Laserfiche WebLink
2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan <br />Volume 2 — Hazard Inventory <br />4 1#""';' Hazard Assessment: VOLCANIC ASH <br />4.1.4.1. Definition. <br />Volcanic ash consists of tiny particles of jagged rock and <br />natural glass blasted into the air by a volcano. This ash <br />poses threats to human and animal health, aircraft <br />engines, electronics, machinery, electrical power <br />generation and telecommunications. Winds may carry <br />ash thousands of miles, impacting areas and people far <br />away from the volcano itself. Volcanic ash is not the <br />product of combustion, and thus is not like the light ashes <br />made by burning leaves, wood, or coal, for example. <br />Volcanic ash particles are hard rock fragments that do not <br />dissolve in water. Ash is extremely abrasive, mildly <br />corrosive and can conduct electricity when wet. <br />4.1.4.2. Range of magnitude <br />Unknown, pending conclusion of the Hennepin County Emergency Management assessment in 2020. <br />4.1.4.3. Spectrum of Consequences B2b <br />4.1.4.3.1. PRIMARY CONSEQUENCES <br />4.1.4.3.1.1. Aircraft. Aircraft in flight are particularly vulnerable to the effects of exposure <br />to volcanic ash. Often the ash cloud is invisible to the flight crew, and must be detected <br />by the odor of sulfur, or by a haze developing on the windscreen. The electrically charged <br />ash particles can interfere with navigational and flight instruments, and communications <br />equipment. The ash may clog the pitot-static system that indicates airspeed and feeds air <br />to several vital flight instruments. Abrasion by the jagged particles can erode leading edge <br />surfaces, and quickly produce a haze on windscreens so that pilots are unable to see <br />through them. Turbine compressor blades in jet engines can wear quickly. Finally, the low <br />melting temperature of volcanic ash means that the particles liquefy in the ignition <br />chamber of jet engines, but quickly cool in the next engine stage and end up coating <br />engine parts with a glaze of volcanic glass. Engines have failed from ingesting volcanic <br />ash. Repair costs from encounters with ash can cost millions of dollars per aircraft. <br />4.1.4.3.1.2. Surface transportation. At the surface, ash fall could produce hazardous <br />driving conditions by cutting visibilities when at least 1 millimeter (1/32 inch) of ash <br />accumulates on roadways. Ash fall amounts of accumulation greater than 1 mm (1/32 <br />Inch) also obscure markings on roadways, causing confusion among drivers in the low <br />visibility conditions. <br />4.1.4.3.1.3. Human health. The main health impact of volcanic ash to people (and <br />animals) are to the respiratory tract and to the eyes. Ash particles less than 100 <br />nanometers in size produce upper airway irritation. Ash particles less than 10 <br />nanometers in size can penetrate deep into the lung and worsen the conditions of those <br />29 <br />