As the locks are released, thermal cameras are popping up in all kinds of public places to assess people’s health.
What do thermal imaging cameras do?
Using infrared technology, thermal imaging cameras detect radiant heat from a body – usually the forehead – and then estimate the body’s core temperature. These cameras are an extremely powerful tool, often deployed by firefighters to track hot embers and police to search for suspects out of sight.
But they are not intended to be medical devices. How useful are they in the current pandemic?
They can give a reasonable measure of skin temperature, to the nearest half a degree – but it’s not the same as body temperature.
“These devices, in general, are less accurate than thermometers for medical devices like the ones you stick in the ear,” said Derek Hill, professor of medical imaging science at University College London.
What is normal body temperature?
About 37C (98.6F). A high temperature is generally considered to be 38 ° C or more. But the normal temperature can vary from person to person and change throughout the day. It can also fluctuate during a woman’s monthly cycle.
Taking an accurate measurement of central body temperature is not easy. Although it can be measured on the forehead, mouth, ear and armpits, the most accurate way is to do a rectal reading.
37 ° C(98.6 ° F) normal body temperature
38 ° C(100.4 ° F) or higher, high temperature / fever
Do thermal cameras detect coronaviruses?
No, they only measure temperature. High temperature or fever is just a common symptom of the virus. Others include nausea, headache, fatigue, and loss of taste or odor. But not everyone with the virus has a high temperature and not everyone with a high temperature is infected with the coronavirus.
Thus, thermal imaging cameras alone will miss infected people with other symptoms or no symptoms at all – known as false negatives. They will also identify people with fever for another reason – known as false positives.
So are thermal imaging cameras useful?
Temperature control alone “may not be very effective,” says the World Health Organization. The cameras must be correctly configured and take into account the ambient temperature. One risk is that the cameras could put operators to sleep in a false sense of security.
“They’re … just one of many tools,” said James Ferryman, professor of computer vision at the University of Reading.
What if I wear a face mask or a tarp?
“The heat that radiates from the skin is likely to be affected by wearing face masks,” says Professor Ferryman.
This is why most temperature measurements are based on the forehead, which is usually exposed.
Will I be warmer if I exercise?
Not necessarily. The temperature of the skin actually decreases during exercise because perspiration appears on the surface of the skin.
The body is good enough to regulate its temperature even after exercise, so it should be really high enough to appear.
How else do I take my temperature?
With portable thermometers pointed at the forehead. They do not need to touch the skin, but should be a few inches from it. Although accurate to a fraction of a degree near skin temperature, they correctly detect fever about 90% of the time compared to a rectal thermometer, says Professor Hill.
Where can I expect to be temperature tested?
Thermal scanners are now in place at some UK airports – including Bournemouth. The temperature control is being tested for some passengers at Heathrow, while Manchester Airport says the equipment is also being tested – but the results will not be communicated to passengers or “used to influence whether a customer can travel”. The international ferry port of Portsmouth has also installed a thermal scanner to filter departing passengers.
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Schools are deploying portable laser thermometers to check children every morning. And some employers are planning to introduce staff testing in the workplace.
At work, do I have to take a temperature test?
Under UK employment law, individuals must agree before an employer can monitor the temperature of staff members. Certain employment contracts will already allow this type of test to be carried out, by what is called “implied consent”.
If employees don’t agree – and there is no pre-agreed policy covering the situation – then taking the temperature of someone is illegal, says the professional organization for HR and people development. Employers must also treat medical information they collect fairly and transparently – according to the Information Commissioner.