11.8 electric discharge

11.8

Charges and the Earth

Charges and the Earth

• Any conductor in contact with the

earth is said to be GROUNDED and

What causes lightning

?

• Lightning is actually

just static electricity

on a much larger

scale.

• The rubbing is

caused by air moving

around

Lightning

Lightning

• The negative charges can discharge

inside the cloud

Lightning

Science@NASA :

science.nasa.gov/.../y2006/13sep_electr icice.htm 2006

The nagative charges can

also discharge to the ground

below. (Current) This is

what happens when

Thunder

• When the lightning flash happens it heats

the air to a temperature 5 times hotter than

the surface of the sun.

• This causes an explosive expansion and

vibration of nearby air

Discovery Wonders of Weather:

Lightning Phenomena

http://videos.howstuffworks.com/di

scovery/406-discovery-wonders-of-

Facts about Lightning

• A strike can average

100 million volts

of

electricity

• Current of up to

100,000 amperes

• Can generate

54,000

F

• Lightning strikes somewhere on the Earth

every second

What Does This Mean?

• Lightning can strike ground up to ten

miles from a storm (

Lightning out of

the blue

)

• There is an average of

2-3 miles

Use The Five Second Rule

• Light travels at about 186,291

miles

/second

• Sound travels at only 1,088

feet

/second

• You will see the flash of lightning almost

immediately

• 5280/1088= 4.9

Four Main Features of Lightning

Protection

• 1) Air terminal

• 2) Conductors

• 3) Ground termination

Air Terminal and Conductors

Grounding Rod

Overview

•

LIGHTNING -- SIGNIFICANT HAZARD!

•

Lightning -- Significant Hazard

• LIGHTNING: The Underrated Weather Hazard!

• #2 Storm Killer In U.S.

• More Than Tornadoes And Hurricanes Combined

• Life-Long Debilitating Injury On Many More Than It Kills

• Kills ~10 / Year And

Injures ~ 100 to 150 / Year In Canada

• $5 Billion Economic Impact Each Year In U.S.

Lightning Casualties In U.S. (1959-1994)

(National Severe Storms Laboratory)

Radio and Radio Equipment

(1%) Farm and Heavy Equipment (5%) Telephone (4%) Golf (6%) Open Fields

(Includes Sports Fields)

(45%) Under Trees (23%) Water (Swimming, boating, fishing) (14%)

Golf and Trees

(2%)

Activities Put peopleAt High Risk!

Activities that Put You At High Risk!

• Open Fields (45%)

• Sports Fields

• Playgrounds

• Recess Outdoors

• Marching Band

• Extra Concerns:

• Metal Bleachers!

• Long Metal Fences!

• Playground Equipment

• Under Trees (23%)

• Potentially Any Outdoor Activity

Activities that Put You At High Risk!

• Water Related (14%)

• Swimming

• Indoor Pools Too! • Boating

Activities That Put You At High Risk!

• Golf (6%)

• Golf Teams

• Heavy Equipment (5%)

• Grounds Keepers

• Telephone (4%)

• Everyone!

Activities That Put you At High Risk!

NO!

• Don’t “Tough It Out”!

• Do Postpone Or Cancel Event

• Children’s Lives And

Life-Long Crippling Injuries More Important Than A Game!

• Sports Have Fastest Rising Lightning Casualty Rate

Activities That Put you At High Risk!

‘LSG’ Recommendations

(con’t.)

Recommendations

(con’t.)

30

30

30

30

• Use ‘30-30 Rule’ To Determine If Lightning Is A Threat

• If 30 Secs Or Less “Flash To Bang”, Seek Proper Shelter • Back-Up Rule (if you can’t see the lightning):

If You Can Hear Thunder, Seek Proper Shelter • Wait 30 Min Or More After Last Thunder,

Before Leaving Proper Shelter

• Most Casualties Occur Before, And Especially After, Thunderstorms

• 30-30 Rule May Seem Too Conservative -- It’s Not!

‘LSG’ Recommendations

(con’t.)

30

30

Most Important Points

• People Don’t Realize The Long Distances Lightning Can Strike

• Average 3 NM Between Strikes

• ‘Bolt From The Blue’ ~15 NM Not Uncommon

• Ground Strike ~60 NM Documented From Anvil (Rare Distance)

• People Don’t Realize The Long Times Lightning Can Strike After The Thunderstorm Has Decayed

Recommendations

(con’t.)

Seek Proper Shelter

• Buildings Much Better Than Vehicles

• Vehicles Offer Some Safety

• No Place Outside Is Safe Near A Thunderstorm

• Near  6 Miles 10 9 8 7 6 5 4 3 2 1 0

Lightning Certified Facility

Outdoors

Lightning Protected Building

Re la tive L ig htn in g Prote ction

• Once In Proper Shelter, Avoid Conducting Paths To Outside • Telephone (corded)

• Electrical Appliances / Wiring • TVs, VCRs, And TV Cables • Computers

• Light Switches • Electrical Outlets • Plumbing

• Showers • Sinks

• Rest Rooms

• Pools (indoors too) • Don’t Watch Lightning

From Windows / Doorways • Inner Rooms Are Better

Recommendations

(con’t.)

Summary

• Lightning Is Extremely Significant Hazard, But Far Too Often Underrated

• Lightning Safety Group Recommendations

Can Help Schools Improve Their Lightning Safety

• Schools Must Play A Vital Role! • Lightning Safety Plan

•Credits

• William P. Roeder

• [email protected]

• (321) 853-8410, DSN 467-8410

• https://www.patrick.af.mil/45og/45ws/