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 They are characterized by:
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