When lightning strikes a structure with inappropriate lightning protection system, it can cause damage to the structure, its occupants and assets. These damages and failures can extend beyond the structure being struck. It can cause hazard, involve local environment, and breakdown of utilities in vicinity. The scale of hazardous consequences depends on the characteristics of structure, structures in vicinity, utilities associated to structure, shielding philosophy employed within the structure, coordination philosophy of protection system, etc. apart from characteristics of lightning flash.

Types of Damages

Apart from loss to human life, lightning causes damage to structure, public utilities and cultural heritage. This involves flashes to the structure, flashes near the structure, flashes to the utilities connected to the structure, flashes near the utilities connected to the structure, flashes created due to induced stresses within the structure, recoverable/unrecoverable damage to the equipment employed in the structure and data loss.

What is a Lightning Protection System?

The lightning protection system (LPS) comprises of air termination, down conduction, earthing, equipotential bonding, surge protection system and fail-safe scheme during lightning condition.

Safety through design

Apart from ensuring protection to people and services connected to the structure, LPS ensures protection against direct and indirect lightning strikes to structure and high value assets vulnerable to failure due to surge caused by lightning originated electromagnetic pulse (LEMP). This can be achieved by proper assessment during design conforming to:

  1. Risk Assessment calculations as per IEC 62305-2
  2. Radius of protection calculations as per NFC 17-102, JUS, I20
  3. Proper selection and sizing of the components of LPS as per IEC 62305-3
  4. Measures and selection of Surge protection devices as per IEC 62305-4
  5. Striking distance for substations as per IEEE 998

Further zonal protection layout needs to follow electro-geometric modelling as per Rolling sphere method, involving angle of protection and mesh conductor, for conventional air terminals and Radius of protection method as per NFC 17-102, for ESE air terminals.

A Lightning Protection System should be

  • Designed as per internationally accepted standards by a qualified engineer
  • Installed by a competent contractor
  • Commissioned i.e. verified and validated after installation by third party inspector
  • Monitored annually by auditors

Installing off-the-shelf products without adequate design does not ensure 100% safety against lightning. Effective and 100% safe lightning protection system not only mandates use of products conforming to specification but also necessitates understanding contextual design variables and implementing customized solution.

Example/Case Study – Bringing the energy of the sky safely down to the heart of the earth

Lightning flash density of Dubai as per BS6651 is two. This means Dubai experiences two lightning flashes per square km per year. As the height increases, the lightning risk also increases. In these circumstances, a 100-meter high building of 30 floors is approximately at 5 times more risk compared to a 50-meter high building of 15 floors.

Burj Khalifa is presently the world’s tallest skyscraper with a height of over 820m and a true engineering marvel. However, this height brings with it new challenges to keep it safe. The tower is designed for multiple purposes including residential, hotel, commercial, office, entertainment, shopping, leisure, and parking facilities. This tower houses external delicate assets like sonometer, obstruction light, cctv, etc. at difficult to access locations. The assets, residents and occupants are at a high risk of hazard and loss due to lightning strike.

Design Challenges

  1. Due to the height of the structure lightning strike can be initiated from below the cloud that are higher than Burj and above the cloud that are lower than Burj. This causes a unique challenge of catering to both polarities of lightning repeatedly.
  2. The Burj Khalifa is a vertical city with the challenge that, when lightning travels from top of structure to the bottom, it can induce an electrical surge in the systems installed along the vertical expanse endangering the safety and security.
  3. Extremely delicate and highly sensitive assets are mounted within 1.5m of the lightning protection system and they must not be damaged by side flash during lightning.
  4. Earthing system is inaccessible and buried, hence deploying permanent earthing system is mandatory. As per Dubai Municipality, seismic zone factor of Dubai is 0.151, which necessitates use of non-crack system in earthing.

Design Solution

The integrated passive and active LPS installed at Burj Khalifa is carefully designed to withstand approximately 100 bipolar lightning strikes during its lifetime (at least 2 strikes/year). Presently, lightning has struck the tower over 20 times on the air terminal without effecting concealed electronics in the vicinity. After the lightning strikes, it travels vertically over 820m through the central core while ensuring safety of life and assets. Over and above, use of earth enhancing compound for soil treatment and a permanent earthing system gives ZERO MAINTENANCE feature to its earthing system.

Repeatedly protecting high value, near vicinity delicate assets from direct strike and conducting it over 820m is a world first achievement.

To know more about Lightning Protection System Design write to us at info@manavenergy.com or call us on +91-9611378007

Have a look at the video below as Richard Hammond, Discovery UK as he joins an engineer and travels right to the top of the spire of the Burj Khalifa:

Reference

  1. Baker, W. F., Korista, D. S., & Novak, L. C. (2007). Burj Dubai: Engineering the world’s tallest building. The structural design of tall and special buildings, 16(4), 361-375. https://doi.org/10.1002/tal.418
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