An easy-to-use, online lightning risk calculator that considers these factors and produces a risk report for a specific structure is available without cost at www.bit.ly/LightningRisk. While this tool can be used with new construction or existing buildings, it is most advantageous to conduct the lightning risk assessment early in the design process.
There are applications for which an LPS should be considered regardless of the outcome of the risk assessment. These include factors such as:
- the presence of large crowds, where continuity of critical services is required (e.g. hospitals and power generating stations);
- facilities containing explosive or flammable materials; and
- sites of irreplaceable cultural heritage.
Additionally, LPS is required for most military and nuclear construction, and many AHJs (e.g. Alberta Infrastructure and SaskPower) frequently require lightning risk assessments.
CSA B72:20 cautions:
“Lightning can result in indirect losses that sometimes accompany the destruction or damage to buildings and their contents. An interruption to business… can involve losses quite distinct from and additional to the losses arising from the direct destruction of material property. There are cases where whole communities depend on the integrity of a single structure for their safety and comfort… A stroke of lightning to the unprotected chimney of a pumping plant, for example, can result in a serious shortage of sanitary drinking water, irrigation water, or water for fire protection.” (§C.7)
If lightning protection is required
“The function of a lightning protection system is to provide a means by which a lightning discharge can enter or leave the earth while eliminating or minimizing damage to the structure on which the system is installed,” as succinctly stated by CSA B72:20 (§0.1).
An LPS does this by providing a low-impedance path to safely conduct lightning through a building, between earth and the atmosphere. The path includes:
- strike termination devices (such as air terminals, also known as lightning rods) and conductors on the roof and other elevated locations;
- grounding electrodes;
- a conductor system connecting the roof-level and ground-level systems by means of down conductors;
- interconnecting conductors to provide equipotential bonding connections throughout metallic building elements and systems; and
- surge protective devices on power, communication, and data lines penetrating the building envelope.
A fuller discussion about LPS elements and system design is in the authors’ previous paper, “Lightning Protection: Five Concepts you Need to Understand,” in the March 2016 issue of Construction Canada. The Lightning Safety Alliance, in conjunction with lightning protection professionals across the nation, also provides continuing education classes.
Most of the revisions to CSA B72:20 will not be noticeable in the field except by experts. However, the following changes will be apparent to most construction industry professionals walking a jobsite.
Prior to the update, intercepting conductors could be installed on parapets and roof ridges without the benefit of air terminals. As a result, lightning strikes were apt to perforate parapet caps and roofing materials. Air terminals are now required in those locations.
Air terminals must now project a minimum of 254 mm (10 in.) above what they protect; an increase from the previous requirement of 50 mm (2 in.).
Rooftop equipment was previously permitted to be simply bonded to the main lightning conductor. Now, rooftop units must be provided with air terminals and conductors if they are not in a zone of protection offered by lightning protection installed on higher elements of the structure.
Standard electrical conductor (e.g. No.2, #2/0) was previously permitted to be used in an LPS. In the new edition, only conductors and components labeled specifically for lightning protection may be used.
The recommendation against sharp bends in conductors did not define any limits. Now, bends must have a 200 mm (9 in.) minimum radius.
Copper components are no longer permitted in contact with steel or galvanized steel. Instead, aluminum is required in these locations to prevent galvanic corrosion.
Another important distinction is that CSA B72:20, “does not cover installation requirements for early streamer emissions systems or charge dissipateon/charge transfer systems. No recognized standards body or testing agency exists for Canadian installation of these devices.” (§1.3)
