Haz-Mat Incident Considerations Chapter 3 Weather Considerations

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

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

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

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

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

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

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

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

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?

Atmospheric Stability There are two types of days: Stable Unstable

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

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

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

Events That Cancel Daily Patterns Gradient winds Foehn winds Frontal winds

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

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

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

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

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

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