Routine loss estimation for floating roof and fixed roof organic liquid storage tanks
⬡ AP-42 CHAPTER 7 (9/2025) · API MPMS 19.2
⚠ 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
Tank Type & Geometry
Construction & Rim Seal
Rim-seal loss factors from AP-42 Table 7.1-8.
Stored Liquid
TVP is computed from the liquid surface temperature (below) using the chemical's Antoine constants. 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.
Enter the five values above. Metric entries are converted to US units automatically.
Select a location to compute liquid surface temperature.
Operation
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.
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).
Tank Cleaning — Forced Ventilation
Vapor space purge + continued forced ventilation (AP-42 §7.1.3.4, Eq. 4-2 to 4-10).
Continued Forced Ventilation
Results
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Enter tank parameters and calculate to see standing, working, and total loss estimates.