Thermal imaging - it is about saving lives !
At our airports in the world, thermal imaging technology is being used on a daily basis to detect the body temperature of people, in an attempt to identify fever and viral infections.
The main concern to raise and question to ask is whether this technology is being used correctly and how important is it for the people using it to be properly trained to interpret the results adequately?
With the recent Corona virus outbreak, letting one subject slip through the system with an apparently normal, healthy temperature could have catastrophic consequences.
Individual 1: Healthy. Max temperature rating: 35,7°C. Distance: <20 cm from individual; image taken at a perpendicular angle. Individual 2: Diagnosed with flu and a fever. Max temperature rating: 36,4°C. Distance:<20 cm taken at an angle.
How does the technology work?
All objects on earth emit infrared radiation. We measure infrared energy radiated from an object by electromagnetic waves. Thermal imagers “see” temperature by measuring emitted radiation and converting this data to a corresponding image.
The greater the radiation being emitted by an object the higher the temperature and conversely, less emission results in lower temperatures.
Most thermal cameras operate in the 8 to 14 µm range of the electromagnetic spectrum.
With the thermal imaging camera acting as the receiver, it displays a temperature picture, providing us with an informative thermal pattern that the human eye isn’t able to detect.
Today, where technology plays a leading part in our everyday lives, thermography is becoming one of the most accepted forms of analysis in a number of unique situations: Where we need to achieve visible results, unseen by the human eye; when it is dangerous or uncomfortable to touch certain objects or where touching them might infect or contaminate the subject.
Thermal imaging cameras and handheld or non-contact thermometers are only able to measure surface temperatures and the thermometers only measure the average temperature of the object being inspected.
What are the important factors to take into account?
How active the person has been just prior to the scan, the time of day, how far the subject is from the instrument, large temperature variations outside of the body and taking scans in an uncontrolled environment are just a few of the many factors which need to be taken into account and which can result in inaccurate readings.
The operator plays a significant role. If the image is not properly focused the temperature reading will be affected. Interpreting and understanding the theory behind the technology is of utmost importance. This will enable the operator to not only be able to read the temperature but also to interpret the thermal patterns to understand what represents a red alert.
It is of the utmost importance that the subject stands as close as possible to the thermal imaging camera or digital handheld thermometer when the scan is being carried out. Close scans ensure true measurements.
The further away the subject stands from the target the more likely it is that external factors will influence the readings.
Accurate temperatures are taken in the area closest to the tear duct.
Max temperature rating: 34,3°C; distance: 1,5 m from individual. 2. Max temperature rating: 34,7°C; distance: 1 m from individual. 3. Max temperature rating: 35,1°C; distance: 50 cm from individual. 4. Max temperature rating: 35,7°C; distance: <20 cm from individual.
These external factors include the ambient temperature, humidity, air-conditioning, wind speed and movement, all of which play a significant role in the optimised results.
Air-conditioning and/or moving air will result in convective cooling – cooling the actual temperature of the subject. Sweat can also have the same effect. As the sweat evaporates, it helps cool your body. The resulting thermal pattern will display a cool colour, such as blue, giving the operator the false impression that there is no significant or alert temperature.
1. Thermal pattern indicates evaporative cooling at the cooler colours caused by sweat.
2. Little to no evaporative cooling – clothes serve as insulation.
Body temperature may actually be 0,6°C or more above or below 37 °C and might change throughout the day, depending on how active you are and the time of day. Body temperature is very sensitive.
As thermal cameras and thermometers cannot scan through glass, spectacles should be removed.
1. Thermal image with glasses in focus: distance: 50 cm; max temperature rating: 35°C. 2. Thermal image with glasses out of focus: distance: 50 cm; max temperature rating: 34,8°.
Preparing the camera for a scan
The correct settings should be entered into the camera: The operator should compensate for the ambient temperatures by the use of a mini vane anemometer. The emissivity value of the object of concern must also be adjusted in the device (human skin 0,98).
The correct level and span should be used and the image should be taken in the manual range setting using a narrow span. A temperature alarm on the thermal camera can be set, alerting the operator to a potential problem. Hand- held thermal cameras can be placed on a tripod to ensure stability when images are taken.
If you pick up a problem – what is the next step?
These can include taking a close up thermal image in a controlled environment at a distance, between the camera lens and object of interest, of no further than 20 cm. It is advisable to take a thermal image of the individual’s tear duct where neither clothing or sweat can affect it, enabling as accurate a measurement as possible with the instrument being used.
Thermal image in focus: distance: 50 cm; max temperature rating: 35,9°C. 2. Thermal image out of focus: distance: 50 cm; max temperature rating: 34,5°C.
Minimum requirements of the thermal imaging device
If you are scanning for a viral infection, it is important to have an instrument which is sensitive enough to detect very small temperature variations and an operator who is properly trained to understand the limitations of the technology and how to interpret what they see.
There are also minimum specifications that the device should adhere to, to ensure optimum results.
The detector type should be a focal plane array, uncooled microbolomoter 320 x 240 pixels. This will givens that you will have 76,800 temperature measurements per image. That is the power of 76,800 handheld thermometers in one.
Because of the body temperature variations, the thermal Imaging camera should be sensitive enough to detect small temperature variations.
The thermal sensitivity of the unit should have at least a NETD of ≤ 0,07 °C, 70 mK .(Millikelvin).
Thermal Imaging Cameras is only an aid to assist, it can be very useful, when operated and interpreted correctly, in picking up problems which can then be investigated further.
Written by: Jeanri Mellanby
Level III ASNT Thermographer and trainer with more than 13 years experience as a Thermographer in various applications.