The procedure for using this visibility index is as follows:
1. Determine the limit of your visual range by looking for distant targets or familiar landmarks such as mountains, hills, or buildings at known distances (miles). The visual range is that point at which these targets are no longer visible.
2. 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.
3. 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 hazardous. Everyone should avoid all outdoor activities.