Koorsen Fire & Security — Hazardous Materials Safety Interpretation

Page 11200 New Jersey Avenue, SE Washington, DC 20590 U.S. Department of Transportation Pipeline and Hazardous Materials Safety Administration July 28, 2026 Mr. Brick Keltner Corporate Shop Trainer Koorsen Fire & Security 2820 N. Webster Ave Indianapolis, IN 46219-1013 Reference No. 26-0050 Dear Mr. Keltner: This is in response to your April 27, 2026 letter requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to the requalification of Department of Transportation (DOT) specification 4BA and 4BW cylinders used in fire suppression systems that are installed in restaurants, kitchens, or paint booths. We have paraphrased and answered your questions as follows: Q1. Does a DOT 4BA or 4BW fire suppression cylinder that has a water capacity over 5.44 kg (12 pounds) meet the definition of a “fire extinguisher?” A1. Yes. A DOT 4BA or 4BW cylinder used in a suppression system meets the definition of a fire extinguisher under § 173.309, provided it is charged with either a compressed gas and an extinguishing agent, or a gas which comprises the sole fire extinguishing agent. See § 173.309(a)(1)-(5). Note that this definition does not include cylinders pressurized with a gas solely for the purpose of expelling a separately stored extinguishing agent in the fire suppression system. Q2. If the answer to Q1 is yes, is a DOT 4BA or 4BW fire suppression cylinder that has a water capacity over 5.44 kg (12 pounds) required to be tested 12 years after the original test date and at 7-year intervals thereafter? A2. Yes. Under § 180.209(j)(1)(ii), a DOT 4BA or 4BW cylinder with a water capacity over 5.44 kg (12 pounds) that meets the definition of a fire extinguisher in § 173.309 must be requalified 12 years after the original test date. If the proof pressure test method is used, the requalification must be performed 12 years after the original test date, and at 7-year intervals thereafter. For the water-jacket or direct expansion test, the requalification must be performed by the end of 12 years after the original test date and at 12-year intervals#

Page 2thereafter. Alternatively, the cylinder may be requalified in accordance with any of the other eligible requalification periods that the cylinder meets in § 180.209. Q3. Does a DOT 4BA or 4BW fire suppression cylinder that has a water capacity over 5.44 kg (12 pounds) installed on a mobile food truck or trailer meet the requirement to be tested 12 years after the original test date and at 7-year intervals thereafter? A3. Yes. The HMR classification of a cylinder as a fire extinguisher for transportation purposes under § 173.309 is based on its configuration and function (i.e., being installed as part of a fire suppression system). Therefore, a qualifying cylinder installed on a mobile food truck or trailer may follow the same 12-year initial and 7-year or 12-year subsequent requalification intervals, depending on requalification test method under § 180.209(j), as a system installed in a fixed building or any other configuration it may be in when not in transportation. Q4. Do the provisions applicable to fire suppression systems apply to both wet and dry chemical suppression systems (e.g., wet chemical in kitchens/restaurants and dry chemical in paint booths)? A4. Yes. The definition of a fire extinguisher in the introductory text to § 173.309 does not differentiate between the types of chemical agents used, provided the cylinder is charged with a compressed gas and an extinguishing agent (wet or dry chemical) or a gas that serves as the sole extinguishing agent. I hope this information is helpful. Please contact us if we can be of further assistance. Sincerely, Alexander Wolcott Acting Chief, Regulatory Review & Reinvention Standards and Rulemaking Division#

Page 3Pollack, A. 26-0050 Mr. Shane Kelley Director, Standards and Rulemaking Division U.S. DOT/PHMSA (PHH-10) 1200 New Jersey Avenue, SE East Building, 2nd Floor Washington, DC 20590 Brick Keltner Corporate Shop Trainer Koorsen Fire & Security 2820 N. Webster Indianapolis, In 46219 Telephone 317-225-4 785 Email: brick.keltner@koorsen.com Mr. Kelley, I would like a Formal Interpretation of 49 CFR 180.209U). Cylinder used as a Fire Extinguisher. The questions that I have relate to the testing of Fire Extinguishers as well as the definition of them. In the above standard it states the time frame of the testing intervals. In around July - August 2021 the Transportation of Restaurant/ Kitchen and Dry Chemical Suppression System cylinders was changed to - transport them as UN1044 Fire Extinguishers. I requested a Formal Interpretation (ref# 21-0084) if they were also to be tested as Fire Extinguishers. The answer I received back was, NO - they are not to be tested as Fire Extinguishers, it is just for Transportation. References are from the November 1 , 2025 - 49 CFR MasterRegs 180.209U) states the requirements for testing of Fire Extinguishers and references 173.309(a) for the definition of a Fire Extinguisher. 173.309 - Fire Extinguishers This section applies to portable fire extinguishers for manual handling and operation, fire extinguishers for installation in aircraft, fire extinguishers for installation as part of a fire suppression system, and large fire extinguishers. Fire Extinguishers for installation as part of a fire suppression system include cylinders charged with either a compressed gas and an extinguishing agent in the system or a gas which comprises the sole fire extinguishing agent in the system.#

Page 4180.2090) - states that only DOT cylinders used as a fire extinguisher in conformance with 173. 309( a) of this subchapter may be requalified in conformance with this paragraph 0). 180.2090)(1) A DOT 48, 48A, 48240ET or 48W cylinder used as a fire extinguisher may be tested as follows: (ii) For a cylinder having a water capacity over 5.44kg (12 pounds), by the waterjacket, direct expansion or proof pressure test methods as prescribed in CGA C-1. For proof pressure test, a requalification must be performed by the end of 12 years after the original test date and at seven (7) year intervals. The questions are Does a 48A and/or 48W Restaurant / Kitchen / Paint Booth Suppression cylinder that has a water capacity over 5.44kg (12 pounds) meet the definition of Fire Extinguisher and require to be tested 12 years after the original test date and at 7 years after that? - Does a 48A and/or 48W Restaurant Suppression cylinder that has a water capacity over 5.44kg (12 pounds) and is installed on a mobile Food Truck / Trailer meet the requirement to be tested 12 years after the original test date and at 7 years after that? - Does this apply to both Wet & Dry Chemical Suppression Systems. (i.e. wet chemical - Kitchen/Restaurant as well as dry chemical - Paint Booths) Thank you for any information that you can give me. Brick Keltner, Koorsen Fire & Security#