Using visibility to estimate health effects during a wildfire

(from DEQ's website: http://www.deq.state.or.us/aq/burning/wildfires/visibility.htm)

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.

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