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    Extinguishers: Test CO2 Extinguisher Hoses to Ensure Safety

    By Mark Conroy


    The friction of carbon dioxide being released from a CO2 extinguisher generates static electricity. For safety reasons, a safe electrical bond must be created between the CO2 cylinder and the discharge point. That electrical bond is either the metal discharge tube (small extinguishers) or the extinguisher hose (larger extinguishers). In order to create an electrical bond and equalize the potential electrical energy, a CO2 extinguisher hose has a continuous metal wire braid inside the rubber hose cover. That continuous braid creates a circuit for the electricity to flow along the braid in the hose, rather than through the operator’s body. A break in the wire braid creates a potentially dangerous situation for an extinguisher operator. Without the continuity of the metal braid, the flow of the electrical charge can travel through the operator’s body. The electrical shock can range from mild discomfort in the hands of the operator to an electrical charge that can travel from one hand to the other and across the heart, which could be dangerous for a person with a heart condition. That’s why the metal braid is required to be tested annually. Here’s what you need to know regarding the required testing.


    Test Requirement and Procedure

    NFPA 10, Standard for Portable Fire Extinguishers requires that a conductivity test be performed on the hose assembly of the CO2 extinguisher [10: 7.4]. To perform the test, the hose must be removed from the extinguisher and placed on a nonconductive bench (e.g. wooden). A technician needs a CO2 hose continuity tester to conduct the test. There are two types of testers. CHT is a tester with a metal wire and alligator clip. The more modern NCHT tester has no wire or clip. To use the NCHT tester, the technician holds a hose coupling in one hand and with the other hand touches the probe on the tester to the coupling at the other end of the hose. The red LED light will illuminate if there is conductivity. When the light glows brightly, the hose passes the test. Hoses that fail the test are replaced.

    NCHT CO2 Hose Continuity Testers

    Test Record

    Hoses that pass the test are required to have a label attached to the hose that serves as a test record. The conductivity test label SSPCTL is most often used for this purpose.


    Replacement CO2 Extinguisher Hoses

    Hand Portable Wheeled
    P/N 32A 32B 36A 36B 15FF 40FF
    Hose Length 32 Inches 32 Inches 36 Inches 36 Inches 15 Feet 40 Feet
    Female Couplings ¼″ x ¼″ ¼″ x ⅜″ ¼″ x ¼″ ¼″ x ⅜″ ½″ x ½″ ½″ x ½″

    Testing CO2 extinguisher hoses annually and replacing defective ones ensures safety for extinguisher operators. Your knowledge of these testing requirements will help ensure your customer’s CO2 extinguishers will remain safe if they are ever needed for a fire emergency.



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    Mark Conroy is an engineer in our Boston, MA office. © 2019 Brooks Equipment.

    Disclaimer: The opinions expressed in the above Tech Series article are the author’s only and provide limited information. Although the information is believed to be reliable, Brooks Equipment Company, LLC expressly disclaims any warranty with respect to the information and any liability for errors or omissions. The user of this article or the product(s) is responsible for verifying the information’s accuracy from all available sources, including the product manufacturer. The authority having jurisdiction should be contacted for code interpretations.