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Low Visibility Occurrence Risk Index (LVORI)

The Low Visibility Occurrence Risk Index (LVORI) was developed based on Florida automobile accident reports when fog/smoke was a factor, and the associated weather (Lavdas and Achtemeier, 1995). It is an index for probability of low visibility, and ranges from 1 - 10, depending on relative humidity and smoke dispersion index. A 1 means there is almost no chance of low visibility, while a 10 indicates low visibility is likely. This Index is a function of relative humidity and smoke dispersion index.

From operational experience, one should be VERY CAUTIOUS ABOUT BURNING if one of the following situations occurs:

  1. When LVORI for a nighttime forecast period is 8,9 or 10
  2. When ACTIVE SMOKE from stumps logs, etc. is present during the night
  3. When there is a roadway within three miles of a burn site with open fields, logging roads, or open streams that can provide an easy transit of the smoke from the burn site to the roadway

Although not as dangerous as an index value from 8 to 10, LVORI of 6 or 7 should be treated with caution if there is active smoke produced during the night, and the burn site is near a roadway.

Table 1: Low Visibility Occurrence Risk Index (LVORI)
LVORI CategoryInterpretation
1Lowest proportion of accidents with smoke and/or fog reported (130 of 127,604 accidents, or just over 0.0010 accidents.)
2Physical or statistical reasons for not including in category 1, but proportion of accidents not significantly higher.
3Higher proportion of accidents than category 1, by about 30% to 50%, but of marginal significance (1%-5%).
4Significantly higher than category 1, by a factor of 2.
5Significantly higher than category 1, by a factor of 3 to 10.
6Significantly higher than category 1, by a factor of 10 to 20.
7Significantly higher than category 1, by a factor of 20 to 40.
8Significantly higher than category 1, by a factor of 40 to 75.
9Significantly higher than category 1, by a factor of 75 to 125.
10Significantly higher than category 1, by a factor of 150.
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This page updated: Monday, May 11, 2009 16:41