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Harger Lightning & Grounding © 2005

Harger Lightning & GroundingHarger Lightning & Grounding20052005

Lightning Protection SystemsLightning Protection Systems



Lightning Protection Systems

I. What is Lightning/Lightning Protection?II. Basic Principles of Lightning ProtectionIII. Risk AssessmentIV. Applicable Codes/Standards V. Basic ComponentsVI. “ Typical ” Roof Top Detail


I. What is Lightning?

Consider Lightning a Gigantic Electrical Spark traveling betweenConsider Lightning a Gigantic Electrical Spark traveling betweenCloud to Cloud or Cloud to Earth containing an average Charge ofCloud to Cloud or Cloud to Earth containing an average Charge of30 to 50 Million Volts and a Current of 18,000 Amps.30 to 50 Million Volts and a Current of 18,000 Amps.



What is Lightning Protection?

NFPA 780 -

A Complete System of Air Terminals, Conductors, Ground Terminals, Interconnecting Conductors, Surge Suppression Devices, and other Connectors or Fittings required to complete the System.


Lightning Damage Can Be Traced To :

Inadequate (or no) direct strike protection


Risks Posed from a Direct StrikeRisks Posed from a Direct Strike


Risks Posed from an Indirect StrikeRisks Posed from an Indirect Strike



What is notnot Lightning Protection?

Early Streamer Emission – ESERadioactivePulsed VoltageSparking – Controlled Leader Trigger (CLT)

Lightning EliminationDissipation Array Systems (DAS)Charge Transfer Systems (CTS)



ESE – Early Streamer EmissionManufacturers claim that the ESE launch an upward streamer faster than conventional Franklin Rods or the features on the structures to be protected.Claim streamer speeds of 106 m/s to provide this advantageActual field measures from multiple investigators have documented streamer speeds ranging from

McEachron - 5.2 x 104 to 6.4 x 105 m/sYokoyama - 0.8 to 2.7 x 105 m/s

Laboratory propagation speeds 104 m/sStriking distance directly proportional to Leader charge.

Reference: M.A. Uman & V.A Rakov (University of Florida)American Meteorological Society Paper 2002



ESE – Early Streamer EmissionHeary Bros – PreventorIndelec - PrevectronErico – DynasphereFranklin France – Saint ElmoIngescoDuval Messien – SatelitHelita

1999 Byran Report commissioned by NFPA – found no technical basis for the claims of enhanced performance


Prevectron

Dynasphere

19mm Blunt Franklin Rod

Seven year period - air terminals on 6 m mastsNeither ESE or Sharp Franklin Rods struck12 Blunt Franklin Rods were struck (12.7 to 25.4 mm)

Charles Moore - Principal Investigator - New Mexico Tech


French Made - Duval Messien SatelitESE 30m from damaged wall

Photos courtesy Hartono & Robiah

Malaysia Apartment Building

One of numerous such cases in Malaysia where ESE have failed to protect structures where the ESE was located at a distance well within the claimed radius of protection.



High Voltage Lab Test

Mississippi State University


Dynasphere Damaged


ESE LawsuitIn connection with the NFPA’s rejection of ESE draft standard 781, three ESE companies (Heary Bros. Lightning Protection Co., Inc., Lightning Preventor of America, Inc., and the National Lightning Protection Corp., of which the two first mentioned have merged) filed a law suit against the Lightning Protection Institute, Thompson Lightning Protection Inc., and East Coast Lightning Equipment, Inc.

The lawsuit, which was initiated in 1996, contained allegations of conspiracy, false advertising and product defamation regarding the advertised improved efficiency of ESE terminals compared to conventional Franklin rods.

In October, 2003, the Federal District Court of Arizona dismissed the lawsuit.The dismissal was largely based on the fact that the ESE vendors presented no admissible evidence at all to support their claims. Additionally, the Court granted a favorable ruling to a counterclaim against the ESE vendors. The ESE vendors were convicted of falsely advertising the claimed increase in efficiency of ESE rods in comparison to conventional Franklin rods.

Significantly, the verdict rejected the ESE vendor’s claims that their ESE terminals’compliance with various ESE standards justified the advertised expanded zones of protection for ESE devices. The Court found that the conformance with foreign ESE standards failed to prove claimed increased zones of protection for ESE rods. The Court found that the ESE vendor’s claims are not supported by tests sufficiently reliable to support those claims and are therefore in violation of American “truth-in-advertising”laws.



Lightning Elimination

According to proponents the charge released via corona discharge at the sharp points will either:

1. Discharge the overhead thundercloud thereby eliminating any possibility of lightning (Dissipation Array)

2. Discourage a downward-moving leader from attaching to the array or structure by reducing the electric field near the arrayand, hence, suppress the initiation of an upward streamer.



Dissipation / Charge Transfer System)SplineballLightning MasterLEC – Dissipation Array System DASLEC – Charge Transfer System CTSLightning Prevention Systems – ALS Static Dissipater


What is notnot Lightning Protection?Lightning EliminationDevices have failed to perform as claimed by manufacturers.

US Federal Aviation Administration (FAA)• Banned after towers and DAS struck

National Aeronautical Space Administration• Banned after towers struck at Kennedy Space Center

US Military• Banned towers at military bases struck

Japan - field test showed statistical distribution of peak current unchanged. (Kuwabara et al.)Trees & grass often generate more corona discharge than dissipation arrays without apparently inhibiting lightning.


Non Conventional Lightning Protection Systems

These systems are not allowed by:US National Fire Protection Association (NFPA)IEEEIECUS MilitaryUnderwriters Laboratory (UL)


II. Basic Principles of Lightning Protection

• Intercept the Lightning Discharge• Safely Conduct the Lightning Currents• Minimize the Effects of Lightning Currents• Dissipate the Lightning Currents in the Earth

Zone of Protection - space adjacent to LPS substantially immune to direct lightning discharges. Determined using Rolling Sphere Method.


III. Risk Assessment*

The Lightning Risk Assessment Methodology is provided to assist the building owner or architect/engineer in determining the risk of damage due to lightning. The methodology considers only the damage caused by a direct strike to the structure.

* NFPA 780 revised in 2004


Lightning Strike Probability

The probability that a structure will be struck by lightning is the product of the equivalent collection area of the structure times the flash density for the area that the structure is located.


Risk Assessment Formula

If Nd > Nc Lightning Protection Should be Installed

Nd = The Yearly Lightning Strike Frequency

Nc = Tolerable Lightning Frequency



Nd = (Ng)(Ag)(C1)Where:

Ng = The yearly average flash density in the region where the structure is located.

Ag = The equivalent collective area of the structure in km2.

C1 = The environmental coefficient.


10-year Flash Density Map - U.S.

)

0.1

0.5

1.0

2.0

3.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

Ng = The Yearly Average Flash Density

Units: flashes/km2/yr

Lightning Density Map provided by Global Atmospherics, Inc. Tucson Arizona.


Ag = The Equivalent Collective Area

Refers to the ground area having the same yearly direct lighting flash probability as the structure. It is an increase area for the structure that includes the effect of the height and location of the structure.There are 3 models:


Rectangular Model


Model 2


Model 3



C1 = The Environmental Coefficient

The Environmental Coefficient accounts for the topography of the site of the structure and any object located with the distance 3H from the structure that can affect the collection area.They are as follows:


C1 = The Environmental Coefficient

Relative Structure Location C1Structure located within a space containing structures or trees of the same height or taller with a distance of 3H

0.25

Structure surrounded by smaller structures within a distance of 3H

0.5

Isolated structure, no other structures located with a distance of 3H

1

Isolated structure on a hilltop 2


Tolerable Lightning Frequency (Nc)

The Tolerable Lightning Frequency is a measure of the damage risk to the structure including factors affecting risks to the structure, environment and monetary loss. It is calculated as follows:


Tolerable Lightning Frequency (Nc)

Nc = 1.5 x 10-3

CWhere:

C = (C2)(C3)(C4)(C5)


C2 – Structural CoefficientRoof

Structure Metal Nonmetallic Flammable

Metal 0.5 1.0 2.0

Nonmetallic 1.0 1.0 2.5

Flammable 2.0 2.5 3.0


C3 – Structural Contents Coefficient

Structure Contents C3

Low value and nonflammable 0.5

Standard value and nonflammable 1.0

High value, moderate flammability 2.0

Exceptional value, flammable, computer or electronics

3.0

Exceptional value, irreplaceable cultural items 4.0


C4 – Structural Occupancy Coefficient

Structure Occupancy C4Unoccupied 0.5Normally occupied 1.0Difficult to evacuate or risk of panic 3.0


C5 – Lightning Consequence Coefficient

Lightning Consequence C5

Continuity of facility service not required, no environmental impact

1.0

Continuity of facility service required, no environmental impact

5.0

Consequences to the environment 10.0


Risk Assessment Formula

If Nd > Nc Lightning Protection Should be Installed


Nc = Tolerable Lightning Frequency

Lightning Risk Assessment for Rectangular Structure

Lightning Flash Density (Fig. H.2) …………………… Ng = 4

Relative Structure Location (Table H.4.3) …………… C1 = 2

Rectangular Structure Length (ft) : L = 80 ftWidth (ft) : W = 50 ftHeight (ft) : H = 30 ft

Equivalent Collective Area: Ae = 4.91E-03 km 2̂

Lightning Strike Frequency: Nd = 3.93E-02

Structural Coefficients (Table H.5.a) ………………… C2 = 3Structural Contents Coefficients (Table H.5.b) ……… C3 = 3Structural Occupancy Coefficient (Table H.5.c) …… C4 = 1Lightning Consequence Coefficient (Table H.5.d) …… C5 = 5

Tolerable Lightning Frequency: Nc = 3.33E-05

Lightning Protection System Should Be Installed

Based on NFPA780-2000

Rectangular Model

Example


IV. Applicable Codes/Standards

NFPA 780UL 96AUL 96


NFPA 780

• Standard for the Installation of Lightning Protection Systems (2004)

• Most Active Standard Available• Not a Code, (not enforced)


UL 96 & 96A

• 96A - Installation Standard• “Master Label”• Independent Third Party Testing• 96 - Manufacturing Standard for Listed

LP Components


UL Master Label Program

Must be UL Listed to be Eligible

Materials must be UL Listed

System will be subjected to Inspection by UL


VII. Basic Components

• Air Terminals• Lightning Conductors• Ground Terminals• Connectors/Fittings• Surge Suppression Devices


Types of Air Terminals

• Plain Air Terminals• Safety Air Terminals• Flexible Air Terminals


New Mexico Tests

19mm (3/4”) blunt rod was most effective


Types of Lightning Conductors

• UL Listed Lightning Conductors

• Copper • Aluminum

• Class I • Class II

• Structural Steel Framework


Types of Ground Terminals

• Ground Rods

• Plain/Sectional Copper-Clad Steel, Copper, Galvanized Steel, Stainless Steel

• Enhanced Ground Rods


Types of Ground TerminalsContinued...

• Ground Plates• Ground Mesh• Concrete Encased

Electrodes• Reinforcing Steel• Copper Conductors


Connectors/FittingsFunctions

• Bonds Conductors to Strike Terminals and Ground Terminals

• Bond Metal Bodies to Provide a Path to Ground

• Alleviates Potential Differences between System and Metal Bodies

• Helps Prevent Flashover Potentials


Surge Suppression DevicesHelps Prevent Surge Currents from Entering the Structure via Electrical, Data, Phone, Cable Lines, etc.

Integral Part of Total Protection Package

UL96A & NFPA Surge Suppression Requirements vague

Roof Top Detail

VIII.


Details

Thank You


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