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