Lightning Risk Assessments
All areas on the Earth’s surface are at some level of risk of damage from a lightning strike. Similarly, objects above and below the surface are at risk as well. No one can determine when lightning will strike, where it will strike or the paths lightning currents take. Lightning current can flow through the air, wood, concrete and soil among many other obvious conductors. Lightning currents can reach millions of amps.
Understanding the risks associated with damage to a facility, piece of equipment and other conductive objects is part of managing power quality. Building structures, whether above or below ground—one floor or level or 20 stories above ground, are the primary building structures of concern with respect to damage caused by lightning. Structures also include conductive objects like utility transmission towers, above ground utility power distribution systems and cellular towers, for example. The level of risk depends on many factors. Factors include the geographical region where the facility is located, the construction of the facility and whether or not there are any existing lightning protection devices installed such as surge protectors and grounding electrodes.
If an unprotected facility is struck by lightning, the lightning can travel through the walls instantly turning any moisture into steam which may result in a high pressure explosions of concrete walls. Loss of service and injury to personnel are also a high risk factor. An unprotected facility or property can increase exposure of people working in and around a facility; the facility itself including its construction—building materials and critical infrastructures—electrical, plumbing, HVAC, etc.; electrical and electronic equipment installed in a facility or on a property.
Facilities which have experienced lightning damage should contact Electrotek to discuss the lightning event and the damaged it caused. Expert lightning assessment engineers at Electrotek have the expertise to evaluate facilities and equipment struck by lightning, conduct a detailed lightning assessment and provide custom engineering designs for lightning protection systems (LPS) for all types of facilities—residential, commercial and industrial: indoor and outdoor. In laymen’s terms, one objective of an LPS is to steer lightning currents away from objects that can suffer damage caused by the high currents.
A lightning protection system is designed to protect a structure from damage due to lightning strikes. The objective of an LPS is to intercept such strikes and safely provide a path easiest for the extremely high lightning currents to flow to ground. An LPS includes a network of air terminals, bonding conductors, and ground electrodes designed to provide a low impedance path to ground for potential strikes.
Comprehensive Lightning Risk Assessments
Electrotek expert lightning engineers can provide comprehensive lightning risk assessments and lightning protection designs to help ensure that a lightning strike will not cause catastrophic failures of facilities and equipment, and injuries or fatalities at facilities. Electrotek’s lightning risk assessment and proposed lightning protection designs illustrate the current risks and necessary steps that should be taken in order to meet the guidelines as set out in NFPA 780-2017 - Standard for the Installation of Lightning Protection Systems and IEEE 998-2012 - IEEE Guide for Direct Lightning Stroke Shielding of Substations.
NFPA 780-2017 provides installation requirements for lightning protection systems to safeguard people and property from fire risk and related hazards associated with lightning exposure. While NFPA 780-2017 is not enforceable by law, it is generally recognized as the primary lightning protection document in the United States. The purpose of NFPA 780-2017 is to safeguard persons and property from lightning.
NFPA 780-2017 has two risk assessments: a simplified version and a detailed version. The simplified verson tells you if your site needs a lightning protection system, while the detailed tells you if a partial lightning protection system will work, or if you need a full system. Electrotek typically runs both versions in order to determine where cost savings can be made.
Improved Lightning Flash Density Forecasts
Few areas are free from thunderstorms and the hazard of a lightning strike, but some areas have more storms than others. In fact, thunderstorm activity in the United States is increasing (www.ncdc.noaa.gov). The higher the lightning flash density (or ground flash density), the higher the probability of a lightning strike at your facility which will require a higher level of lightning protection.
Determining the lightning flash density at a given facility location is critical to a lighting risk assessment and to managing power quality inside / outside of a facility and at a site. IEEE 998-2012 estimates lightning flash density based on average number of thunderstorm days or ‘keraunic’ level. NFPA 780-2017 uses the default national flash density map with data from 1997 to 2010. Electrotek can provide an improved a report containing up-to-date lighting flash data gathered from the National Oceanic and Atmospheric Association Severe Weather Data (NOAA) (see https://gcmd.nasa.gov/records/GCMD_NLDN.html) specifically for the precise plot of land where a facility or equipment farm is located. This allows for calculating much more accurate future predictions.
Assessing the Risk of a Lightning Strike
Performing a lightning risk assessment to determine if a facility needs a lightning protection system requires an Electrotek lightning engineer to evaluate environmental factors and tolerable risk factors. Calculations are performed to determine if a lightning protection system with surge protection devices (SPDs) is required to manage the risks of facility and equipment damage.
Electrotek’s lightning strike risk assessments are calculated using several environmental factors including:
- Characteristics of buildings and equipment such as: building construction, equipment costs, ability to withstand voltage, flammable materials, cable and wiring layouts.
- Existing lightning protection measures such as: surge protection, shielding, grounding electrodes and lightning rods.
The following risks are also factored into the calculations:
- Risk associated with fire.
- Risk associated with loss of life or injury.
- Risk associated with loss of service—utility power and communications.
- Risk associated with loss of equipment.
Based on an analysis of all of the above factors, a detailed lightning risk assessment and lightning protection plan is developed for one or more facilities and for the site as a whole, if required. The objective is to achieve an acceptable risk level with the proposed lightning protection system according to NFPA 780-2017.
Electrotek's Lightning Risk Assessment Process
Electrotek’s lightning strike risk assessment process typically follows these steps:
- NFPA 780-2017 lightning risk assessment – This assessment uses a variety of environmental and engineering factors to determine two variables:
- Does the facility or site require a lightning protection system?
- If so, what level of protection is required?
- There are four lightning protection levels: Level I through IV with I having the highest level of protection.
- IEEE 998-2012 lightning strike shielding analysis – This assessment analyzes the lightning protection system to be installed at the site and its capacity to handle lighting strikes along with other important data.
- The following steps are required to conduct a IEEE 998-2012 lightning risk assessment:
- Three-dimensional rolling sphere analysis of the site to determine:
- Ground flash density.
- Stroke current range.
- Unprotected area of the site in square feet.
- Expected number of failures due to lightning flashes per year (in the unprotected area of the site).
- Determine proper surge protection devices required for the site ◦Determine voltage and current levels necessary given the lighting flash risk for the site with the proposed lightning protection system.
- Determine where the surge protection devices must be installed on the site.
Lightning Protection System Design
A lightning risk assessment and a lightning protection system is critical to helping ensure managed power quality for facilities and sites. Lightning assessments and protection systems are carried out to help protect employees, visitors, equipment, electrical systems and critical business processes. Electrotek provides comprehensive lightning risk assessments and lightning protection plans which include a full detailed report with findings and recommendations for implementing a lightning protection system that meets NFPA 780-2017 requirements.
Electrotek lightning risk assessments and lightning protection designs include:
- A review of the existing lightning protection system against national standards (NFPA 780-2017 and IEEE 998-2012).
- An assessment of the risk of a lightning strike to people, buildings and equipment at facilities and sites.
- A calculation of risk and a determination of whether a lightning protection system is needed.
- A description of the proposed lightning protection system including:
- A list of the recommended protection system components, surge protection devices and accessories required to provide the necessary level of protection.
- The location of the components, devices and accessories to be installed.