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surrounding temperature and barometric pressure, and working emissions, which result from the
loading or withdrawal of fuel. In both cases, emissions result from higher pressure inside the tank
than outside, causing the hydrocarbon vapor to escape through any available opening. Depending
on the tank type, these openings or pathways include breather vents, rim seals, deck fittings, and
deck seams.
4 Sources: EPA’s "Fuel Storage Tanks," Compilation of Air Pollutant Emission Factors, Volume I, Section
7.1. and Jagielski, Kurt D., and Robert J. O'Brien, Calculation Methods for Criteria Air Pollutant
Emission Inventories, p. 14.
H-20
The general methodology for calculating storage tank hydrocarbon emissions may be expressed
by Equation H-8:
EHC = ES + EW
Where:
EHC - total hydrocarbon emissions from a single tank over a given time
period
ES - standing storage emissions from the tank
EW - working emissions from the tank
Equation H-8: Hydrocarbon Emissions for Storage Tanks
The methodologies for calculating ES and EW are different for each tank type. These
methodologies are described in the Section 7.1, Volume I of Compilation of Air Pollutant
Emission Factors, and are implemented in the EPA computer model TANKS (Reference 84).
H3.1.2 Data Sources
A number of data sources are required for an accurate assessment of standing storage and
working emissions from fuel storage tanks. These include the type of tank, physical dimensions
of the tank, fuel type, climatic data, rate of fuel throughput, and other tank-specific
characteristics. Detailed information on data requirements is given in Section 7.1, Volume I of
Compilation of Air Pollutant Emission Factors. An overview of these requirements and the likely
sources of obtaining this information is given in paragraphs 3.1.2.1. through 3.1.2.5.
H3.1.2.1 Type of Storage Tank
The three most common main types of fuel storage tanks are fixed roof, external floating roof,
and internal floating roof tanks. Descriptions of the different tank types is given in Section 7.1,
Volume I of Compilation of Air Pollutant Emission Factors. Tank information may be obtained
from the airport operator, base operations department, fueling contractor, or by visual inspection.
H3.1.2.2 Fuel Type
Fuel vapor pressure and density for each storage tank are required to calculate emission losses.
Specification of the type of fuel stored in the tank allows the use of default values for vapor
pressure and density given in Section 7.1, Volume I of Compilation of Air Pollutant Emission
Factors and included in the TANKS program.
H3.1.2.3 Climatic Data
Average wind speed, average daily ambient temperature range, average daily solar insulation,
and average atmospheric pressure values are each required for the emission calculation. The EPA
program TANKS contains a database of the necessary climatic information for over 250 cities in
the United States, so that only the closest nearby city needs to be specified by the user.
H-21
H3.1.2.4 Fuel Throughput
An estimate of annual throughput of fuel for each tank should be obtained from the airport
operator, fueling contractor, or base operations department.
H3.1.2.5 Tank-Specific Characteristics
Tank-specific characteristics used in calculating emission losses include one or more of the
following: physical dimensions of the tank, type of seals, breather vent settings, tank paint color,
number of vacuum breakers, number of columns, effective column diameter, deck fitting types,
and deck seam length. This information may be obtained from the airport operator, fueling
contractor, base operations department, tank manufacturer, or by visual inspection of the tank. In
many cases, default values are given in Compilation of Air Pollutant Emission Factors and are
incorporated into the TANKS program.
H3.2 Coating or Painting Operations
H3.2.1 Methodology
Painting operations emit volatile hydrocarbons (HC) to the atmosphere through evaporation of
the paint vehicle, thinner, or solvent used to facilitate the application of the coatings. The main
factor affecting HC emissions from painting operations is the volatile content of the coatings,
which averages around 15% for water-based coatings to over 50% for solvent-based coatings5.
Most, if not all, of the volatile portion of the coating evaporates during or following application.
To reduce these emissions, paint manufacturers have reduced the VOC content of coatings in
recent years. In addition, air pollution control equipment, such as activated carbon adsorption of
hydrocarbon emissions or destruction of hydrocarbons in an afterburner, is available for use in
some applications.
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