Open burning causing excessive visible emissions is defined as opacity equal to or greater than what percentage?

• A. 20% opacity
• B. 30% opacity
• C. 50% opacity
• D. 40% opacity

Answer: (D)

Opacity is a measure of how much light is blocked by smoke in a plume. When open burning produces a plume that blocks about forty percent of the light, that is considered excessive visible emissions. This gives a clear, observable rule for deciding when a burn should be modified or stopped to reduce air pollution and protect safety. Plumes with less light blockage don’t meet the excessive-emissions criterion, while a higher threshold would allow more smoke before taking action. Forty percent provides a practical standard that is easy to apply in the field.