Interpretation Response #22-0078
Below is the interpretation response detail and a list of regulations sections applicable to this response.
Interpretation Response Details
May 25, 2023
Mr. Jared Sharp
Senior Manager, Transportation Safety
1709 South Burlington Road
Bridgeton, NJ 08302
Reference No. 22-0078
Dear Mr. Sharp:
This letter is in response to your August 2, 2022, email requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to the loading of liquefied petroleum gas (LPG) in Department of Transportation specification MC 331 cargo tanks.
We have paraphrased and answered your questions as follows:
Q1. You ask whether a cargo tank is considered to be "overfilled" if the liquid level gauge is greater than 90% when loading it in accordance with the specific gravity chart provided in § 173.315(b).
A1. When loading a cargo tank motor vehicle (CTMV) with LPG, fillers must follow the requirements of § 173.315(b). This section instructs fillers to load CTMVs by weight based on the capacity of the tanks and the specific gravity of the LPG. When filling the CTMV by volume, the same amount of material is permitted, unless the filler is using a fixed length dip tube or other fixed maximum liquid level indicators, in which case the CTMV may only be filled to 97% of the maximum permitted filling density by weight. Factors such as the temperature may cause fluctuations in the volume reading on a CTMV; however, this is not an upper fill limit of 90%. Provided the filling requirements of § 173.315(b) and the outage requirements of § 173.24b(a) are met, a liquid level gauge may read more than 90% and still be in compliance.
Q2. When using the specific gravity chart provided in § 173.315(b), you ask whether it is permissible to revise your specific gravity values to reflect the current temperature of an LPG product if it is warmer than 60 degrees Fahrenheit.
A2. The answer is no. The table lists the maximum permitted filling density as a percentage of water-weight capacity based on the specific gravity of LPG at 60 degrees Fahrenheit. Since temperature has a direct relation to volume, the regulations are set to this specific temperature and adjustments are not permitted.
Q3. You ask whether the requirement specified in § 173.24b(a)—that the outage is at least 1% of the total capacity of the cargo tank—applies to LPG.
A3. The answer is yes. Section 173.24b(a) states that "[e]xcept as otherwise provided in this subchapter, liquids and liquefied gases must be so loaded that the outage is at least five percent for materials poisonous by inhalation, or at least one percent for all other materials, of the total capacity of a cargo tank, portable tank, tank car (including dome capacity), multi-unit tank car tank, or any compartment thereof...." Section 173.315(b) does not provide relief from the outage requirements of § 173.24b(a).
I hope this information is helpful. Please contact us if we can be of further assistance.
T. Glenn Foster
Chief, Regulatory Review and Reinvention Branch
Standards and Rulemaking Division
|§ 173.315||Compressed gases in cargo tanks and portable tanks|