⚠ Indicative estimates only — per US EPA AP-42 Ch. 7 / API MPMS 19.2. Not valid for regulatory compliance, permitting, or reporting. Full terms accepted at sign-in; the complete disclaimer is included in every downloaded report.
Tank Identification
Research entries stay private to you for practice/testing. Switch to Official once this is a real assessment your company should see.
Components (Speciation, AP-42 §7.1.4) optional
Estimate losses of individual components such as benzene. Enter each component's weight percent in the liquid; the tool applies Raoult's law at the liquid surface temperature (Eqs 40-3 to 40-6) and splits every loss into components (Eqs 40-1 and 40-2).
ML defaults from AP-42 Table 7.1-2 for gasoline (92) and crude oil (207); AP-42 gives none for naphthas, so enter your stock's value. Raoult's law assumes ideal mixing, which AP-42 finds reasonable for most hydrocarbon mixtures but not for aqueous mixtures or mixtures containing alcohols. Floating-roof withdrawal loss uses the liquid composition, because the film on the shell evaporates completely (Eq 40-2); substances that are non-subliming solids at storage temperature, such as most polycyclic aromatic hydrocarbons, won't evaporate from that film. Mixed xylenes are usually represented by m-xylene, as in AP-42's examples.
Stored Liquid
AP-42 calculates the vapor pressure of naphthas and gasolines from RVP (ASTM D323 or D5191) and the distillation slope S at 10% evaporated. If you have a D86 report, enter the 5% and 15% evaporated temperatures and S is derived as (T15 − T5)/10 in °F; these take priority over a typed S. Without lab data, AP-42 Table 7.1-2 defaults apply: gasoline 3.0, light naphtha (RVP 9–14) 3.5, naphtha (RVP 2–8) 2.5. Crude oil uses RVP only. The method covers RVP 1–20 psi for refined stocks. Below 1 psi RVP the method doesn't apply — measure true vapor pressure (ASTM D2879) and use “Enter TVP directly”.
TVP is computed from the liquid surface temperature (below) using Antoine constants for chemicals or the AP-42 RVP equations for petroleum stocks. Product factor KC = 0.4 for crude oils, 1.0 otherwise (AP-42 Eq. 2-4).
Location & Environment
Liquid surface temperature is derived from site meteorology, solar insolation, and paint color — AP-42 Eq. 2-5 to 2-12, Tables 7.1-6 & 7.1-7.
🌐 CUSTOM SITE METEOROLOGY
Enter values in:
Use 30-year climate normals for the tank site (to match AP-42's basis), not a single year or current weather.
Values are stored internally in US units — the calculation always runs per AP-42 / API MPMS 19.2.
AUTO-FILL FROM NASA POWER — ANY LOCATION WORLDWIDE
If your browser blocked the request: open this NASA POWER data link in a new tab, wait for it to load (it can take a minute), select all, copy, and paste it below.
Fills the five values below from NASA POWER daily data (MERRA-2 reanalysis and satellite solar), averaged over 30 full years to match AP-42's climate-normal basis: daily maximum and minimum temperature, wind speed at 10 m (AP-42's measurement height), solar insolation, and surface pressure. Wind is modelled on a grid of roughly 55 × 65 km, so a coastal terminal can differ from its own anemometer — if you have IMD station normals or site measurements at 10 m or above, overwrite the filled value. Coordinates in the list are approximate; enter your tank's own coordinates for best results.
Enter the five values above. Metric entries are converted to US units automatically.
Select a location to compute liquid surface temperature.
Operation
Enter net throughput. If the tank is filled and emptied at the same time, gross throughput overstates working loss (AP-42 Eq 1-41 note). If you know the annual sum of liquid-level changes, enter it instead: the tool uses level increases for fixed roofs (Eq 1-40) and level decreases for floating roofs (Eq 2-20). Over a year the two are approximately equal.
Monthly mode runs the routine floating- or fixed-roof calculation once per month with that month's weather (AP-42 Table 7.1-7 for listed US locations; the NASA POWER auto-fill for custom sites) and adds the 12 months. AP-42 recommends one month as the shortest period. Landing and cleaning are single events, so they always use the annual climate.
Wind speed auto-fills from the selected location (Table 7.1-7) and can be overridden. Used only for external floating roof tanks; internal & domed external tanks use v = 0. AP-42's rim-seal and deck-fitting factors are valid only for average wind below 15 mph.
Tank Type & Geometry
Construction & Rim Seal
Rim-seal loss factors from AP-42 Table 7.1-8.
Shell Condition & Columns
Withdrawal (working) loss inputs — AP-42 Eq. 2-19, Table 7.1-10.
Deck Seam (Internal FR only)
Deck seam loss applies to bolted decks only — AP-42 Eq. 2-18, Table 7.1-16.
Deck Fittings
Add each fitting and its count. Loss factors from AP-42 Table 7.1-12. Fittings marked IFR-only cannot be used on external tanks (no wind term).
Tank Geometry
Horizontal tanks use an effective diameter DE = √(LD·4/π) and effective height HE = (π/4)D (AP-42 Eq. 1-14/1-15).
Breather Vent & Pressure
Default settings ±0.03 psig if unknown (AP-42 Note 3 to Eq. 1-5).
Roof Landing Event
Emissions from a floating roof landing — standing idle loss + filling loss (AP-42 §7.1.3.3, Eq. 3-7 to 3-18). AP-42 takes the temperature under a landed roof as the average ambient temperature for the month in which the landing occurs, so choose that month below.
Height of the floating roof above the tank floor when it rests on its legs. The vapor space during a landing is only the space under the roof (AP-42 §7.1.3.3: hv = leg height − heel height), not the full shell.
The stock in Stored Liquid is the heel left under the landed roof; it sets the standing idle loss and the arrival vapors. AP-42 §7.1.3.3: on a change of service the filling loss is split into an arrival component (prior stock, saturation CsfS − 0.15) and a generated component (incoming stock, saturation 0.15). For a drain-dry tank only the generated component applies.
Tank Cleaning — Forced Ventilation
Vapor space purge + continued forced ventilation (AP-42 §7.1.3.4, Eq. 4-2 to 4-10). The vapor space is taken at the average ambient temperature; choose the month the cleaning takes place to use that month's weather.
Continued Forced Ventilation
Results
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Enter tank parameters and calculate to see standing, working, and total loss estimates.