Is It Time to Reevaluate Your Storage Tank Calculations?

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Storage tank emissions calculations by nature are fairly easy to generate and similarly fairly easy to take for granted. The calculations often remain untouched as methodologies rarely change absent significant updates to Chapter 7, Section 1 (Organic Liquid Storage Tanks) of the USEPA’s AP-42 guidance. While the USEPA made some changes in the latest version of Chapter 7 issued in October of 2024, the last major revision occurred in 2019 and it is likely many sites haven’t given much thought to their tank calculations since that time. However, last year, the USEPA released TANKS 5.1 replacing TANKS4.09 which has been unsupported since 2012. In fact, many agencies ceased allowing the use of TANKS4.09, driving many facilities to explore using third party calculations or to create their own internal tools. With the release of the free-for-use TANKS 5.1 and since we are past the majority of states’ emissions inventory submittal deadlines, now may be a good opportunity to reevaluate your storage tank calculations.

TANKS 5.1 is a browser-based application built with JavaScript available through the USEPA’s website (https://www.epa.gov/air-emissions-factors-and-quantification/tanks-emissions-estimation-software-version-5) that mirrors the current version of Chapter 7.1 of AP-42. The tool will calculate both routine and non-routine for fixed and floating roof tanks, as well as rectangular tanks. It also has the ability to calculate heating cycles, tight-fitting seal losses, and adjusted emissions based on the efficiency of an add-on control device. The application is fairly customizable, allowing the input of custom organic liquids, petroleum liquids, mixtures, and meteorological data.

However, there are a few items to be aware of before committing to a wholesale switch to TANKS 5.1. A few key points to note are as follows:

  • Depending on the number of tanks and customized data used by a given site, the initial data population could require a significant time investment as there is no easy method to mass upload information.
  • While the application is free and easy to use, it is not transparent enough to see the results of the many detailed calculations contained in Chapter 7.1, and there is no emissions report readily exportable in a format for use in permit applications or emissions reporting.
  • TANKS 5.1 stores data in the computer’s local browser storage. This means if the user’s browser cache is cleared and data has not been exported, all tank information will be lost.
  • There is no option to calculate short-term emissions (ie., time periods less than 1 month), nor can a stock change occur during a given month.

The next update to TANKS 5.1 that may resolve some of these issues is expected in 2026.

In spite of some of these concerns, it is a positive to have an accurate, free of charge option for tank calculations mitigating the need to create tools internally or pay licensing fees to use a third-party product. We at TRICORD will continue to monitor TANKS 5.1 as it evolves and will evaluate future updates for accuracy and easy of use. Please reach out to us if you have any questions about TANKS 5.1 or storage tank emissions calculations in general.