The EPA has proposed revisions to Chapter 7, Section 7.1 (revisions to AP-42 Chapter 7, Section 7.1). In response to a request for comments, Mitchell Scientific has submitted a proposal to use the actual vapor space volume using conventional geometry rather than one that is based solely on the tank dimensions when calculating the breathing emissions from a horizontal storage tank.

A key variable to be calculated when estimating the breathing losses for a fixed roof storage tank is the vapor space volume. If the storage tank is a vertical cone or dome top style then the vapor space volume is calculated from the size of the vessel and the liquid volume. However, if the storage tank is horizontal in design then the vapor space volume is estimated from only vessel dimension parameters.

Read the full proposal here: Horizontal_Storage_Tank_2018-11-06.pdf

The document for download provides the following discussion:

(1) The existing procedures for calculating Vv and Hvo are reviewed.

(2) A newer more equation for calculating Vv that is based an accurate determination of the liquid contents volume VL is proposed.

(3) The newer approach for calculating Vv is applied to Example #2 as contained in Chapter 7.1 and the results are compared to the current methodology.

(4) A mathematical derivation of the proposed new equation for calculating the volume of liquid in the horizontal storage tank is provided.