United States Environmental Protection Agency Region 10

April 2005



Fact Sheet

Rule for Limiting Visible Emissions

(40 Code of Federal Regulations Part 49 Section 124)

Federal Air Rules for Indian Reservations
in Idaho, Oregon, and Washington

What is the FARR? The Federal Air Rules for
Indian Reservations in Idaho, Oregon, and
Washington, also called the FARR, is a set of air
quality regulations established under the Clean
Air Act. The FARR creates rules to manage
activities that cause air pollution.

The FARR applies to all residents (both tribal
members and non-tribal members) and
businesses located within the exterior boundaries
of reservations in Idaho, Oregon, and
Washington. The ownership status of land on the
reservation does not affect how the rules apply.

What will the FARR do? The FARR will protect
human health and the environment for 200,000
people on reservations in the Pacific Northwest.
The FARR will also:

•	Establish federal air quality rules where EPA-
approved state or tribal air quality programs do
not exist

•	Make air quality standards on reservations
consistent with standards off of reservations

•	Build capacity for tribes to develop tribal air
programs.

Fact Sheet Series

The FARR includes 16 rules that address various
air quality issues:

49.122 Partial Delegation of Administrative
Authority to a Tribe

49.124	Visible Emissions

49.125	Particulate Matter

49.126	Fugitive Particulate Matter

49.127	Woodwaste Burners

49.128	Particulate Matter Emissions from Wood
Products Industry Sources

49.129	Sulfur Dioxide

49.130	Sulfur Content of Fuels

49.131	Open Burning

49.132	General Open Burning Permits

49.133	Agricultural Burning Permits

49.134	Forestry and Silvicultural Burning Permits

49.135	Emissions Detrimental to Public Health
or Welfare

49.136	[Reserved]

49.137	Air Pollution Episodes

49.138	Registration of Air Pollution Sources and
Report of Emissions

49.139	Rule for Non-Title V Operating Permits

What is the purpose of this rule?

The purpose of the Rule for Limiting Visible Emissions is to set
limits for visible emissions produced by certain air pollution sources that
operate within an Indian reservation. Visible emissions occur when
particulate matter is present in an amount large enough to be seen by the
human eye. Visible emissions include particulate matter. Particulate
matter is a mixture of solid particles and liquid droplets that is in the air.
Meeting these limits will help make certain that emissions of particulate
matter are reduced and that pollution controls and process equipment are
maintained and operated properly.

Why is this rule important?

High levels of visible emissions mean that air pollution sources are
being managed and controlled poorly. These high levels can affect
human health and public safety. High levels of particulate matter
emissions can affect human health by increasing cases of respiratory
disease such as asthma and respiratory infection. Public safety can be
affected in cases where extremely high levels of visible emissions may
block the sight of motorists and equipment operators.

To whom does this rule apply?

This rule is for each of the 39 Indian reservations in Idaho, Oregon,
and Washington specified in the FARR. The rule applies to anyone who
owns or operates an air pollution source that produces particulate matter
or other visible air emissions.

This rule does not apply to:

•	Open burning.

•	Agricultural activities.

•	Forestry and silvicultural activities.

•	Non-commercial smokehouses.

•	Sweat houses or lodges.

•	Smudge pots.

•	Furnaces and boilers that are used only to heat residential buildings
that have four or fewer apartments or housing units.

•	Fugitive dust from roads owned or maintained by any federal, tribal,
state, or local government. (Fugitive dust is particulate matter
released into the air by wind or other similar forces.)

•	Emissions from burning fuel in mobile sources, such as motor
vehicles, non-road vehicles and engines, locomotives, and marine
(water) vehicles.


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Fact Sheet-Rule for Limiting Visible Emissions

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What are the requirements of this rule?

This rule sets limits on visible emissions. The rule
also describes certain cases when an air pollution source
can exceed these limits. Finally, this rule specifies the
methods that an air pollution source can use to show that
the visible emissions limits are being met.

The limit on visible emissions is 20 percent opacity
over any consecutive 6 minute period. Percent opacity is
the percentage of a background scene that an air pollution
source blocks. A plume of smoke or dust from a chimney
or pipe is an example of an air pollution source. Zero
percent opacity would be a clear plume that does not block
any of the background scene. One hundred percent opacity
would be a plume that blocks the background scene
completely.

The rule allows two exceptions to the 20 percent
opacity limit:

•	Exception 1. The limit may be exceeded if the only
reason that the limit cannot be met is because of the
presence of water or steam in the visible emissions.

•	Exception 2. The visible emissions from an oil-fired
or solid fuel-fired boiler that continuously measures
opacity with a continuous opacity monitoring system,
also called COMS, can exceed the 20 percent opacity
limit during start-up, soot blowing, and grate cleaning.
This limit can be exceeded for a single time period of
up to 15 consecutive minutes in any 8 consecutive
hours. However, the opacity cannot exceed 60 percent
at any time.

The rule allows two ways, also called reference
methods, for the owners or operators of air pollution
sources to determine whether the visible emissions limit is
being met. The first reference method for determining
opacity is called EPA Reference Method 9. This method is
described in 40 Code of Federal Regulations (CFR)

Part 60 Appendix A. The second, or alternative, reference
method for determining opacity is the use of a COMS. The
COMS must comply with Performance Specification 1
found in 40 CFR Part 60 Appendix B.

When does this rule take effect?

This rule is effective June 7, 2005. The final rule was
published in the Federal Register on April 8, 2005 (67 FR
18074).


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