Chapter 3 Weather Considerations

1. Haz-Mat Incident Considerations • Chapter 3 • Weather Considerations

2. Weather Considerations • Session objectives: • The student will identify how various meteorological factors may influence a hazardous materials incident

3. Weather Considerations • Response personnel must have a basic understanding of: • daily weather patterns • irregular weather events that may occur in the area

4. Components That Affect Local Weather • Temperature • Relative humidity • Atmospheric pressure • Air density

5. Temperature • Temperature affects the following: • volatilization of a chemical from a liquid to a gas • vapor pressure • dispersion of a vapor or a gas • surface temperatures • reactivity and/or stability of a material

6. Humidity • Humidity affects vapor production from a liquid • As the humidity rises: • vaporization of water solubles will increase • vaporization of non-water solubles will decrease • Water-reactive liquids may fume vigorously

7. Precipitation • Precipitation can aggravate a haz mat incident: • may cause water-reactive chemicals to react violently • some products are designed to become activated by water • consider protective measures to maintain control of a spill during impending rain

8. Wind • Wind will affect the dispersion of a vapor or gas • Low wind vs. High wind

9. Strategic Considerations • Can evacuations be performed safely? • Will in-place protection be effective? • How large an area is affected?

10. Strategic Considerations • How much larger will the incident be when resources are in place? • How steady is the wind? • Will the wind change significantly ? • How will topographical features impact the incident?

11. Atmospheric Stability • There are two types of days: • Stable • Unstable

12. Stable Conditions • Conditions constant and unchanging • atmospheric inversion layer • smog build-up • cloud cover greater than 50% • Wind speeds are low

13. Unstable Days • Conditions are changing and variable • Characterized by: • bright sunshine • moderate afternoon winds • cumulus development if moisture is present • dust devils, straight upward movement of smoke and windy afternoons

14. Daily Wind Patterns • Winds blow up-canyon/onshore during the day • Winds blow down-canyon/offshore at night

15. Events That Cancel Daily Patterns • Gradient winds • Foehn winds • Frontal winds

16. Gradient Winds • Free-flowing prevailing winds • at an elevation where they are not influenced by topography • usually 2000 feet or more above the surface • Gradient winds are a predominant element much of the time

17. Foehn Winds • Pattern Common to California • example: Santa Ana winds • They are characterized by: • strong gusty winds • low humidity • blowing out of the east or north east • generally last 2 or 3 days

18. Frontal Winds • Associated with the passing of a major weather system • Can cause a 180 degree shift in wind direction as the front passes

19. Predicting The Effect Of Weather • Time of day the release occurs • Projected duration of the incident • Anticipated changes in the weather • Be aware of local weather patterns

20. Sources of Weather Information • Local newspaper • The National Weather Service • Municipal airports • Some fire stations • Continue to evaluate the forecast against current conditions

21. Weather Monitoring Equipment • A piece of barrier tape tied to a pole • Electronic weather equipment hooked into a computer • Assign a person the responsibility of monitoring the weather