why do we require protection against lightning
Cloud to ground strikes are the most dangerous form of lightning for property and more importantly human life. Lightning Protection Systems increase the safety of properties, structures and surrounding areas by offering the energy from a lightning strike an easy path to ground, where it is safely dispersed. Each year in the USA lightning is recorded as the cause of injury or death for hundreds of people. While over 10% are killed by lightning, 70% are seriously injured. Those that survive are often left with lifelong severe medical problems. Lightning strikes from thunderstorms on average cause more deaths in the USA than hurricanes and tornadoes combined. It is estimated that every year, lightning is responsible for millions of pounds (sterling) of damage in the UK alone and nearly m billion dollars (US) worth of damage worldwide. This figure is believed to be growing as IT systems and communication networks become more important to business and their usage expands. The immense current caused by a lightning strike generates a large amount of heat, less heat is generated when this current travels along a conductive material with low electrical resistance. Air is not a good conductor compared to other materials like copper so as the massive lightning currents travel through it, it becomes super heated to temperatures 3. 5 times hotter than the surface of the sun. This burst of enormous heat produces an intense flash of light and causes a shock wave of thundering sound. If lightning does this to air, imagine what it can do to the unprotected structure of your property. The electrical charge in lightning is always seeking the path of least resistance to ground. If lightning strikes a property the intense charge will search for the easiest route to ground no matter what it is; metal plumbing, pipes, radiators and taps, the wiring of a communications network and telephone system, metal railings on a stair well or the wiring carrying the mains electric that is not designed to carry such enormous loads.
Anything touching or connecting to these objects is also highly likely to be injured or damaged. If the material carrying the current has too high an internal resistance the huge passing current, even though brief, will generate large amounts of heat causing primary damage by melting, igniting the conducting material or violently exploding it by rapidly expanding any air or moisture contained within. Secondary damage may also be caused by any resulting fire within the property, devastating contents within the building directly or from smoke damage. With a lightning protection system properly installed the potentially dangerous current from a lightning strike is offered an easy and safe route to ground. Workplaces in the Britain have a duty to ensure the health, safety and welfare of their staff under the Health and Safety at Work Act 1974 Section 2(1). Events must be thoroughly risk assessed, and if there is a risk of being struck by lightning this must be investigated and control measures like a lightning safety plan put in place. This may include the installation of building or regional lightning protection systems to create lightning protected areas. The UK requires structural lightning protection to comply with BS6651:1999. This standard focuses on the protection of the building structure only from lightning strikes something which is also required by most insurance companies. Is Lightning Protection Still As Important Today As It Used To Be? It is even more important today than it used to be. Todays competitive businesses are demanding more sophisticated electrical systems and communication infrastructures.
A lightning strike to an unprotected building today can cause greater destruction even if it is not visually apparent like structural damage or fire. Even an indirect lightning strike on a building or nearby utility can cause thousands of pounds of damage as its currents radiate out from the strike zone. With the global climate also changing, it is predicted that Britain will experience more thunderstorms and lightning strikes in the future.
The principle consists in creating one or more preferred impact points for a lightning strike using low impedance, conductor elements. These then conduct and dissipate the lightning current into the ground. This coherent system enables the lightning to be captured and dissipated whilst providing protection to the structure. There are five types of lightning protection systems for protecting structures against lightning: Rods, Meshed conductors, Catenary wires, Early streamer emission lightning protection system, Protection by natural components, Benjamin Franklin invented the Lightning Rod in 1753. This lightning conductor is made up of a 2 to 8 m high tapered metal rod that dominates the structure to be protected and which is connected to minimum two down conductors and two earthing system. As the protection radius of this type of Air-Termination Rod is limited to around 30 meters environ (Lightning Protection Level = IV, height = 60 meters), it is normally only used to protect small structures or zones such as pylons, chimneys, tanks, water towers, aerial masts, etc. This lightning protection, derived from the Faraday cage, consists of meshed conductors that cover the roof and walls of the structure to be protected. Air terminals are positioned around the edge of the roof and on high points.
A network of conductors follows the external perimeter of the roof. This network is completed with transverse elements. The mesh size is between 5 and 20 meters according to the effectiveness required. The top of the down conductors fitted to the walls are connected to the roof mesh, and the bottom to dedicated earthing systems. The distance between two down conductors is between 10 and 20 meters according to lightning protection level required. The largest part of lightning current is conducted and dissipated through the conductors and earthing systems closest to the point of impact of the lightning strike. This lightning protection system, using a similar principle to that of the mesh cage, consists of a mesh of conductors, but at a distance from the structure to be protected. The aim is to avoid the lightning current coming directly into contact with the structure. and dedicated earthing systems. The size of the mesh and the distance between down conductors are subjected to the same rules as for the meshed conductors lightning protection system. This protection requires that additional mechanical studies (resistance of materials for masts, qualifying ground pressure, resistance to wind and weather condition, etc. ) be carried out and insulation distances defined. The catenary wire lightning conductor is particularly used to protect open areas when there is no architectural support or hazardous storage. Components that have a lightning protection function but that were not installed for this purpose. Comment: these are conducting parts of a structure or building that are able to participate in the external protection through their capacity to capture a lightning strike or to conduct lightning current.
They can be used to replace all or part of a down conductor or in addition to an external installation. Sheet metal covering the volume to be protected, provided there is no risk of them being perforated by an impact Metal components of a roof structure (interconnected steel frames, etc. ), even if covered with non-metallic materials, provided that these may be excluded from the volume to be protected Metal rods in reinforced concrete, provided that there is electrical interconnection between them, and particularly with the capture means and earthing system Metal parts such as gutters, decoration, guardrails, etc, provided that their cross-section is not less than that specified for normal components Metal pipes and tanks, provided they are at least 2. 5 mm thick and if perforated, do not cause a dangerous or unacceptable situation These elements must comply with thickness, cross-section and continuity requirements, thus making their use a difficult matter. The principle of an early streamer emission lightning conductor is to artificially generate, with the aid of an ionization device, an early upward leader occurring before the other natural upward leaders, in order to establish a privileged impact point of the lightning strike. Diagram showing the operating principle for capturing a lightning strike using an early streamer emission conductor Because the capture of a lightning strike is quicker than with a lightning rod, this technology can be used to protect zones spread over a wider area, thus ensuring the protection of large structures. The protection radius generated depends on the lightning conductor's triggering advance value (Dt in ls), its height and the effectiveness of the protection, the maximum value being 120 metres (Level III, height = 60 metres).
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