Maximum Permitted Filling Density

By Mathieu Roy
Last updated: April 12, 2022

What Does Maximum Permitted Filling Density Mean?

The maximum permitted filling density of a product refers to the amount of it that can be safely filled in an appropriate container. It is based on the volume of the product at a temperature of 40°F for above-ground containers, and at 50°F for underground containers.

Safeopedia Explains Maximum Permitted Filling Density

Filling Requirements for Liquefied Natural Gas

The Pipeline and Hazardous Materials Safety Administration (PHMSA) has adopted a 37.3% maximum filling density for liquefied natural gas (LNG). This allows for approximately 2% outage below the inlet of the pressure control valve to prevent the venting of the liquid material at the start to discharge pressure, ensuring safe transportation.

The 37.3% maximum filling density is consistent with outages determined to be safe for LNG in other packagings, such as MC-338 cargo tanks and UN T75 portable tanks. It is also considered more conservative than the maximums set in the Hazardous Materials Regulations (HMR) for other flammable cryogenic materials, which only allow for 0.5% outage at the start to discharge pressure.

It also harmonizes with Canada’s Transportation of Dangerous Goods (TDG) regulations.

Filling Requirements for Liquefied Compressed Gasses

The 49 CFR § 173.304 standard concerns the filling of cylinders with liquefied compressed gasses. It specifies the following:

a.General requirements: A cylinder filled with a liquefied compressed gas except gas in solution, must be transported in accordance with the requirements of this section and that in §173.01of this subpart. A DOT specification cylinder must meet the requirements in §§ 173.301a, 173.304a, and 173.305, as applicable.

b.Filling limits: The liquid portion of a liquefied gas may not completely fill the packaging at any temperature up to and including 55°C (131°F), except for carbon dioxide; 1,1- Difluoroethylene (R-1132A); nitrous oxide; and vinyl fluoride, inhibited.

Additional Filling Requirements

49 CFR § 173.304a provides additional requirements for the shipment of liquefied compressed gases in specification cylinders, which are given a brief mention below.

a.Filling Requirements – Liquefied gases except gas in solution must be transported subject to requirements in this section and in §§ 173.301 and 173.304, in specification cylinders as follows:

1. DOT 3, 3A, 3AA, 3B, 3BN, 3E, 4B, 4BA, 4B240ET, 4BW, 4E, 39, except that no DOT 4E or 39 packagings may be filled and shipped with a mixture containing a pyrophoric liquid, carbon bisulfide (disulfide), ethyl chloride, ethylene oxide, nickel carbonyl, spirits of nitroglycerin, or toxic material unless specifically authorized in this part.

2. Requirements as presented in a table for the gases named, with details regarding kind of gas, the maximum permitted filling density, packaging markings.

The filling density refers to the percent ratio of the weight of gas in packaging to the weight of water that the container will hold at 16°C (60°F).


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