New Delhi: The image of a temperature gun pointed to a person’s head has become synonymous with the Covid-19 pandemic. Thermal scanners, popularly known as temperature guns, have been at the forefront of mass surveillance during this pandemic.
They are being used to screen for fever at almost all public places — from malls, markets, offices, restaurants, grocery stores, hotels, to airports and metro stations.
Doctors who have been at the frontline of the pandemic, however, are questioning the accuracy of the thermal scanners in recording temperatures accurately.
Their effectiveness is also under question considering that at least 80 per cent of coronavirus patients in India are asymptomatic.
How do thermal scanners work?
Thermal scanners are designed with an infrared sensor that can measure the surface temperature without coming in contact with the person.
In order to get a surface reading, these cameras ‘calibrate against a black body’. A black body is referred to as a surface that can absorb all radiations striking it. Typically, it is a small hole in a box with an interior which is blackened.
The camera gauges the difference between the temperature of the subject and the black body’s predetermined temperature. While the thermal scanner can be used to detect fever, which is one of the symptoms of coronavirus, it can’t be used to detect the infection itself.
Dhruv Aggarwal, spokesperson of Dr Odin, an India-based online store for healthcare products, explained the working. “Infrared thermometer is a kind of thermometer that uses the principle of radiation to measure human body temperature,” Aggarwal said in an email. “Its infrared sensor only absorbs the infrared radiation of the human body and does not emit any radiation to the outside world.”
The email added that the infrared thermal radiation of the human body is focused on the detector. The detector converts the radiation power into an electrical signal, which can be displayed in the unit of temperature after being compensated for the ambient temperature.
Simzo Electronic Technology, a China-based manufacturer of thermal scanners being widely used in India, also explained the technology behind its thermal screener. Kevin Li, sales manager, wrote in an email, “Any object can generate a certain proportion of infrared radiant energy as per its own temperature…This thermometer is designed to detect infrared radiation at 5 to 14 um wavelength by highly precise infrared sensor.”
Can’t ‘swear by’ thermal scanners
There is, however, a glaring lack of scientific evidence on the effectiveness of the thermal scanner in detecting Covid-19.
In February 2020, a study attempted to probe the effectiveness of airport screening through thermal scanners and estimated that 46 per cent of infected travellers wouldn’t be detected.
Doctors say that even though oral thermometers couldn’t possibly be used for mass-screening during the coronavirus pandemic, they couldn’t ‘swear by’ thermal scanners either.
Dr Rommel Tickoo, associate director, internal medicine at Max Hospital, Delhi, told ThePrint, “Thermal scanners are meant for screening, they aren’t foolproof. Just because you don’t have temperature at that particular moment, doesn’t mean you’re Covid free.”
“One can’t swear by it, the thermal scanner can miss out a lot of cases,” he added.
Dr S. Chatterjee, senior consultant, internal medicine, Apollo Hospital, Delhi, said figures being recorded by the thermal scanner weren’t reflecting the ‘true’ temperature of the body.
“I think thermal scanners are a total failure, it doesn’t record temperature properly,” he said. “I would blame whatever is happening in India with regard to the coronavirus situation to thermal scanners because their screening isn’t effective at all.”
Unable to distinguish between skin & body temperature
The thermal scanners are designed to detect elevated skin temperatures but aren’t precise enough to distinguish between the warmth of a person’s skin and their core body heat.
Even when this reporter was screened using a temperature gun and it recorded a higher temperature, she was asked to wash her face with cold water. After which, the temperature detected was much lower so she was allowed to enter the premises.
This instance emphasises the difference between skin temperature and body temperature, one which thermal scanners are unable to account for.
Speaking on the issue, Dr Tickoo explained, “In light of this, checking oral temperature is more accurate. With digital machinery, there is always a difference of 1°F.”
When asked about whether coming out of a hot car, or walking up the stairs could affect the warmth of the skin, Dr Chatterjee said, “Yes, that does cause a difference in temperature reading. But even considering the difference between skin temperature and body temperature, I haven’t seen the thermal scanner recording temperature correctly anyway.”
The companies, however, defended their products.
“Our thermometer is specially researched to measure the temperature through the forehead and ear. And the accuracy for forehead and ear is ± 0.2 °C in laboratory conditions,” Dhruv Aggarwal, Dr Odin’s spokesperson, explained.
Kevin Li, sales manager, Simzo, explained via email, “At laboratory conditions, during measuring temperature of 34.0℃ to 42.0℃, Simzo’s measuring accuracy is ± 0.2℃. Further, during measuring temperature of 42.1℃ to 43.0℃, the measuring accuracy is ± 0.3℃.”
It must be noted that a difference of either ± 0.2℃ or ± 0.3℃ could determine whether an individual needs to isolate or not.
Standardisation & regulation
ThePrint found that the thermal scanner was recording different readings for the same person at the same time. This raises concerns regarding standardisation.
When asked about how these devices are standardised, Dr Odin’s spokesperson responded, “Generally, it’s normal that several thermometers give different readings because the point is your measure every time is not exactly the same and hence the temperature will be marginally different.”
Simzo’s Kevin Li said they measured black bodies as standards. “Black body must be sent to Chinese Metrology Institute for inspection and testing. After it is passed, certificates are issued to them,” he wrote.
ThePrint contacted Dr V.G. Somani, Drugs Controller General of India, to get a comment on how the quality of this device is regulated. Dr Somani remained unavailable for a comment.
A source from the Health Ministry who didn’t wish to be named revealed that the thermal scanner has not been recognised by the department as a medical device for quality control or regulation.