are all CO₂ horns the same size?

No. Horn bell diameter and connection type vary by extinguisher capacity: 2 kg units typically use a small rigid-mount horn, while 4.5 kg, 6.5 kg, and 9 kg units use progressively larger hose-mounted horns. Always order the size matched to the specific extinguisher model.

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CO₂ Extinguisher Discharge Horn – Frost-Free (Anti-Static)

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Product Details

MaterialGlass-reinforced nylon / polycarbonate / ABS

Frost ProtectionNon-conductive polymer construction

Anti-StaticCarbon-loaded / grounding path

Temperature Tolerance–80 °C to +70 °C

Connection TypesHose press-fit / rigid elbow (model-specific)

Compatible Extinguishers2 kg, 4.5 kg, 6.5 kg, 9 kg CO₂

Bell Diameter80–150 mm (size dependent)

StandardIS 15683 / EN 3-7

PackagingPack of 5 / 10 pcs

Extinguisher Replacement Parts

CO₂ Extinguisher Discharge Horn – Frost-Free (Anti-Static)

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Description

The discharge horn is the signature component of a CO₂ fire extinguisher and one of the most misunderstood. When liquid CO₂ stored at approximately 55–60 bar expands through the valve and into the horn, it undergoes a dramatic phase change: the sudden pressure drop causes adiabatic cooling, converting the liquid into a mixture of gaseous CO₂ and solid "dry ice" snow at approximately –78 °C. The horn's job is to direct this extremely cold discharge stream onto the fire while protecting the operator's hands from cryogenic contact.

Traditional horns were made from bare metal—effective at directing the gas but dangerously conductive of cold. Operators gripping a metal horn during a sustained discharge suffered frostbite injuries within seconds. Modern frost-free horns solve this with a non-conductive, non-metallic construction—typically glass-reinforced nylon, polycarbonate, or specially formulated ABS—that insulates the operator's hand from the cryogenic stream. Many designs include a moulded grip ring or handle positioned behind the horn bell, ensuring the operator's fingers never contact the discharge path.

The anti-static property is equally important. The high-velocity CO₂ gas flow generates significant static charge through triboelectric friction inside the horn. In environments with flammable vapours (the very situations where CO₂ extinguishers are commonly used), a static discharge from a non-anti-static horn could ignite the atmosphere. Anti-static horns incorporate conductive carbon particles or metallic grounding paths within the polymer matrix, dissipating charge safely to the extinguisher body and thence to ground.

Horn connections vary by manufacturer: the most common type press-fits onto a flexible high-pressure hose that swivels at the valve outlet. Some smaller CO₂ extinguishers (2 kg) mount the horn directly on the valve via a rigid elbow. Always match the horn connection type and diameter to the extinguisher model—forced fitting risks cracking the horn or damaging the hose coupling.

During servicing, the horn should be inspected for cracks, chips, UV degradation (yellowing/brittleness), and secure hose attachment. A cracked horn is a serious safety hazard—it can shatter during discharge, directing the cryogenic stream unpredictably and leaving the operator exposed. Replace any horn that shows visible damage, discolouration, or looseness at the connection.

Spare horns should be stored away from UV light and heat sources. They are lightweight and inexpensive; maintaining a stock of the three or four most common models (2 kg, 4.5 kg, 6.5 kg, and 9 kg CO₂ extinguisher horns) ensures fast turnaround during servicing.