Table A5-3. Evaporative Emission Losses of Fuel Storage Tanks  Tank Type 1  Evaporative Emission Losses  Horizontal  Potential evaporative emission sources for above -ground horizontal tanks  are the same as those for  fixed-roof tanks. Emissions from underground  storage tanks are mainly associated with changes in the liquid level in the  tank. Losses due to changes in temperature or barometric pressure minimal for underground tanks because the surrounding earth limit s the diurnal temperature change and changes in the barometric pressure would  result in only small losses.  Vertical Fixed Roof 2  Breathing losses  are expelled via vents during temperature and pressure - induced expansions and contractions.  Working losses  are evaporative losses produced during filling emptying operations. As the tank is filled, the vapor pressure within exceeds the relief pressure and vapors are expelled from the tank. During  fuel removal, air drawn into the tank to replace the liqu id becomes saturated with organic vapor and expands, thereby exceeding the capacity  of the vapor space and exiting through the pressure-vacuum relief valve.  Internal Floating Roof 3  Rim seal, deck fitting, and deck seam losses  occur in internal floating roof  tanks due to slight imbalances in internal and external pressure.  Withdrawal losses  are similar to those for external floating roof tanks with  one major difference--wind is not a predominant factor affecting rim seal  losses.  External Floating Roof 3  Standing storage losses  emanate from roof fittings and rim seals --which  occupy the space between the edge of the floating roof and the tank wall.  Some breathing losses also occur. Most of these losses are wind-induced.  Withdrawal losses  occur during removal operations, fuel remains attached  to the tank wall and evaporates as the fuel level, and thus the floating roof,  is lowered.  Domed External Floating  Roof 4  This type of tank is very similar to an internal floating roof tank with welded deck and a self-supporting fixed roof. As with the internal floating  roof tanks, the function of the fixed roof is not to act as a vapor barrier, but  to block the wind. Like the internal floating roof tanks, freely vented by circulation vents at the top  of the fixed roof. The d eck fittings and rim seals, however, are basically identical to those on external  floating roof tanks.  Source:  Emissions and Dispersion Modeling System (EDMS) User’s Manual , FAA-AEE-07-01 (Rev. 10 –  06/07/13), June 2013,  http://www.faa.gov/about/office_org/headquarters_offices/apl/research/models/edms_model/media/EDMS_5.1.4_  User_Manual.pdf, and Chapter 7,  Organic Liquid Storage Tanks,  of EPA's AP-42,  http://www.epa.gov/ttnchie1/ap42/ch07/.  Notes:  1  Tanks listed are typically above ground storage tanks, except for horizontal fixed roof  tanks which can be constructed for both above-ground and underground service. $^{2 }$In general, fixed-roof tanks tend to be older and result in the greatest atmospheric emissions. The presence of a  volume of vapor space above the level of liquid in the tank promotes evaporation of the fuel hydrocarbons and their  subsequent release to the atmosphere through the breather valve. 3  Tanks equipped with a floating roof are able to reduce evaporative emissions by eliminating the vapor sp between the liquid level in the tank and the tank roof. However, some emissions do occur through various seals and  32$_{ }$ APPENDIX A5$_{ }$