Storage Tanks

Fixed-Roof Tank Losses (AP-42 7.1)

Routine standing and working losses from a vertical fixed-roof tank, following EPA AP-42 Section 7.1.

Activity data shared by every pollutant. Factors and control efficiency are on .

Source name / ID

Vapor space volume (VV)

ft³

Stock vapor density (WV)

lb/ft³

AP-42 Equation 1-24.

Vapor space expansion factor (KE)

per day

Vented vapor saturation factor (KS)

—

AP-42 Equation 1-23.

Annual net throughput (Q)

bbl/yr

Tank diameter (D)

Maximum liquid height (HLX)

Minimum liquid height (HLN)

Working loss product factor (KP)

—

AP-42: 0.75 for crude oils; 1 for all other organic liquids.

Vent setting correction factor (KB)

—

AP-42: KB = 1 for a vent setting range up to ± 0.03 psig.

Flashing loss (site-specific)

lb/yr

0 unless flashing occurs. When it does, KN = 1.

Operating hours

hr/yr

8,760 hr/yr for potential to emit unless an enforceable limit applies.

Method

AP-42 Section 7.1 method for routine losses from a vertical fixed-roof tank. Standing loss comes from the vapor space and daily expansion; working loss from throughput, turnovers, and the product. Flashing losses are not part of LT: estimate them with a site-specific method and enter the result, and if vapors go to a control device, apply its efficiency to all three. WV, KE, and KS come from AP-42's own equations for the liquid and site; enter the values you calculated and keep that work on file.

LT (lb/yr) = LS + LW; LS = 365 × VV × WV × KE × KS; LW = VQ × KN × KP × WV × KB; VQ = 5.614 × Q

Symbols in the formula
Symbol	Meaning	Unit
LT	Total routine losses	lb/yr
LS	Standing loss	lb/yr
LW	Working loss	lb/yr
VV	Vapor space volume	ft³
WV	Stock vapor density (AP-42 Equation 1-24)	lb/ft³
KE	Vapor space expansion factor	per day
KS	Vented vapor saturation factor (AP-42 Equation 1-23)	—
VQ	Net working loss throughput = 5.614 × Q	ft³/yr
Q	Annual net throughput	bbl/yr
N	Turnovers per year = ΣHQI ÷ (HLX − HLN), with ΣHQI = 5.614 × Q ÷ ((π/4) × D²)	—
D, HLX, HLN	Tank diameter, maximum and minimum liquid height	ft
KN	Turnover factor: (180 + N) ÷ 6N when N > 36, otherwise 1; 1 when flashing occurs	—
KP	Working loss product factor: 0.75 for crude oils, 1 for other organic liquids	—
KB	Vent setting correction factor	—
w	Pollutant weight fraction of the vapor (wt % ÷ 100)	—

Official basis: the procedure's own words (27 quotes)

“Total routine losses from fixed roof tanks are equal to the sum of the standing loss and working loss:”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“LT = LS + LW”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“LT = total routine losses, lb/yr”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“LS = 365 VVWVKEKS”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“365 = constant, the number of daily events in a year, (days/year)”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“VV = vapor space volume, ft3”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“WV = stock vapor density, lb/ft3, see Equation 1-24”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“KE = vapor space expansion factor, per day”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“KS = vented vapor saturation factor, dimensionless, see Equation 1-23”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“LW = working loss, lb/yr”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“5.614 Q (when ΣHQI is unknown; equation 1-41)”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“5.614 = the conversion of barrels to cubic feet, ft3/bbl”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“Q = annual net throughput, bbl/yr”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“N = number of turnovers per year, dimensionless:”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“ΣHQI =(5.614) (201.2) / ((π/4) 62) = 39.9 ft”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“N =39.9 / (11.5 – 4.5) = 5.7”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“for turnovers > 36, KN = (180 + N)/6N”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“for turnovers £ 36, KN = 1”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“for tanks that are vapor balanced and tanks in which flashing occurs, KN = 1 regardless of the number of turnovers”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“for crude oils, KP = 0.75;”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“for all other organic liquids, KP = 1”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“for a vent setting range up to ± 0.03 psig, KB = 1”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“LS = (365)(0.0143)(169.6)(0.108)(0.888)”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“LW = (5.614)*(201.2)* (1)*(1)*(0.0143) (1) = 16.1 lb/yr”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“There are numerous methodologies available for estimating flashing losses and specific guidance regarding their application and use.”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“This scenario is typical of storage tanks receiving liquids from a separator in oil and gas production operations”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)
“If vapors are routed to a control device, the control efficiency of the device should be applied to the flashing loss as well as to the standing and working losses.”
EPA AP-42, Section 7.1, Organic Liquid Storage Tanks (6/2026)

This method needs no emission factor. WV, KE, and KS come from AP-42 Section 7.1's equations for your liquid and site; the vapor weight fraction comes from a vapor analysis or speciation. Cite each.

Pollutants and factors

Pollutant 1: VOC
Pollutant
Pollutant weight fraction of the vapor
%
Control efficiency
%
Only claim control you can document and enforce.
Input source / reference
Section / table
Source URL
Revision date

Emissions results

Enter vapor space volume (vv), stock vapor density (wv), vapor space expansion factor (ke), … on the Inputs tab.

VOC
Needs pollutant weight fraction of the vapor

Uncontrolled and controlled emissions by pollutant
Pollutant	Uncontrolled (lb/hr)	Controlled (lb/hr)	Controlled (lb/day)	Controlled (tons/yr)
VOC	Needs pollutant weight fraction of the vapor (Method & Factors tab)

Annual values assume 8,760 hr/yr and each pollutant's control efficiency.

Emissions results

Enter vapor space volume (vv), stock vapor density (wv), vapor space expansion factor (ke), … on the Inputs tab.

VOC
Needs pollutant weight fraction of the vapor

Uncontrolled and controlled emissions by pollutant
Pollutant	Uncontrolled (lb/hr)	Controlled (lb/hr)	Controlled (lb/day)	Controlled (tons/yr)
VOC	Needs pollutant weight fraction of the vapor (Method & Factors tab)

Annual values assume 8,760 hr/yr and each pollutant's control efficiency.

Calculation set

Saved calculations from every calculator, totaled by pollutant. Kept in this browser until accounts launch.

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Fixed-Roof Tank Losses (AP-42 7.1)

Inputs

Method & Factors

Method

Pollutants and factors

Results

Emissions results

References

Factor references

Related regulations

Emissions results

Calculation set