APPENDIX B$_{ }$ B.2.4.2 Emission Factors  The MOVES emission rates, when c oupled with estimates of travel activity (vehicle -miles- traveled or VMT), provide estimates of the mass of  HAP as shown in  Equation B-7  ( HAP  Emissions - Ground Access Vehicles ).  I = D x N x 1/1000  Where:  I = Mass of HAP of interest (kg)  D = HAP emission index, expressed in grams per mile (g/mi)  N = Vehicle-miles-traveled, expressed as miles (mi)  1/1000 = Conversion factor from grams to kilograms  B.2.5  Stationary Combustion Sources  Potential stationary combustion sources of HAPs at airports include  boilers/space heaters,  generators, incinerators, fire training facilities, and aircraft engine testing . The data required to  prepare a HAP emission inventory for these sources include: (i) the amount of fuel consumed  over a given time period, (ii) a THC emission index, (iii) a THC-to-TOG conversion factor, and  (iv) a HAPs speciation profile. In nearly all cases, the types and amounts of HAP emitted by  these sources depend on the type and quantity of the fuel used, operating times, and the existence  of emission control equipment.  HAP emissions from fuel storage tanks vary by fuel type and vapor pressure; containment vessel,  emission control device, fuel throughput volumes, and local meteorological conditions.  59$_{ }$ B.2.6  Fuel Storage Tanks  Where:  I = Mass of HAP of interest, expressed in pounds (lbs)  Equation B-8  ( HAP Emissions - Stationary Combustion Sources ) provides a methodology to  estimate of HAP emis sions for an individual stationary combustion source. EDMS /AEDT  provides THC to TOG conversion factors for various equipment and fuel.  I = C x D x F x H  C = Total fuel consumed, expresses in gallons (for liquid fuels), million cubic feet (for  natural gas), or tons (for coal)  D = THC emission index, expressed in pounds per gallon (lbs/gal) for liquid fuels, pounds  per million cubic feet (lbs/10$^{6 }$cf) for natural gas, or pounds per ton (lbs /ton) for coal  F = THC to TOG conversion factor (unitless)  Equation B-7. HAP Emissions - Ground Access Vehicles  Equation B-8. HAP Emissions - Stationary Combustion Sources 