Do the buildings you manage have lightning protection?
Lightning protection acts as a safeguard, it’s designed to protect a structure by intercepting extremely high currents of strikes and passing them safely from the structure to the ground, via a network of air terminals, conductors and ground electrodes.
Without lightning protection, you as a property owner or facilities manager may be putting occupants at risk. Not only protecting a building’s structure, contents and surroundings should be of priority, but also the tenants within the building.
What are the Australian Standards for Lightning Protection?
To decide the level of protection required for any building, you must first determine the type of building it is and its contents. In all cases, lightning protection is required to provide protection for personnel within any building. Additional protection may be required if what is located inside the building as classified as ‘sensitive equipment.’
What are the Building Type requirements?
Type I Building is defined as a building with metal cladding on the roof and all walls. Lightning can strike the building and it will flow to ground, via the cladding. The steel framed, reinforced concrete buildings with metal cladding provides almost total protection. The cladding acts as both an air terminal and down-conductor (the cladding must be connected to the earthing system). A building without electronic equipment and basic surge protection e.g. main switchboard surge diverters and telephone protection on MDF is necessary.
Type Ia Building is similar to type I, except it contains electronic equipment and associated equipment: outdoor antenna, sensors, etc. In this case full protection is necessary and the protection boundaries must be established.
Type II Building is constructed from reinforced concrete or steel framed with no metal cladding. All steel frames must be connected together and bonded to the roofing if it’s metal. The steel frames may act as the down-conductors.
Type IIa Building is similar to type II, except it contains electronic equipment and associated equipment: outdoor antenna, sensors, etc. In this case full protection is necessary and the protection boundaries must be established.
Type III Building is constructed from materials substantially free of metal. Down-conductors must be installed externally to the building and earthed to the building earth. A lightning stroke counter should be fitted in at least one down-conductor to measure lightning strike activity. The strike counter should be waterproof with a reset button inaccessible without the use of tools and the unit powered by a long life battery of minimum 10 years.
Type IIIa Building is similar to type II, except it contains electronic equipment and associated equipment: outdoor antenna, sensors, etc. In this case full protection is necessary and the protection boundaries must be established.
For non metallic roofs, apply the rolling sphere analysis method, explained below. The rolling sphere analysis may also be used to design placement of finials of large flat roofs.
(Building Types courteous of Novaris Pty Ltd)
How does a Lightning Protection System protect a building?
The standard Lightning Protection Design endorsed in the AS1768 Standard is based on the Rolling Sphere Methodology. This methodology is said to roll over the whole structure for protection. All areas of the structure that the sphere touches are considered to be exposed to direct lightning strokes, and would need to be protected by the placement of lightning rods, or air terminals.
The diagram below depicts the Rolling Sphere Method (RSM).
In general, air terminals need to be installed in such a way that the rolling sphere only touches the upper surfaces. If the sphere is to touch the outer section of the structure, then additional air terminals should be installed at those points. The values of the rolling sphere radius are based on four protection levels:
|Level 1 Protection||20 Metre Rolling Sphere|
|Level 2 Protection||30 Metre Rolling Sphere|
|Level 3 Protection||45 Metre Rolling Sphere|
|Level 4 Protection||60 Metre Rolling Sphere|
Some structures are more at risk of being struck by lightning. The risk for a structure is the area size, the height and the number of lightning strikes per year per mi² for the area.
Lightning protectors should be placed where they will prevent the sphere from touching a structure. A weak point in most lightning systems is in transporting the captured discharge from the lightning rod to the ground.
Lightning Protection Systems are used to lessen or prevent lightning strikes from damaging structures. These systems lessen the fire hazard which lightning strikes can pose to structures. A Lightning Protection System provides a low-impedance path for the lightning current to lessen the heating effect of current flowing through flammable structural materials. If lightning travels through porous or water-covered materials, then these materials can explode if their water content is turned to steam by heat produced from the high current. This is an example of why trees can be often shattered by lightning strikes.
What are the main components of a Lightning Protection System?
The parts of a Lightning Protection System consist of:
- Air terminals (lightning rods or strike termination devices)
- Bonding conductors
- Ground terminals (ground or earthing rods, plates, or mesh)
Air terminals are placed at or along the upper points of a roofing structure and are electrically bonded together with bonding conductors (down conductors or down leads). These are connected by a direct route to one or more grounding (earthing) terminals. The connections to the earth electrodes must not only have low resistance, but must have low self-inductance.
How does a Lightning Protection System work?
A Lightning Protection System provides a conductive path between an air terminal and earth, so that when a building is struck by lightning, the majority of the lightning’s current follows the path of the Lightning Protection System, with substantially less current traveling through flammable materials.
Damage to a building occurs when high voltages travel too quickly and bypass surge protection equipment. Because lightning can send extremely high voltages into an electrical installation, arcs can jump at multiple places, which can cause mechanical damage and ignition to a building.
Lightning can enter a building in four ways:
- Striking a metal object on the roof, e.g. antenna, cupola, air conditioning unit extending upwards, or alike
- Striking a building directly
- Striking a tree or silo near the building and travelling to it
- Striking a power line or wire fence, then travelling into the building
Can Lightning Protection be installed after a building is constructed?
Installation of a Lightning Protection System should ideally be done during construction as the AS1768 Lightning Protection Standard specifies that the conventional design should be designed and installed during construction, as this type of Lightning Protection System can be difficult to retrofit to existing buildings, and would require down conductors to be installed vertically on the external walls every 20 metres. These conductors also require to be clipped every metre or so, as the system can be visually unsightly and detract from the aesthetics of the building.
During construction, structural rebar within the concrete may be used to carry lightning current to ground where there is a continuity of the rebar from roof to ground. Where this continuity is not assured, the use of dedicated down conductors is recommended.
These systems are very labour and component intensive, where the install costs can be considerable as an overall percentage of the systems cost.
Alternatively, there is another Lightning Protection System which is commonly used, the non-conventional design, although it is outside of the scope of the AS1768 Lightning Protection Standard.
Is lightning protection a legal requirement?
The Australian Standard AS/NZS 1768-2007 ‘Lightning Protection’ provides useful guidance in this respect, and it is recommended that whilst this is not a “mandatory” standard, if the recommendations and design considerations are implemented in their entirety, the greatest level of acceptable protection can be afforded to both equipment and personnel.
The AS/NZS 1768:2007 Lightning Protection Standards Australia provides guidelines for the protection of persons and property from the hazards of lightning. It applies to conventional Lightning Protection Systems consisting of air terminations, down-conductors, earthing systems and surge protective devices. It also provides a comprehensive risk management process for the determination of the risk of damage due to lightning for a range of structures.
This Standard sets out guidelines for the protection of persons and property from hazards arising from exposure to lightning. The recommendations specifically cover the following applications:
- The protection of persons, both outdoors, where they may be at risk from the direct effects of a lightning strike, and indoors, where they may be at risk indirectly as a consequence of lightning currents being conducted into the building.
- The protection of a variety of buildings or structures, including those with explosive or highly-flammable contents, and mines.
- The protection of sensitive electronic equipment (e.g. facsimile machines, modems, computers) from over-voltages resulting from a lightning strike to the building or its associated services.
The nature of lightning and the principles of lightning protection are discussed and guidance is given to assist in a determination of whether protective measures should be taken.
What standards must be met with Lightning Protection Maintenance?
Lightning Protection Systems are sophisticated networks. Not only does weather, such as extreme temperatures and high winds affect lighting protection equipment, but also building upgrades involving new construction, building additions, re-roofing or remodelling and changes to electrical, mechanical or communication systems can also affect a system’s performance.
Because changes are likely if not inevitable, all electrical building maintenance schedules should include annual lighting protection equipment maintenance.
A Lightning Protection Test and Earth Grid Test must be carried out when the installation has been completed and should be done by a licensed electrician. By law, certified testing must occur within a two-year time frame. To ensure thorough and correct maintenance, a Lightning Protection Test checklist should be followed.
- A properly designed Lightning Protection System safeguards vulnerable structures, equipment, and trees by providing an easy path to a ground, which harmlessly dispels the electrical charges. Protection should also be provided for objects located where a lightning strike’s current might side-flash, such as electrical wires or metal devices on building roofs.
Installation of a Lightning Protection System must be designed and installed by a professional. Codes and standards must be followed.
Scheduling maintenance of your lightning protection, surge protection and earthing solutions is paramount. With routine maintenance, we will:
- Inspect lightning rods and other equipment for damage
- Check for loose connections
- Monitor new roof installations and equipment
- Confirm that down-conductors have a continuous path from ground electrode system to lightning rods
- Inspect lightning surge protector devices
- Report on system for compliance with current codes
For more information, or to book a lightning protection test or electrical maintenance inspection, call Prolux Electrical Contractors today on 1800 800 880.