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Understanding High Purity LPG Fill Ratios: What’s Legal, What’s Safe, and Why It Matters


Solvent Direct prioritizes efficiency for extractors by maximizing fill weights per DOT and PHMSA regulations.
Solvent Direct maximizes fill weights within PHMSA and DOT limits to deliver the highest value on ultra-high purity butane, propane and isobutane gases used in extract manufacturing applicaitons.

Understanding LPG Fill Ratios: What’s Legal, What’s Safe, and Why It Matters

When it comes to liquefied petroleum gas (LPG) used in extraction—like high purity butane, isobutane, and propane—there’s more to filling a cylinder than just “topping it off.” Behind every legally compliant fill is a standard governed by the Pipeline and Hazardous Material Safety Administration (PHMSA) under the Department of Transportation (DOT).


Let’s break it down for the inquiring minds looking for truth, justice, and extraction efficiency.


When it comes to liquefied petroleum gas (LPG) used in extraction—like high purity butane, isobutane, and propane—there’s more to filling a cylinder than just “topping it off.” Behind every legally compliant fill is a standard governed by the Pipeline and Hazardous Material Safety Administration (PHMSA) under the Department of Transportation (DOT).

🔍 What Are Fill Ratios?

Fill ratios determine the maximum amount of liquefied gas that can legally be put into a DOT/UN cylinder. The ratios are based on the water capacity (WC) of the cylinder—essentially, how much water it holds—and are defined per gas type. These

standards are outlined in the U.S. DOT's


UN Recommendations on the Transport of Dangerous Goods.

Here’s the standard fill ratio per gas:

  • Butane: 0.51 (Page 12)

  • Isobutane: 0.49 (Page 13)

  • Propane: 0.42 (Page 12)


🧮 Putting Math into Practice

Let’s use a common example: a LP 239 cylinder, typically referred to as a “100-pounder.” Here’s what the math says:


  • Propane: 239 * 0.42 = 100.38 lbs ➡️ Filled to 100 lbs

  • Butane: 239 * 0.51 = 121.89 lbs ➡️ Filled to 120 lbs

  • Isobutane: 239 * 0.49 = 117.11 lbs ➡️ Filled to 116 lbs


Why the slight reduction? Industry standards. These numbers are slightly below the max to accommodate temperature fluctuations and ensure safety.


When it comes to liquefied petroleum gas (LPG) used in extraction—like high purity butane, isobutane, and propane—there’s more to filling a cylinder than just “topping it off.” Behind every legally compliant fill is a standard governed by the Pipeline and Hazardous Material Safety Administration (PHMSA) under the Department of Transportation (DOT).

⚗️ The 70/30 Blend Breakdown

For common extraction blends like 70% butane / 30% propane, here's how it works:

  • Propane: (239 0.42) 30% = 30.11 lbs

  • Butane: (239 0.51) 70% = 85.32 lbs

  • Total Max Fill = 115.43 lbs ➡️ Industry standard = 115 lbs


Some states (looking at you, Texas 👀) might try to simplify the blend math, but even their “simple” calculations—30 lbs propane + 84 lbs butane = 114 lbs—come within 1% of industry standards. In short: there’s no meaningful difference, but precision still matters.


✅ Why It Matters

Using the correct fill ratio:

  • Keeps you compliant with federal safety regulations

  • Protects against overfilling-related hazards

  • Prevents unnecessary scrutiny from regulators and law enforcement

  • Keeps your team and customers safe


So next time you see a cylinder marked "LP 239," you’ll know that science, math, and compliance all played a part in determining how much LPG it’s holding.


Learn more about the harsh economics of under-filled cylinders: https://www.solventdirect.com/post/fillweights



For more compliance education, visit www.solventdirect.com/compliance

Engineered for Extraction™


 
 
 

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