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This letter is in response to your November 23, 2016, letter and subsequent phone conversations requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to the classification of a hazardous material. Specifically, you indicate that your company markets a Rubidium oscillator/Atomic clock containing less than one (1) gram of rubidium and ask if it meets the definition of a Class 4 hazardous material. You note that a previous PHMSA interpretation (Reference No. 08-0154) indicates that when less than one gram of rubidium is contained in an atomic clock it does not pose a risk during transportation and is not subject to the HMR. Furthermore, you provided test data of both an impact and drop simulation. The results of the test demonstrate no evidence of spontaneous combustion or damage to the capsule or the oscillator.
In accordance with § 173.22, it is the shipper's responsibility to class and describe a hazardous material in accordance with Parts 172 and 173 of the HMR. Note that previous interpretations were not a determination of whether rubidium is a Class 4 hazardous material but whether the amount and form in which it is transported presents an unreasonable risk to health and safety or property. This Office does not generally perform this function. However, based on the subsequent test data you have provided and previous PHMSA interpretation, it is the opinion of this Office that as long as the one gram or less of Rubidium in your atomic clock is hermetically sealed in glass, and the glass capsule is adequately protected from breakage and is an integral internal component of the atomic clock, and the atomic clock does not meet the definition of any other hazard class, it is not subject to the HMR.
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