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Chapter 3Chapter 3

– Weather ConsiderationsWeather Considerations

Haz-Mat Incident Considerations

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Weather ConsiderationsWeather Considerations

Session objectives:Session objectives:– The student will identify how various The student will identify how various

meteorological factors may influence a meteorological factors may influence a hazardous materials incidenthazardous materials incident

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Weather ConsiderationsWeather Considerations

Response personnel must have a basic Response personnel must have a basic understanding of:understanding of:– daily weather patternsdaily weather patterns– irregular weather events that may occur in irregular weather events that may occur in

the areathe area

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Components That Affect Local Components That Affect Local WeatherWeather TemperatureTemperature Relative humidityRelative humidity Atmospheric pressureAtmospheric pressure Air densityAir density

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TemperatureTemperature

Temperature affects the following:Temperature affects the following:– volatilization of a chemical from a liquid to volatilization of a chemical from a liquid to

a gasa gas– vapor pressurevapor pressure– dispersion of a vapor or a gasdispersion of a vapor or a gas– surface temperaturessurface temperatures– reactivity and/or stability of a materialreactivity and/or stability of a material

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HumidityHumidity

Humidity affects vapor production from Humidity affects vapor production from a liquida liquid

As the humidity rises:As the humidity rises:– vaporization of water solubles will increasevaporization of water solubles will increase– vaporization of non-water solubles will vaporization of non-water solubles will

decreasedecrease Water-reactive liquids may fume Water-reactive liquids may fume

vigorouslyvigorously

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PrecipitationPrecipitation

Precipitation can aggravate a haz mat Precipitation can aggravate a haz mat incident:incident:– may cause water-reactive chemicals to may cause water-reactive chemicals to

react violentlyreact violently– some products are designed to become some products are designed to become

activated by water activated by water – consider protective measures to maintain consider protective measures to maintain

control of a spill during impending raincontrol of a spill during impending rain

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WindWind

Wind will affect the dispersion of a Wind will affect the dispersion of a vapor or gasvapor or gas

Low wind vs. High windLow wind vs. High wind

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Strategic ConsiderationsStrategic Considerations

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

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Strategic ConsiderationsStrategic Considerations

– How much larger will the incident be when How much larger will the incident be when resources are in place?resources are in place?

– How steady is the wind?How steady is the wind?– Will the wind change significantly ?Will the wind change significantly ?– How will topographical features impact the How will topographical features impact the

incident?incident?

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Atmospheric StabilityAtmospheric Stability

There are two types of days:There are two types of days:– StableStable– UnstableUnstable

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Stable ConditionsStable Conditions

Conditions constant and unchangingConditions constant and unchanging– atmospheric inversion layer atmospheric inversion layer – smog build-upsmog build-up– cloud cover greater than 50%cloud cover greater than 50%

Wind speeds are lowWind speeds are low

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Unstable DaysUnstable Days Conditions are changing and variableConditions are changing and variable Characterized by: Characterized by:

– bright sunshinebright sunshine– moderate afternoon windsmoderate afternoon winds– cumulus development if moisture is cumulus development if moisture is

presentpresent– dust devils, straight upward movement of dust devils, straight upward movement of

smoke and windy afternoonssmoke and windy afternoons

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Daily Wind PatternsDaily Wind Patterns

Winds blow up-canyon/onshore during Winds blow up-canyon/onshore during the daythe day

Winds blow down-canyon/offshore at Winds blow down-canyon/offshore at nightnight

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Events That Cancel Daily Events That Cancel Daily PatternsPatterns Gradient windsGradient winds Foehn windsFoehn winds Frontal windsFrontal winds

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Gradient WindsGradient Winds

Free-flowing prevailing windsFree-flowing prevailing winds– at an elevation where they are not at an elevation where they are not

influenced by topographyinfluenced by topography– usually 2000 feet or more above the usually 2000 feet or more above the

surfacesurface– Gradient winds are a predominant element Gradient winds are a predominant element

much of the timemuch of the time

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Foehn WindsFoehn Winds

Pattern Common to CaliforniaPattern Common to California» example: Santa Ana windsexample: Santa Ana winds

They are characterized by:They are characterized by:– strong gusty windsstrong gusty winds– low humiditylow humidity– blowing out of the east or north eastblowing out of the east or north east– generally last 2 or 3 daysgenerally last 2 or 3 days

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Frontal WindsFrontal Winds

Associated with the passing of a major Associated with the passing of a major weather systemweather system

Can cause a 180 degree shift in wind Can cause a 180 degree shift in wind direction as the front passesdirection as the front passes

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Predicting The Effect Of WeatherPredicting The Effect Of Weather

Time of day the release occursTime of day the release occurs Projected duration of the incidentProjected duration of the incident Anticipated changes in the weatherAnticipated changes in the weather Be aware of local weather patternsBe aware of local weather patterns

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Sources of Weather InformationSources of Weather Information

Local newspaperLocal newspaper The National Weather ServiceThe National Weather Service Municipal airportsMunicipal airports Some fire stationsSome fire stations Continue to evaluate the forecast Continue to evaluate the forecast

against current conditionsagainst current conditions

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Weather Monitoring EquipmentWeather Monitoring Equipment

A piece of barrier tape tied to a poleA piece of barrier tape tied to a pole Electronic weather equipment hooked Electronic weather equipment hooked

into a computerinto a computer Assign a person the responsibility of Assign a person the responsibility of

monitoring the weathermonitoring the weather