Thermal imaging cameras: How to detect fever against Coronavirus COVID 19

Thermal imaging cameras to detect temperature

The architecture and engineering sector is widely recognized use of infrared thermography in different technical situations with professionals amply trained.

infrared thermography has been with us since 1958 approximately, for uses of the construction , civil and industrial, experimenting in the last 15 or 20 years a great growth. The thermal cameras are more intuitive, ergonomic and offer increasingly better images providing more accurate analysis.

We were curious to recognize how can use thermal cameras in the face of the current pandemic caused by the coronavirus COVID-19 given the scarce information – in Spanish – that is on the net.

An example with a thermal camera to measure the temperature in action we find it in the following video…

Here, we have met Sergio Melgosa Revillas who is a expert and trainer in infrared thermography with your company EBuilding that has told us and clarified many concepts, doubts and procedures of how the thermal imaging camera can detect fever in people . So we started…

Relation of COVID 19 and thermography infrared

The company Flir Systems , has been working and perfecting fever detection systems with thermography ( Fever screening ) from 1999, with the first Asian epidemics (We assume that there are other companies, but in security chambers temperature , at the level of Spain, is well known).

In 2003 the first permanent posts of fever detection in airports in Asia, and today, Flir Systems guarantees an accuracy of 0.5 degrees on models of cameras suitable for Screening such as the ranges Exx , T-Series and A320 .

This means that there is enough experience and bibliography to build confidence in this method of fever detection , which, as we will see, provides many advantages.

By infrared thermography we will be able to find people with a higher body temperature higher than the average of the people reviewed, which which may be indicative of having a fever, and, in which case, those people would go on to a second review more in depth.

The generalized symptoms of the Coronavirus in broad strokes would be those indicated in the following image that we can also find more information and answer questions from the WHO here:

The usual methods for measuring the temperature in people who are using generalized form are three:

• The first, the thermometer contact.
• The second, an infrared thermometer which is usually placed in the ear (some also allow it on the forehead).
• The third method, thermography infrared .

The infrared thermography means you don't have to touch the patient and also keep the operators away from the direct contact with the people being checked (Yes we will need a workplace with a stable temperature where you can control the flow of people who are going to review).

We remember that we wrote an article about a mobile with thermal camera or how modern security cameras too they use infrared at night.

Like every diagnostic technique and equipment, we find ourselves with some limiting factors that we must be aware of, especially in this context…

Limitations in the use of thermography infrared

• By definition, body temperature is the internal body temperature . This temperature we will NOT be able to measure it with a camera thermal since these equipments do not cross the human tissues. We can only measure temperature surface , logically at a lower temperature than the internal.
• In addition, due to some technical aspects of the infrared radiation and thermographic cameras, neither we can measure the absolute temperature of the surface, if Well we don't have to.
• The technique we will use will be based on detecting a thermal abnormality in one person , out of a group of people with a specific average temperature. Must therefore assume that the majority of people who we will check are healthy people and that the person presenting a higher temperature (1ºC for example) is the one that You will probably have a fever.
• We must also consider that there is a lot of thermal variability between people, according to their metabolism, age or sex , so we may not detect all cases of possible fever of the analysis group.

Fever and thermography infrared

As we know, human beings are isothermal (We all remember what they taught us in school: hot-blooded and cold-blooded beings, terms already disused), and this forces us to maintain an optimal temperature operation, regardless of the environmental conditions that surround us:

• If our central core gets too hot, exceeding 37 ºC, the refrigeration would begin by evaporation (sweating).
• If the temperature drops below a certain level, they start bodily processes to generate heat (shivering, for example).

We define normothermic temperature as the temperature of a healthy person, and this varies between 36ºC and 37.8 ºC. To make it a little clearer, in the following image details:

The rise in temperature is the body's response before any disease or infection and is a typical indicator doctor, along with blood pressure and pulse. So… How is it possible to measure temperature at a distance and without direct contact with the object we measure?

The fever manifests among other things, with a elevated temperature in the head . This facilitates the use of infrared thermography since as we have said, we will not go through fabrics or materials (clothes). Although, the most precise areas before a temperature chamber , are the cavities that we find in the head; the ear and the eyes.

The thermal cameras do not measure temperature, they detect radiation intensities . It is related to the temperature already enters into the physical laws that are studied and necessary to work in the field of thermography (For those interested in learning more, there are quality courses that can be consulted from HERE in Ebuilding)

In addition, there are factors that affect the amount of radiation that leaves the body (emissivity), the one that reflects the body (reflectivity) and even to the possible attenuation of the atmosphere that stands between the object and the camera. By luckily, all these factors are practically irrelevant when we work with people, being the human body an excellent emitter of infrared radiation , and, in In general, we can use values for default .

Methodology for the detection of Fever with thermal cameras

Let's remember that we are looking for people with a temperature higher than the rest , for the same situation. So the first thing to determine is what is means normal temperature.

We will assume that people will have a similar temperature, under the same conditions (ambient temperature, movement, etc.), as long as they do not have a fever. And we will also assume that most people do not have a fever. So, whoever have a significantly different temperature from the rest, She probably has a fever.

How can we determine an average temperature for measured with thermal cameras? Can we select the first 20 people to establish the mean of temperature of a healthy person, and, based on this, establish the line from which we will establish the fever:

• The average temperature line will serve us for the rest of the days, although we can check our temperature mean with other newly chosen samples.
• In the case of SARS, the WHO recommended detecting the minus 1ºC above normal temperature . This can serve as an example in the case of COVID-19 if not there is another indication in this regard by some authority sanitary. Below 1ºC we can run the risk of have numerous false positives.
• Both the average temperature and the line that marks the fever should be recorded and reviewed at intervals newspapers. If we observe that we have numerous false positives (positives in the thermal camera that are later discarded by health personnel), we must adjust the limit fever to 1.1 or 1.2 ºC instead of 1ºC.

Yes we establish an average temperature of the healthy person 36.0ºC (remember that we are talking about the eye socket), a detected temperature of 37.0 ºC or higher would already be a case of possible fever and should go to the assessment of health personnel for a second review with ear thermometer and already under the protocols of the staff sanitary.

The people in charge of detecting fever with thermography will be in the first line of fire in the fight against the disease, and therefore their exposure to risk will be the highest (They must know the protocols of personal protection – PPE used).

Now, we have to locate the best possible site for the fever screening post . This place has to have:

• A reasonably stable temperature and be spacious. Queues will probably form to pass in front of the thermal camera.
• If several thermal camera stations are to be set up, must assess, since a single position in a very tumultuous (e.g. airport) can be counterproductive and generate nervousness in the population.
• In space or proximity, personnel will be needed security, to avoid misconduct or negative examination, and medical personnel to care for people with fever following the corresponding protocols.

Today There are advanced software that allow you to configure alarms and detect fever in areas with higher crowd of people . This should be appreciated and opt for the best possible solution that allows more revisions fast without compromising high reliability.

Regarding the personnel in charge of the fever screening , we have:

• Camera operator : will be responsible for the placement of the camera and its adjustments (focus, parameters etc). And who decides if that person passes the control or requires review by medical personnel. His concentration must be maximum since the task is very repetitive and long lasting.
• Helper : will control the flow of people before passing in front of the camera, making sure that they do not wear glasses, caps or any other element that prevent the correct capture of the image.
• Support person : will direct the people marked as positive (fever) towards staff for evaluation, thus preventing the operator and the assistant interrupt his work and the queue of people slow down In addition, you can answer people's questions, take notes of interest, etc.

Obviously, “scanning” with a camera to measure temperature can only detect infected people who are already showing symptoms of fever. The scan of temperature to detect possible cases can let pass people who incubate the disease, but it can certainly be a "first screen" that can help streamline a more extensive detection of the pandemic.

We remind you that we wrote an extensive article on types mask; hygienic, surgical and PPE (FFP1, FFP2 and FFP3, and what are its characteristics and when should we use them.