United States 

Environmental 

Protection Agency

Office of Enforcement 

and Compliance 

Assurance (2201A)

EPA 325-F-012-002

Enforcement Alert

EPA Enforcement Targets Flaring 

Efficiency Violations

Purpose

EPA is devoting significant enforcement resources to 

correcting regulatory noncompliance at flares. This Alert 

is intended to inform flare owners and operators of this 

enforcement initiative and to educate them on proper flare 

operation. EPA hopes this Alert will spur improvement of flare 

operating practices, including better control and monitoring 

of supplemental gas, air, and steam, and thereby reduce 

harmful emissions to the environment. Better flare operation 

practices will have the potential to improve public health by: 

1) reducing emissions of toxic air pollutants that may pose 

a health risk; and 2) reducing volatile organic compound 

emissions which will in turn reduce the formation of ozone 

which is potentially harmful to vulnerable populations 

including the young, elderly, and those with respiratory 

problems. Moreover, improving flare combustion efficiency 

can result in cost savings due to reduced steam usage.

Introduction

Chemical and petroleum facilities generate waste gases 

that need to be controlled safely, economically, and in a 

manner that protects the public health and the environment. 

The law requires facilities to use good air pollution control 

practices to minimize the emission of waste gases, see 

EPA’s October 2009 Enforcement Alert, http://www.epa.

gov/compliance/resources/newsletters/civil/enfalert/flaring.

pdf. 

Because, not all waste 

gases can be prevented or 

recovered, various control 

technologies are used 

to reduce the impact of 

these waste streams on the 

environment; one common 

technology is flaring. A flare 

is a mechanical device used to combust and thereby destroy 

volatile organic compounds, toxic compounds, and other 

pollutants at refineries and other industrial sites. 

Through its inspection and enforcement programs, 

EPA has identified many instances where flares have been 

improperly monitored and operated. The consequences 

are lower combustion efficiency and potentially significant 

quantities of excess emissions of volatile organic chemicals, 

sometimes including hazardous air pollutants. 

Flare Design Characteristics

Flares are specifically designed to combust gases. Many 

flares employ steam or air to promote mixing of oxygen 

within the Vent Gas to ensure 

combustion occurs without smoke. 

There are many parameters that 

affect the combustion efficiency of 

a flare. One important parameter is 

the heating value of the gases that 

are to be combusted, often measured 

in BTU/scf. The heating value is a 

measure of the combustibility of the 

gas. Generally, it is easier to maintain a stable flame and 

achieve high efficiency for gas streams with higher heating 

Volume 10, Number 5 Office of Civil Enforcement August 2012

http://www.epa.gov/compliance/resources/newsletters/civil/enfalert/index.html

Federal requirements for flares are found in the 

New Source Performance Standards (NSPS) in 

§ 60.18 and National Emission Standards for 

Hazardous Air Pollutants (NESHAP) in § 63.11. 

At a minimum, these rules require flares to be:

• Designed and operated with no visible emissions 

using EPA Method 22 (except for periods not to 

exceed 5 minutes in 2 hours);

• Operated with a flame present at all times, confirmed 

by the use of a thermocouple or equivalent device;

• Used only when the net heating value of the gas to be 

combusted is 300 BTU per standard cubic foot (BTU/

scf) or greater (if the flare is steam- or air-assisted), 

or 200 BTU/scf or greater (if the flare is nonassisted); 

and

• Designed for and operated with an exit velocity less 

than 60 feet per second (ft/sec). An exit velocity of 

greater than 60 ft/sec but less than 400 ft/sec may 

be used if the net heating value of the gas being 

combusted is sufficiently high.

EPA investigations have found 

flares that were operated so 

poorly that there was likely no 

combustion taking place at all. 

In these circumstances the flare 

was merely venting pollution 

directly to the atmosphere. 

S m o k e i s a n 

i n d i c a t i o n t h a t 

hydrocarbons are 

not being combusted 

completely.
Enforcement Alert

August 2012 2

values. The NSPS and NESHAP requirements regulate the 

net heating value and require gases contain at least 300 BTU/

scf if they are being combusted in an air or steam assisted 

flare. If this heating value minimum cannot be met by the 

Vent Gases alone, then supplemental gas, such as natural 

gas, must be added.

Federal regulations prohibit extended periods of smoking 

at flares. Adding the proper amount of steam or air to 

avoid smoke is beneficial, but adding excessive amounts is 

detrimental. Excess steam or air mixed with the Vent Gas 

cools the flame and dilutes the Vent Gas thereby lowering 

the heating value. Steam addition is usually measured as the 

ratio of pounds of steam per pounds of Vent Gas (lb/lb). There 

is no single steam-to-Vent Gas 

ratio that is appropriate for all 

flares. The types of compounds 

being combusted, and to some 

extent the flare design, determine 

the proper ratio. There are, 

however, general guidelines 

that suggest approriate ratios, 

with the most important 

being the manufacturers’ 

recommendations, which tend 

to be between 0.1 and 1lb steam per lb of Vent Gas.

In addition to the numeric standards governing flares 

(e.g., net heating value, exit velocity), there are NSPS and 

NESHAP general provisions that require process and pollution 

control equipment be operated using good air pollution 

control practices to minimize emissions, and in accordance 

with the equipment’s design. Since it would be impossible 

for EPA to list all “common practice” actions for equipment 

owners (e.g., keep equipment from freezing, keep electrical 

equipment dry), these two narrative standards minimally 

require a flare operator to follow the equipment manufacturers’ 

specifications, and to stay abreast of and apply the current state 

of scientific knowledge on flare operation and combustion to 

minimize emissions. 

A number of studies have been conducted to assess 

flare efficiencies and to identify the factors that affect flare 

performance. One simple and critical parameter already 

mentioned is the steam-to-Vent Gas ratio. Another parameter 

with an even better correlation to combustion efficiency for 

steam assisted flares is the heating value of the combustion 

zone gas. EPA’s recent settlements define combustion zone 

gas as all Vent Gas, pilot gas, and all steam just outside the 

flare tip, where combustion is supposed to take place. This 

parameter is not to be confused with the net heating value of 

Vent Gas found in current regulations which does not include 

steam or pilot gas and is measured just inside the flare. In 

the enforcement context, EPA may analyze the heating value 

of the combustion zone gas to estimate a flare’s combustion 

efficiency. A finding of low combustion efficiency is 

indicative of a potential failure to comply with the general 

duty provisions discussed above.

F e d e r a l r e q u i r e m e n t s f o r e q u i p m e n t o p e r a t o r s ’ 

general duty are found in the NSPS and NESHAP.

• “At all times, including periods of startup, shutdown, and malfunction 

...the operator shall operate and maintain any affected source, 

including associated air pollution control equipment in a manner 

consistent with safety and good air pollution control practices for 

minimizing emissions.” See, e.g., 40 CFR § 63.6(e), 40 CFR § 60.11(d).

• “Operators of control devices that are used to comply with the 

provisions of this subpart shall monitor these control devices to 

ensure that they are operated and maintained in conformance with 

their design. See, e.g., 40 CFR § 63.172(e), 40 CFR § 60.482-10.

Vent Gas is the mixture 

of gases that are to be 

combusted, usually found 

just inside the flare. The 

Vent Gas consists of 

combustible process gases, 

supplemental gas, inert 

compounds, purge/sweep 

gases, and other material.

Too much steam - 

Diluting and 

cooling the flame

Recent Flare Testing and the Net Heating Value of the 

Combustion Zone Gas.

• The net heating value in the combustion zone (NHVcz) gas 

correlates well with combustion efficiency for steam assisted 

flares. It is a better indicator of efficiency than the heating 

value of the Vent Gas alone.

• NHVcz is currently not a regulatory requirement, and is 

different from the current Vent Gas heating value minimum 

standards of 200 and 300 BTU/scf.

• NHVcz is calculated using the Vent Gas heating value, the 

flow rates of Vent Gas, steam and the pilot gas (as per recent 

settlements).

• NHVcz is closely related to another parameter, the Lower 

Flammability Limit of the Combustion Zone.

• Recent testing provides insight into NHVcz and its relationship to efficiency:

o “TCEQ 2010 Flare Study”, Texas Commission on 

Environmental Quality, August 1, 2011. 

http://www.tceq.texas.gov/assets/public/implementation/

air/rules/Flare/2010flarestudy/2010-flare-study-final-report.

pdf

o “Performance Test of a Steam-Assisted Elevated Flare 

with Passive FTIR” for Texas City and Detroit, Marathon 

Petroleum Corporation, September 2009 and July 2010. 

http://www.epa.gov/compliance/resources/publications/

civil/programs/caa/texascity-report.pdf

http://www.epa.gov/compliance/resources/publications/

civil/programs/caa/detroit-report.pdf

o “PFTIR Tests of Steam-Assisted Elevated Flares - Port 

Arthur”, Flint Hills Resources Port Arthur, LLC, June 2011. 

http://www.epa.gov/compliance/resources/publications/

civil/programs/caa/portarthur-report.pdf

Good Combustion

-Turbulent, Hot Flame Too little steam - 

Smoke due to poor 

mixing and lack 

of oxygen
Enforcement Alert

August 2012 3

Factors Affecting Flare Performance:

1. Flame Quenching in the Combustion Zone

Mixing is important because the Vent Gas and oxygen must be well mixed to complete combustion. 

Studies indicate that the assist-to-gas (steam-to-Vent Gas or air -to-Vent Gas) ratios are critical to combustion efficiency. 

Generally speaking, steam-to-Vent Gas ratios ranging between approximately 0.2 and 1.0 will result in the highest 

efficiency. Supplying a mass of air less than approximately 7 times the stoichiometric mass of air will result in the 

highest efficiencies.

Problems occur when flame quenching takes place, sometimes termed “oversteaming” or “overaeration,” which occurs at high assist-to-gas ratios. The problems occur because:

• Facilities mistakenly believe that excess steam or air will allow good combustion.

• Facilities fail to reduce steam or air when Vent Gas flow transitions from high to low. 

• Facilities have minimum steam addition rates to protect the flare tip from overheating. During low waste gas flow, 

the resulting steam-to-Vent Gas ratio can be very high, causing oversteaming. 

• The steam control equipment associated with a steam-assisted flare lacks adequate flow adjustment precision, which 

results in excess steam flow at low waste gas flow.

• The air blower associated with an air-assisted flare lacks adequate flow adjustment, which results in excess air at 

low waste gas flow.

These problems lead to significantly lower flare combustion efficiencies.

To correct these potential problems, facilities can use one or a combination of techniques, including: • Continuously measure the flow rate of the waste gas and continuously measure, and then control, the steam or air 

being added as assist gas. Follow the manufacturer’s recommendations and publicly available documents in setting 

proper assist gas rates.

• Utilize automatic damper actuators or variable frequency drives on the air supply system.

• Reduce the “minimum” or “cooling” steam rates as low as possible while still being protective of the physical 

integrity of the flare.

Factors Affecting Flare Performance:

2. Low Heat Value in Vent Gas

Vent Gas Heating Value is important because sufficient combustible material must be present to maintain flame 

stability and achieve high efficiency. 

Problems occur because facilities use flares to control waste gases that have low heating value without adding supplemental fuel to raise the Vent Gas heating value to the regulatory minimum of 200 BTU/scf or 300 BTU/

scf. See, e.g., 40 CFR 60.18(c)(3)(ii). This issue is not to be confused with NHVcz and flame quenching discussed above. Low heating value in Vent Gas occurs because:

• Facilities use flares to control a variety of streams with varying quality. When only one or a few low-flow sources 

are venting to the flare, the volumetric flow and combustible material concentrations can be minimal. 

• Batch processes are inherently variable and will have periods of very low flow or high inert (e.g., nitrogen) concentrations. Inert gas lowers the heating value of the gas mixture.

• Supplemental fuel requirements can be costly; facilities may choose not to incur that cost and will combust the 

low heating value stream alone.

• Facilities conduct compliance tests under themaximum conditions where problems with low heating values are 

unlikely. In practice, flares are not always operated at these “ideal” rates.

These problems lead to lower flare combustion efficiencies. 

To correct these potential problems, facilities can:

• Ensure that the Vent Gas meets the current regulatory heating value limits of 300 BTU/scf for assisted flares, and 

200 BTU/scf for unassisted flares, at all times. This will require evaluating the heating value of Vent Gas over the 

full range of operating scenarios.

• Determine the heating value of the Vent Gas as a whole, not only the hydrocarbons in the Vent Gas, just before it 

leaves the flare tip. The heating value evaluation includes nitrogen and any other compounds that make up the gas 

mixture that is present just inside the flare tip. 

• Monitor the Vent Gas flow and automatically supply supplemental fuel if the Vent Gas does not have sufficient 

heating value.

• Evaluate other control options and limit flare use to true emergency situations.
Marathon, BP North America, and Ongoing 

Enforcement

Two recent judicial settlements, one with the Marathon 

Petroleum Company and another with BP North America, 

include injunctive relief designed to address potential 

oversteaming issues and limit the level of future flaring. See, 

http://www.epa.gov/compliance/resources/cases/civil/caa/

marathonrefining.html and http://www.epa.gov/compliance/

resources/cases/civil/caa/bp-whiting.html. These settlements 

highlight, in addition to liability related to the general duty 

provisions discussed above, potential New Source Review 

(NSR) liability at flares. This liability stems from periods 

of low combustion efficiency that result in higher pollutant 

emissions. A source’s failure to recognize and account for 

these emissions can result in NSR violations. In addition, oil 

refiners face possible NSPS Subpart J/Ja liability because of 

the potential of burning non-compliant gas in flares. 

Flare compliance is an ongoing priority for EPA generally 

and under the Air Toxics National Enforcement Initiative

specifically. http://www.epa.gov/compliance/data/planning/

initiatives/initiatives.html#airtoxic. EPA encourages any 

company that believes it may have operated flares in a manner 

that resulted in poor combustion efficiency to expeditiously 

disclose and correct violations. 

Penalties for Violations 

Violating federal requirements for flares can result in 

a penalty, under the Clean Air Act, of up to $37,500 per 

violation, per day. To knowingly violate a flare requirement, 

including knowingly making a false or fraudulent statement 

or omiting material information required concerning a flare 

and its operation, can subject a person to criminal prosecution. 

Convictions can result in fines, imprisonment, or both. 

Conclusion

EPA Enforcement is investigating and seeking resolution 

of low heating value and excess steam or air addition at 

industrial flares. When flaring is unavoidable, Vent Gas must 

be monitored and its heating value adjusted as necessary in 

order to meet the current regulatory standards for the heating 

value of Vent Gas. Moreover, monitoring the Vent Gas and 

steam or air flow and applying steam or air and supplemental 

gas in an amount that results in high combustion efficiency 

helps assure compliance with the general duty requirements. 

Finally, flare owners are expected to operate in accordance 

with the manufacturer’s recommendations and publicly 

available documents, including the long-available literature 

from EPA, and generally available documents regarding the 

current state of scientific knowledge on flare operation and 

combustion.

Enforcement Alert

August 2012 4

Disclaimer: This document puts EPA regulatory provisions in context with plain language. Nothing in this Enforcement Alert revises or replaces any 

regulatory provisions in the Rule, any other part of the Code of Federal Regulations, the Federal Register, or the Clean Air Act. For more information 

go to: www.epa.gov/compliance. 

Well Operating Flare – High Combustion Efficiency

Poorly Operating/Over Steamed Flare - Low Combustion 

If Vent Gas is being sent to a flare but there is no visible flame, Efficiency

or if only a steam plume is visible, the flare may be operating at 

low combustion efficiency. It is better for the environment for a 

flare to produce a large orange/yellow flame than no flame at all 

when Vent Gas is present.