03-1 n Chapter 3 –Weather Considerations Haz-Mat Incident Considerations

03-2 Weather Considerations n Session objectives: –The student will identify how various meteorological factors may influence a hazardous materials incident

03-3 Weather Considerations n Response personnel must have a basic understanding of: –daily weather patterns –irregular weather events that may occur in the area

03-4 Components That Affect Local Weather n Temperature n Relative humidity n Atmospheric pressure n Air density

03-5 Temperature n 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

03-6 Humidity n Humidity affects vapor production from a liquid n As the humidity rises: –vaporization of water solubles will increase –vaporization of non-water solubles will decrease n Water-reactive liquids may fume vigorously

03-7 Precipitation n 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

03-8 Wind n Wind will affect the dispersion of a vapor or gas n Low wind vs. High wind

03-9 Strategic Considerations –Can evacuations be performed safely? –Will in-place protection be effective? –How large an area is affected?

03-10 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?

03-11 Atmospheric Stability n There are two types of days: –Stable –Unstable

03-12 Stable Conditions n Conditions constant and unchanging –atmospheric inversion layer –smog build-up –cloud cover greater than 50% n Wind speeds are low

03-13 Unstable Days n Conditions are changing and variable n Characterized by: –bright sunshine –moderate afternoon winds –cumulus development if moisture is present –dust devils, straight upward movement of smoke and windy afternoons

03-14 Daily Wind Patterns n Winds blow up-canyon/onshore during the day n Winds blow down-canyon/offshore at night

03-15 Events That Cancel Daily Patterns n Gradient winds n Foehn winds n Frontal winds

03-16 Gradient Winds n 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

03-17 Foehn Winds n Pattern Common to California »example: Santa Ana winds n They are characterized by: –strong gusty winds –low humidity –blowing out of the east or north east –generally last 2 or 3 days

03-18 Frontal Winds n Associated with the passing of a major weather system n Can cause a 180 degree shift in wind direction as the front passes

03-19 Predicting The Effect Of Weather n Time of day the release occurs n Projected duration of the incident n Anticipated changes in the weather n Be aware of local weather patterns

03-20 Sources of Weather Information n Local newspaper n The National Weather Service n Municipal airports n Some fire stations n Continue to evaluate the forecast against current conditions

03-21 Weather Monitoring Equipment n A piece of barrier tape tied to a pole n Electronic weather equipment hooked into a computer n Assign a person the responsibility of monitoring the weather