Design Calculations of Lightning Protection Systems – Part Fourteen

In Article " Design Calculations of Lightning Protection Systems – Part Two ", I indicated the lightning protection design process involves a number of design steps as in Fig.1.

Fig.1: The Lightning Protection Design Process



Step#1: Characteristics of the Structure to Be Protected
Explained in above Article




Step#2: Risk Assessment Study



Also, In above Article, I indicated that:





Methods Of Calculations For Risk Assessment Study

The risk assessment study can be done by (4) different methods as follows:

1- Manual Method (equations and tables method),which will be explained as per:
  • IEC 62305-2,
  • NFPA780.

2-Software Method,
3- Excel Sheets Method,
4-Online Calculators Method.




First: Manual Method (Equations And Tables Method) as per IEC 62305-2




The Manual Method (Equations and Tables Method) for Calculations of Risk Assessment Study as per IEC 62305-2 can be reviewed in the following Articles:




Second: Software Method For Performing The Risk Assessment Study



S/N
Program
By
Article
1
StrikeRisk V5.0
Furse Company
2
RAPAL
Faculty of Engineering- Aristotle University of Thessaloniki
3
Riesgo
Applicationes Tecnologicas Company




Third: Excel Sheets Method For Performing The Risk Assessment Study



In Article " Design Calculations of Lightning Protection Systems – Part thirteen ", I explained two excel sheets for Need for Lightning Protection calculations as follows:

  1. IEC62305-2 Need for Lightning Protection,
  2. NFPA 780 Simplified Method.

Today, I will explain the Fourth method for performing the Risk Assessment Study: Online Calculators Method.



For more information, please review the following Articles:




Fourth: Online Calculators Method Used for Need for Lightning Protection calculations



Today, I will introduce Three Online Calculators Used to Aid in the Determination of the Need for Lightning Protection as follows:

  1. Harger’s Risk Assessment Guide,
  2. Mr. Lightning’s risk assessment program,
  3. Schirtec’s Strike risk assessment program.



1- Harger’s Risk Assessment Guide





Harger’s Risk Assessment Guide is designed to assist in determining the risk of loss due to lightning. As a guide, it is not possible to cover each special design element that may render a structure more or less susceptible to lightning damage. In these special cases it is recommended the user seek more professional advice. Personal and economic factors are very important and must be considered in addition to the assessment obtained by use of this guide.



Using Harger’s Risk Assessment Guide



To determine the need for protection against lightning for a given building or structure, the following (8) steps are to be considered:

  • Step#1: Lightning Flash Density
  • Step#2: Structures Collective Area
  • Step#3: Relative Structure Location
  • Step#4: Type of Construction
  • Step#5: Structure Contents
  • Step#6: Occupancy
  • Step#7: Lightning Consequence
  • Step#8: Submit the Information



Step#1: Lightning Flash Density
Few areas in the United States are free from thunderstorms and their attendant hazards, but some areas have more storms than others. The map shows the average lightning flash density in flashes/km2/year - for the United States. Please select the area where the structure is located.

Note: 

The Lightning Flash Density Map may vary each year and you must get the most recent one as possible for better results.




Step#2: Structures Collective Area
Select the type of structure that is relative to your circumstances and enter required values.

2.1 Rectangular structure
Enter values in (ft) for:



L=
W=
H=


2.2 Structure where a prominent part encompasses all portions of the lower part of the structure
Enter values in (ft) for:

H=
2.3 Structure where a prominent part encompasses all portions of the structure
For complex structures user enter equivalent collective area in units of square (ft) for:

Area =


Step#3: Relative Structure Location (select one)
Select relative structure location based on appropriate drawing in Step#2 from the following selections:

  • Structure located within a space containing structures or trees of the same height or taller within a distance of 3H,
  • Structure surrounded by smaller structures within a distance of 3H,
  • Isolated structure, no other structures located within a distance of 3H,
  • Isolated structure on a hilltop.


Step#4: Type of Construction
Select the Type of Construction that best describes your situation from the following selections:

4.1 Framework (select one):
  • Metal,
  • Nonmetallic,
  • Flammable,

4.2 Roof (select one):
  • Metal,
  • Nonmetallic,
  • Flammable,


Step#5: Structure Contents (select one)
Select the Type of Structure Contents that best describes your situation from the following selections:

  • Low value and nonflammable,
  • Standard value and nonflammable,
  • High value, moderate flammability,
  • Exceptional value, flammable, computer or electronics,
  • Exceptional value, irreplaceable cultural items.


Step#6: Occupancy (select one)
Select the Type of Structure Occupancy that best describes your situation from the following selections:

  • Unoccupied,
  • Normally occupied,
  • Difficult to evacuate or risk of panic.


Step#7: Lightning Consequence (select one)
Select the Type of Lightning Consequence that best describes your situation from the following selections:

  • Continuity of facility services not required, no environmental impact,
  • Continuity of facility services required, no environmental impact,
  • Consequences to the environment.

Step#8: Submit the Information
Now that you've completed all the above steps, use the "Calculate Risk" button at the bottom of the page. Your risk assessment will be calculated.



To use the Harger’s Risk Assessment Guide, click on the Link.




2-  Mr. Lightning’s Risk Assessment Program






Mr. Lightning’s Risk Assessment Program is also designed to assist in determining the risk of loss due to lightning. It looks like the Harger’s Risk Assessment Guide explained in above but with only one difference as follows:

In Step#2: Structures Collective Area, there are only two cases for the structure as follows:

  1. Rectangular structure
  2. Structure where a prominent part encompasses all portions of the lower part of the structure
While in Harger’s Risk Assessment Guide, there is a third type of structure which was a Structure where a prominent part encompasses all portions of the structure.



To use the Mr. Lightning’s Risk Assessment Program, click on the Link.




3-  Schirtec’s Strike Risk Assessment Program






Schirtec’s Strike Risk Assessment Program is based on the National Fire Protection Association (NFPA) 780 Standard and assists in determining the risk of lightning damage to particular areas and structures. In many situations the need for lightning protection is critical due to the severe consequences that could result from an unprotected lightning strike.


Using Schirtec’s Strike Risk Assessment Program


To determine the need for protection against lightning for a given building or structure, the information in the following (7) parts are to be selected/filled in:

1- Dimension of the Structure
For calculation of Equivalent Collective Area of Structure by using the entered building dimensions.


2- C1: Environmental Coefficient
It selects the Relative location of structure.


3- C2: Structural Coefficient
It selects the Type of construction materials used in the structure.


4- C3: Structure Contents
It Identifies value and flammability of contents in the structure.


5- C4: Occupancy Coefficient
It selects what is the danger to life by determining the building occupancy.


6- C5: Lightning Consequence
It identifies the Impact on environment and continuity of service.


7- Annual Average Thunder Days


It assigns Lightning Flash Density number in flashes/km2/year, choose your location on the World Flash Density Map or enter the value if known.

Note: 

The Lightning Flash Density Map may vary each year and you must get the most recent one as possible for better results.


After choosing the selections and filling in the information that best describes your circumstances. Click on the "Calculate” button at the bottom of the page. Your risk assessment will be calculated.

To use the Schirtec’s Strike Risk Assessment Program, click on the Link.


Now, we finish step#2: Risk Assessment Study from Lightning Protection Design procedure steps referred in Fig.1 in above.


In the next Article, I will continue explaining other steps of Lightning Protection Design procedure. Please, keep following.






1 comment:

  1. Schirtec's Calculator uses a different value for "tolerable frequency of property losses" than does NFPA 780 Annex L.

    ReplyDelete

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