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Oregon Department of Environmental Quality

Air Quality

Burning and smoke

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Using visibility to estimate health effects

DEQ monitors air pollution throughout the state to ensure that air quality standards are being met. Since wildfires often occur in remote areas, air monitoring equipment may not be available. Smoke levels can rise and fall rapidly, depending on weather factors including wind direction. Making visual observations using the 5-3-1 visibility index is a simple way of estimating smoke levels and what precautions to take. While this method can be a useful tool, persons should always use caution and avoid going outside if visibility is limited, especially persons who may be sensitive to smoke. haze and smoke affects health

Estimating visibility using the 5-3-1 Index

Determine the limit of your visual range by looking for distant targets or familiar landmarks such as mountains, mesas, hills, or buildings at known distances (miles). The visual range is that point at which these targets are no longer visible.

Ideally, the viewing of any distance targets should be made with the sun behind you. Looking into the sun or at an angle increases the ability of sunlight to reflect off of the smoke, and thus making the visibility estimate less reliable.

Once distance has been determined, follow this simple guide:

    If over 15 miles
    The air quality is generally good.

    Between 5-15 miles
    Air quality is moderate and beginning to deteriorate, and is generally healthy, except possibly for smoke sensitive persons. The general public should avoid prolonged exposure if conditions are smoky to the point where visibility is closer to the 5 mile range.

    If under 5 miles
    The air quality is unhealthy for young children, adults over age 65, pregnant women, and people with heart and/or lung disease, asthma or other respiratory illness. These people should minimize outdoor activity.

    If under 3 miles
    The air quality is unhealthy for everyone. Young children, adults over age 65, pregnant women, and people with heart and/or lung disease, asthma or other respiratory illness should avoid all outdoor activities.

    If under 1 mile
    The air quality is very unhealthy, and in some cases may be hazardous. Everyone should avoid all outdoor activities.

Using the 5-3-1 Visibility Index

Distance you can see*

You are:   You have:
  • An adult

  • A teenager

  • An older child
  • Age 65 and over

  • Pregnant

  • A young child
  • OR
  • Asthma

  • Respiratory illness

  • Lung or heart disease
  • 5 miles check visibility minimize outdoor activity
    3 miles minimize outdoor activity stay inside
    1 mile stay inside stay inside

    No matter how far you can see, if you feel like you are having health effects from smoke exposure, take extra care to stay inside or get to an area with better air quality.  You should also see your doctor or other health professional as needed.

    * less reliable under high humidity conditions


    Source: Oregon Wildfire Response Protocol for Severe Smoke Episodes, version 2.0, June 3, 2014

    [print version]


    For more information about Air Quality call 503-229-5359 or email.

    Oregon Department of Environmental Quality
    Headquarters: 811 SW Sixth Ave., Portland, OR 97204-1390
    Phone: 503-229-5696 or toll free in Oregon 1-800-452-4011
    Oregon Telecommunications Relay Service: 1-800-735-2900  FAX: 503-229-6124

    The Oregon Department of Environmental Quality is a regulatory agency authorized to protect Oregon's environment by
    the State of Oregon and the Environmental Protection Agency.

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