Can a Thermal Camera be used for Fever Detection?

And can you use these Security Cameras to Re-open your Business?

With COVID-19 spreading across the world, shutting down businesses, a lot of hype is being generated around installing a thermal camera for fever detection.

Thermal cameras for fever detection have been used almost exclusively by airports. However, they are now being installed in warehouses, meat processing plants, cruise ships, conference centers, and factories. Government, healthcare, and education institutions are also increasing their use in areas where people could gather or interact.

The result has caused a huge demand and increase in thermal camera sales. Mobotix has seen a 175% year-on-year increase in April, Thermoteknix’s Q1 sales tripled, and Ogpal has sold more units in the past two months than they had in the previous 7 years.

Is a Thermal Camera the Answer to Fever Detection?

Can this really work to slow the spread of COVID-19?

Our opinion is that a thermal camera should not be installed as your ultimate solution to fight COVID-19. Thermal cameras are not medical devices and they are not built to detect a fever. A thermal camera is built to detect variances in heat. For security purposes, when pointed outside at a field, for example, it can detect a person walking at a far distance.

That being said, there are two situations where it could be worthwhile:

  1. Where Government regulations require employees to undergo thermal screening before being allowed to enter a workplace
  2. Where the perception of implementing systems to prevent the spread of COVID-19 is more important than the end result

If governments impose regulations saying that a business can re-open if they measure the body temperature of employees, then a thermal camera for fever detection could meet that requirement. Installing one camera at a factory entrance could be more cost-effective than the labour cost of having employees take the temperature of everyone who comes in. A camera is also not at risk of contracting the coronavirus. As such, fever detection cameras could be good for your business and for your employees.

Implementing these cameras can impact the perception of your business in the public eye. T&T made national headlines when they started scanning the temperatures of customers entering their stores. T&T has found that employees and customers alike appreciate the temperature checks. Amazon was one of the first to implement thermal cameras to detect fevers.

Thermal Camera Fever Detection T&T

3 Major Concerns with Thermal Cameras for Fever Detection

We have three major concerns when it comes to using a thermal camera for fever detection.

  1. The suitability of thermal cameras to slowing the spread of COVID-19
  2. The ability of thermal cameras to accurately detect fevers, and
  3. The procedures used to implement fever detections cameras into current security systems and company practices

A thermal camera used to detect a fever on a person is tricky. Many manufacturers are marketing their thermal cameras as being able to easily scan a room and give accurate readings of each person. The reality is, if you are installing a thermal camera for fever detection, it needs to be installed in a controlled environment and should only be scanning one person at a time. The camera cannot be near a door, window, or even a heating/cooling vent. Even if a person stands outside for 30 seconds in colder temperatures, the reading can be off by 3-4°C.

Here are some best practice guidelines for installing a thermal camera for fever detection.

How accurate are thermal cameras for fever detection?

The accuracy of Thermal Cameras can be measured by comparing the rate at which temperature reading cameras correctly identify whether a person has a fever.

There are four possible outcomes when a camera measures a person’s skin temperature. The thermal camera will take a reading and determine either that the person’s skin temperature is higher than a set threshold. The camera reading then needs to be compared to an actual reading from a medical thermometer.

Therefore, the four possible outcomes are:

  1. A person is detected to have a fever, and in fact they have a fever – a True Positive
  2. Camera detects a fever, but in fact they do not have a fever – a False Positive
  3. Person is not flagged to have a fever, but in fact they do – a False Negative 
  4. Camera determines the person doesn’t have a fever, and in fact they do not have one – a True Negative 

It would of course be best if the camera produced all True Positives and True Negatives. However, 100% accuracy is nearly impossible even in laboratory settings. For the purpose of detecting people who may have the coronavirus, false positives are better than false negatives.

People who are incorrectly determined to have symptoms can be screened out with further tests, whereas people who have the virus and are not identified are not able to continue to potentially pass the virus to others.

Thermal Cameras for Fever Detection are Guaranteed to Produce False Negatives

No matter how you set them up, thermal cameras are guaranteed to produce false negatives in four common situations:

  1. Anyone who is asymptomatic or pre-symptomatic
  2. Somoene who has taken medication to reduce their fever symptoms
  3. A person whose temperature is being taken while they are in or have recently been in cooler air temperatures
  4. Anyone who engaged in exercise within 10-15 minutes of having their temperature scanned or who was out in the cold

A Thermal Camera cannot detect people who are asymptomatic or pre-symptomatic because these people are not experiencing any symptoms. This means that they do not have a fever. You can’t screen for something that isn’t there.

People who are pre-symptomatic later develop symptoms, but they are still contagious and could pass the virus to others.

Current research estimates that between 25% and 80% of infected people could be “silent spreaders”. These are alarmingly high rates. None of these people would be flagged by a thermal camera.

Likewise, Thermal Cameras would not detect a fever in anyone who had reduced their symptoms by taking Tylenol and Advil.

Additionally, thermal cameras may also produce false negatives if people have recently exercised or were recently in colder weather. This is because they rely on measuring skin temperature rather than internal body temperature.

Skin Temperature is not the Answer

Skin temperature is much more susceptible to changes in ambient air temperature and in normal environments is usually offset by about 3°C. This offset is fairly consistent if the temperature reading is taken between the eyes. The thermal camera software can be calibrated to provide more accurate measurements.

While calibrating the skin offset can compensate, thermal imaging cameras remain vulnerable to fluctuations in ambient air temperature. This means that on hot days, the camera is likely to detect more false positives; and on cold days it is more likely to miss people who actually do have fevers.

Surprisingly, skin temperature drops about 2°C during exercise. And in the face, it takes 10-15 minutes to return to normal. This means that if an employee with a fever was running to avoid being late to work, for example, the thermal camera might record their temperature as normal instead of flagging them for further screening.

So your saying they don’t work?

If you are planning to implement a thermal camera as a medical device to detect an illness, such as a fever, then I wouldn’t recommend it. If a thermal camera is just being used as a precaution and pre-screening tool and the proper installation methods are followed, then it can work.

That being said, what happens when the camera detects a person’s skin in the fever range? Do you set off an alarm? Do you send an email alert?  These are all questions that need to be answered before you rush out and purchase a thermal camera.

If you like this article and want to learn more, you may want to visit our information page on Thermal Cameras for Fever Detection.