How to get the best readings from thermometers

Distance, hair and sweat can all affect the reading of the temperature scans you've been experiencing at work, shopping malls and schools.

Dr Richard Lessells, an infectious diseases specialist leading the University of KwaZulu-Natal's Research Innovation and Sequencing Platform (Krisp), said non-contact forehead infrared thermometers may provide a measure of reassurance but urged caution around their use during the pandemic. 

“They are unlikely to be an effective part of our response for Covid-19. They are just to reassure people that measures are being taken in most cases. As a public healthcare measure, it’s probably not reliable," said Lessells.

Gordon Smith, owner of AWR Smith Process Instrumentation, which specialises in various portable testing and measurement tools, said it was important to use a thermometer correctly. He offered this advice to get the best results from temperature screening:

• To get the correct temperature, one must make sure the thermometer is at a distance of 5-10cm from the forehead. Too far away from the skin will either display “Lo” or give an incorrect reading.
• The skin must be wiped to remove any sweat.
• No hair, scarves or any obstruction on the measurement areas.
• Avoid testing immediately when a person has excessive clothing or was exposed to air conditioners, cold rooms, wind, sunshine or any other source of radiant heat. Wait five minutes for skin to stabilise
• It is generally recommended that the thermometer be tested and calibrated at least once a year to ensure that it functions accurately.
• Do not put the thermometer where the temperature is too high or too low, damp or direct sunlight, dusty or corrosive gas.

Lessells said one's body temperature can change depending on one's activity.

“Measuring at a single time when entering a place is not an effective way to measure if you have Covid-19. It can be affected by the outdoor temperature and there is confusion on how far [away] one should stand,” he said.

He said as per Covid-19 guidelines, 38°C was the temperature indicating that action needed to be taken.  

However, sometimes outside temperatures affect the accuracy of non-contact thermometers.

“No shame to security guards [screening with non-contact thermometers], but they are not healthcare professionals or [getting] training on how to do the temperature screening properly. This brings a lack of accuracy and reliability,” he said.

Bilal Paruk, who specialises in heating, ventilation and air conditioners, said it was important to buy thermometers from reliable brands.

“In order for a thermometer to work properly, you must regularly get it checked. This process is called calibration. This way it still gives you the correct temperature. It should be done every month or so, but there aren’t a lot of places that offer this service,” he said.

On the accuracy of non-contact thermometers, Paruk said: “The distance they are shooting it from counts. In terms of accuracy, it’s not 100%. People don’t know if their infrared lasers are working properly most of the time. The cheaper ones could be inaccurate.

“Thermal emitting cameras used at the airport are more accurate ... The problem is we can’t trust these thermometers 100%.”

According to Lessells, screening should be conducted through a questionnaire about people's health.

“When people report their symptoms, the information is much better. You want people to report if they have noticed any fever and measured the temperature at home. In terms of supermarkets, you rely on people staying home. But we have to trust people and continue to inform them,” he said.

“It should be effective, but it relies on people being honest and reporting those symptoms accurately. There are a lot of reasons they don’t report - because they fear doing tests and being forced into isolation. Nothing is 100% reliable.”