SINGAPORE — A photo of a lightning seemingly striking the side of a housing block in Queenstown went viral on social media last weekend (April 23).
The photo, taken by a Facebook user named Mak Wei Seng, showed a lightning bolt striking the side of Block 53, a 43-storey block of Housing and Development Board (HDB) flats on Strathmore Avenue.
The online community was abuzz with people asking why the lightning bolt did not strike the lightning rods at the top of the building. Others expressed concerns about the safety of the building and residents living in it.
TODAY spoke to three experts for some answers to the burning questions people wanted to know, with one expert saying that it may be time to re-examine Singapore’s building designs in relation to lightning protection.
WHAT DID THE AUTHORITIES SAY ABOUT THE LIGHTNING STRIKE?
In a statement to TODAY, the Building and Construction Authority (BCA) said that it has asked the building owner to “ascertain if there were any damages to the building and also to conduct an inspection and test of the lightning protection system as a precautionary safety measure”.
Tanjong Pagar Town Council, which oversees the Queenstown public housing estate and manages the common areas, told TODAY that it did not receive any feedback from residents regarding the lightning strike.
“We have checked and there is no issue with the lightning protection system,” the council added.
WHAT PROTECTION DO BUILDINGS HAVE AGAINST LIGHTNING?
Lightning rods are part of a building’s lightning protection system.
Lightning rods are connected to a conductive wire that runs down a building until it reaches the ground.
Lightning protection systems work by providing a low-resistance path for electricity to travel to the earth where it can dissipate safely.
Without protection, buildings hit by lightning can catch fire, cause electrocution or even break off pieces of concrete chunks that can hit passers-by.
Before it issues a temporary occupation permit to a property development, BCA said that it requires a professional electrical engineer to certify that the building’s lightning protection system has been designed, installed and tested to meet the requirements under the Singapore Code of Practice for Lightning Protection, SS555.
Professor Lock Kai Sang from the Singapore Institute of Technology’s engineering cluster said that for tall buildings in Singapore — defined as 45m and above — developers are required to install lightning protection not only on the roof but also at the sides of the building.
He noted that the HDB block in the photo is more than 100m tall.
“Judging from the lightning photo, the building level struck by lightning was well above 45m – probably around 90m,” he said.
“For a tall building, the upper part of the down-conductors and the horizontal bonding rings of the building also function as a part of the air termination system (equivalent to the lightning rods) to intercept lightning that strikes the sides of the buildings.”
Metallic window frames in a building that could be struck by lightning are bonded to the building rebars of the wall and the floor to form an “equipotential zone”, Prof Lock said.
Rebars are steel bars or wire meshes that cross over each other, which are placed in concrete to make it stronger.
As for the equipotential zone, he explained: “All metallic parts that a resident touch or stand on (in the building) are connected or bonded together to have the same voltage potential. There will be no electric shock hazard when there is no voltage difference between parts of a human body.”
In the case of a low building, lightning will not hit the side of the building, so it is immaterial whether metallic window frames are bonded to the building’s structural steel, he added.
He also said that people in a building are generally safe if they remain indoors during a period of lightning activity, though he acknowledged that if lightning strikes a window frame when a person touches it, “there will be obvious risk”.
However, a lightning protection expert said that people should stay away from metallic window frames, especially opened window frames during a thunderstorm.
This was the caution from Emeritus Professor Liew Ah Choy from the National University of Singapore’s department of electrical and computer engineering. He is also chairman of the technical committee for the Singapore Code of Practice for Lightning Protection, SS555:2018.
IS IT NORMAL FOR LIGHTNING TO STRIKE THE SIDE OF A BUILDING?
Analysing the photo, Emeritus Prof Liew said that there was “nothing very unusual” about lightning striking the side of the housing block.
The majority of lightning bolts will strike the top of buildings, but a small percentage of lightnings will approach at an angle and hit the sides of tall buildings, he added.
He noted that this was the case for the lightning bolt in the photo.
“The lightning stroke terminated on the side of the tall building instead of on the roof where lightning-protection intercepting terminals are located.
“Not all lightning leaders approach angles from the charged cloud are vertical. Some indeed descend at an angle as in this case here,” he said.
There are factors determining how effective a lightning rod is.
Dr Teo Tee Hui, a senior lecturer for electrical engineering at Singapore University of Technology and Design (SUTD), said that lightning is a kind of electrical energy, which flows though the nearest and lowest resistance path.
“The effectiveness of the lightning rod depends on its position, direction, material, neighbouring buildings, as well as the nature of the lightning bolt.
“Thus, it is possible that the lightning bolt bypassed the lightning rod and hit other parts of the building. In most cases, a lightning protection system must be in place. A lightning rod is only part of the protection system,” he added.
CAN BUILDINGS BE MADE SAFER AGAINST LIGHTNING STRIKES?
One expert interviewed did say that lightning may become stronger and more frequent due to climate change.
For Dr Teo from SUTD, what happened at the HDB block in Queenstown “raises concerns” that it may be time to “revise and enhance” Singapore’s building designs.
As warmer and longer summers heat up the land surface and carbon emissions continue to rise, stronger updrafts are more likely to produce more powerful and frequent lightning.
A 2014 study in the United States estimated that there was a 12 per cent increase in the frequency of lightning strikes with every 1°C increase in temperature.
Therefore, “coexisting building design with environment is getting more important,” Dr Teo added.
In Singapore’s case, he said that it may be necessary to increase the number of lightning rods and coverage across the island.
However, increasing the coverage of lightning rods may not be a simple matter. Dr Teo acknowledged that it has cost implications on the construction industry.
Nonetheless, accounting for a higher risk of lightning may become increasingly paramount.
Dr Teo suggested running simulations testing critical situations to determine what upgrades are necessary.
“As a city-state, the entire country surface is metal. Structures like MRT tracks and stations and high-rise buildings have metal. This provides even lower resistance (making it easier) for lightning to strike,” he said.
CLARIFICATION: In an earlier version of this article, it was reported that anyone touching a window during a lightning strike would be safe and that metal window frames are lightning-protected. Professor Lock Kai Sang has since clarified that not all such window frames are protected, depending on risk factors and building height. More information has been added to elaborate on safety measures regarding windows.