SAFETIS EV: Fire Safety Thermal Imaging Sensor
19. 12. 2023
SAFETIS EV: FIRE SAFETY REVOLUTION
12. 2. 2024- Temperature screening should always take place indoors. If it is not possible to execute measurements indoors, an environment approaching indoor conditions should be chosen.
- Accurate measurements require an air temperature between 18° C and 24° C, with a relative air humidity of 10% to 75%. Since moving air cools the face, both wind and air conditioning should be kept to a minimum.
- It is absolutely necessary to eliminate the direct incidence of sunlight, which warms the skin and disrupts temperature measurement.
- The person being screened must look at the camera lens, and they cannot wear glasses, which are opaque for LWIR thermal cameras.
- To achieve accurate readings, operators must select correct measurement parameters, the most important of which are emissivity and reflected apparent temperature. See the relevant entry below for more information on these settings.
- The spatial resolution on the face of the person being screened should be at least 1 mm per pixel. This requirement circumscribes the distance between the thermal camera lens and the person being screened. For a thermal camera with a standard resolution of 320x240 px, the ideal distance ranges from about 25 to 30 cm, depending on the angle of view. Warning: some manufacturers advertise an accurate measurement distance of several tens of metres, but this is technically impossible without a significantly higher camera resolution.
- We recommend a higher thermal camera resolution of 640x480 px, which enables the fulfillment of the IEC 80601-2-59 technical standard [2] at a distance of at least 1 metre between the thermal camera and the inspected person - depending, once again, upon the angle of view.
- A black body provides constant metrological traceability, through which the thermal camera is continuously recalibrated. This recalibration is repeated at least every 5 seconds. To ensure measurement accuracy, the black body must have high temperature stability, low indicated temperature uncertainty, and occupy an area of at least 20x20 px in the image of the thermal camera. This circumscribes the distance between the thermal camera and the black body.
- The highest-accuracy region within the thermal image (thermogram) is the area nearest to the black body. Therefore, the face of the inspected person should be located so that the scanned surface of the face in the image is as close as possible to the black body, which is usually placed behind the inspected person's shoulder.
- Temperature must be measured in the area medially adjacent to the inner corner of the inspected person's eye, as indicated in Fig. 1. This is due to the stability of the temperature in this area, as it is directly above one of the "branches" of the carotid artery. This area is one of a few regions on the surface of the human body that reaches a temperature close to the body's core temperature.
- It should be emphasized that operators cannot be interested in the minimum, nor the average, nor even the highest temperature reading. The only reading that matters is the temperature measurement in the area medially adjacent to the inner corner of the inspected person's eye. Facial temperature cannot be represented by one value "above the rectangle", as illustrated by Fig. 2.
- Other screening procedures almost always lead to lower temperature measurements.
