Lightning Rods–Sharp Tip or Blunt for Safety?
The flashing, searing bolt of lightning is a direct threat to life and buildings. Passing through a conductive channel from the cloud on its way to the ground, lightning’s electrical charge develops heat, close to 28,000° Celsius. Trees and buildings can ignite from direct hits, causing disastrous fires. Atop a building or other structure, a properly installed lightning rod diverts the danger, but achieving safety measures required experimentation over centuries.
Lightning strikes CN Tower in Toronto frequently, about 75 times annually. The heavy duty lightning safety equipment prevents disaster. Photo: Duncan Rawlinson (CC BY-NC 2.0)
Reducing property damage with lightning rods
“Trust in Providence and Repair the Powerhouse,” was the prevailing wisdom regarding lightning strikes over a century ago. The introduction of properly installed lightning rods made it “possible to reduce the chances of loss to a minimum,” said Prof. W.C. Blackburn in “Inspection of Lightning Rod Installations,” Ontario Agricultural Review (OAC), March 1920.
Without an overseeing authority for rods, the early customer was required to learn about installation and perform the inspection themselves. “Unless this is done, the seeker for protection is simply courting destruction,” said Blackburn, “for a badly rodded barn or dwelling is more unsafe than one which lacks a rodding system.”
Benjamin Franklin preferred pointed tips
Before atmospheric science was understood, American inventor Benjamin Franklin aimed to prove that pointed rods would attract lightning. His first step was to ascertain that lightning and electricity were similar phenomena. Making a kite with a 30-cm-long piece of pointed wire as conductor, Franklin tied a silk ribbon with a key to the kite’s string. From the key, he ran a wire attaching a Leyden jar—a type of capacitor. A storm at Philadelphia in October 1752 was just what Franklin needed, and he sent the kite into the sky, hoping for a lightning hit.
Lightning indeed struck. When Franklin “moved his hand near the key he received a shock because the negative charge attracted the positive charge in his body,” stated Benjamin Franklin Historical Society. In Franklin’s opinion, the test proved that “the tips of rods should be pointed instead of rounded to that they could draw electrical fire out of a cloud silently.”
Franklin’s conclusion that a sharply pointed rod was the proper equipment held for many years, but there was dissent. England’s King George III disagreed with the scientist, and instead installed blunt-tipped lightning rods in his palace. Centuries later, King George was deemed correct, said John Noble Wilford in “Lightning Rods: Franklin had it wrong,” New York Times, June 14, 1983.
But blunter tips were safer, according to report
Wilford quoted a Journal of the Franklin Institute report from New Mexico physicist Dr. Charles Moore noting “‘that the electric fields above the blunter rods were as much as two times stronger over greater distances than those above the sharp rods’’” The blunted rods more effectively directed the lightning toward the earth than the sharp rods, arguing against Franklin’s discovery.
From his evaluations, Moore determined that “’conventional, sharply pointed lightning rods fail to protect structures beneath them from lightning, and that they often do not provide the preferential path to ground for lightning currents in the vicinity.’” Pointed lightning rods appear to protect themselves, creating “around their tips a dense sheath of electrified, or ionized, particles, which reduce the probability of lightning’s striking the rod.” The lightning finds nearby targets instead, causing hazardous conditions. The physicist suggested that a two-centimetre tip or wider for the rod tip was preferred.
The Government of Ontario enacted the Lightning Rod Safety Act in 1922 and instituted strict conditions and bonds.
Enacting C 297 in 1922
In 1922, the Government of Ontario enacted C 297 Lightning Rod Act to establish “some control over the installation of lightning protection systems and reduce the lightning-related losses of insurance companies,” said John M. Tobias in “The Basis of Conventional Lightning Protection Systems,” IEEE Transactions on Industry Applications,” July/August 2004.
The Act prescribed annual licencing of a person or company for the sales of lightning rod equipment and installation. The licencing fee was $50, payable to the Treasurer of Ontario, according to the Lightning Rod Act of 1927; the permit was received only on approval of the Fire Marshal upon meeting strict conditions, plus a hefty bond of $5,000.
Approved agents required to have licence
Once licenced, the firm could add “a suitable person to act as his agent in this Province” who could provide certified proof “of his good reputation and character signed by the mayor or reeve” of his municipality. If the candidate met the Fire Marshal’s approval, the agent was issued a licence “upon receipt of a fee of $3.”
Improving lightning rod standards
Standards for lightning protection improved since the launch of the 1922 Lightning Road Act. “New considerations include advanced surge suppression technology, more quantifiable methods of risk assessment, and new models for the lightning protection zone,” wrote Tobias. Studies in the early 2000s suggested that “blunt air terminals with a certain radius of curvature seem to have an advantage over sharpened air terminals in receptors of lightning strike.” However, opinions and test results continue to vary, and research is ongoing.
On January 1, 2011, the Lightning Rod Act was repealed, ending the Ontario Fire Marshal’s responsibility.
This article first appeared in January 2025 in Ontario Construction News. (C) Susanna McLeod