The official tank emissions calculation methodology designated by U.S. EPA is specified in AP-42 Chapter 7.1. TANKS 4.09d (TANKS) is a software program developed and copyrighted by the American Petroleum Institute (API), and was designed to conduct calculations based on the methodology outlined in AP-42 Chapter 7.1. This software has been widely used to estimate VOC emissions from storage tanks across numerous industries. However, in 2014, U.S. EPA released a statement that they are no longer supporting the use of TANKS, as there are compatibility issues with certain computer operating systems. Although the model will remain on the EPA website, U.S. EPA and other state agencies (i.e., Texas Commission on Environmental Quality [TCEQ]) recognize the existence of some software defects within TANKS that prohibit it from correctly calculating emissions and are now recommending the use of the equations found in AP-42 Chapter 7 equations to calculate emissions.
Specifically, regulatory agencies and industry experts have determined that TANKS does not correctly calculate emissions for the following scenarios:
- Heated tanks;
- Uninsulated tanks receiving and storing warm products;
- Tanks with significant variations in throughput on a monthly basis; and
- Tanks located in areas with high ambient temperature.
For the above scenarios, tank emissions should instead be calculated using the equations found in AP-42 Chapter 7 in conjunction with an alternative spreadsheet or software program.
Please contact Garrett Koehler at (614) 433-0733 if you have any questions regarding this article and alternative tank emissions calculation tools.