Interpretation Response #26-0050
Below is the interpretation response detail and a list of regulations sections applicable to this response.
Interpretation Response Details
Response Publish Date:
Company Name: Koorsen Fire & Security
Individual Name: Brick Keltner
Location State: IN Country: US
View the Interpretation Document
Response text:
July 28, 2026
Mr. Brick Keltner
Corporate Shop Trainer
Koorsen Fire & Security
2820 N. Webster
Indianapolis, IN 46219
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 thereafter. 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 and Reinvention Branch
Standards and Rulemaking Division
173.309(a)(1)-(5) 180.209(j)(1)(ii)