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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Interpretation Response #03-0167 ([McCarthy, Sweeney & Harkaway, P.C.] [Mr. Lawrence W. Bierlein])

Below is the interpretation response detail and a list of regulations sections applicable to this response.

Interpretation Response Details

Response Publish Date:

Company Name: McCarthy, Sweeney & Harkaway, P.C.

Individual Name: Mr. Lawrence W. Bierlein

Location State: DC Country: US

View the Interpretation Document

Response text:

Sep 29, 2003


Mr. Lawrence W. Bierlein               Reference No. 03-0167
McCarthy, Sweeney & Harkaway, P.C.
Suite 600
2175 K Street, N.W.
Washington, D.C. 20037

Dear Mr. Bierlein:

This responds to your June 23, 2003, letter requesting clarification on the applicability of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) to capillary tube thermostats produced by Therm-O-Disc, a division, of Emerson Electric.   Specifically, you ask for concurrence that these thermostats containing a small amount of flammable liquid charging material, sealed within each control, and packaged as described, are not regulated under the HMR.

According to your letter, these thermostats are used in baseboard heater applications.  Expansion and contraction of the charging fluid in a fine tube, under varying temperatures, exerts pressure on a bellows diaphragm located in the metal cup.  This activates the switching of the control.

These thermostat controls are manufactured in various temperature control ranges and tube lengths.  The lower temperature-rated controls utilize methanol and water as a charging mixture that is drawn into the small copper tubing during manufacture.  Fluid volumes are very small, with the least material holding approximately 1 milliliter of charging liquid, and up to 4.4 milliliters in the largest version.  The entire unit is hermetically sealed under vacuum.

The units are packed in a fiberboard carton with 200-400 units per carton, each separated from the others in an egg-crate style inner packaging configuration, with a solid fiberboard divider separating the layers within the carton. Each control is physically separated from the other controls on all six sides.  The units are sealed and do not leak.  If one were broken, capillary action would tend to hold the small amount of charging fluid inside the control.

Under § 173.22, it is the shipper's responsibility to properly class and describe a hazardous material.  This Office does not generally perform that function.  According to your letter, your capillary tube thermostats contain methanol (Class 3, Flammable liquid) and water used as a charging mixture.  Section 173.150(e) pen-nits aqueous solutions of alcohol containing 24 percent or less alcohol by volume and no other hazardous material to be reclassed as a combustible liquid.  Further, under § 173.150(e), an aqueous solution containing 24 percent or less alcohol by volume and no other hazardous material is excepted from the HMR if it contains no less than 50 percent water.  You did not provide more specific information on the methanol and water mixture to enable this Office to provide you with a more specific opinion on the hazard class of these thermostats.  However, based on the information you provided, if the capillary tube thermostats containing small amounts of the methanol and water charging mixture

do not meet the hazard class defining criteria in Part 173, and are not a hazardous waste, hazardous substance, or marine pollutant, they are not subject to the HMR.

I hope this answers your inquiry.



Susan Gorsky
Senior Transportation Specialist
Office of Hazardous Materials Standards


Regulation Sections

Section Subject
171.1 Applicability of Hazardous Materials Regulations (HMR) to persons and functions