As more organizations bring thermal imagers into the workplace and public spaces for skin temperature screening, the advantage of this solution has become clear: pre-screening people for signs of an elevated skin temperature can be an effective component of procedures aimed at reducing the spread of infection. With the right camera system and software, thermal imaging can be very fast and provide accurate, actionable measurement results.
FLIR EST™ thermal imaging cameras and software solutions offer specialized measurement modes and alarms that can easily identify when an individual is exhibiting high skin temperatures—a possible sign of fever, which, in turn, is a potential symptom of COVID-19 infection. These solutions initiate an alarm when the measured temperature exceeds a set threshold. While it might seem appropriate to set a fixed absolute threshold of 37.2°C (99°F), there are several factors that can affect skin temperature. FLIR EST solutions offer an intelligent screening mode that takes these factors into account.
Unlike a medical thermometer you use at home, a thermal camera cannot measure a person’s core body temperature. These cameras are only capable of detecting surface temperatures, so they are best used to measure the area at the corner of the eye (inner canthus) where the skin is thin enough to provide a reading close to body temperature. Even so, temperatures measured at the inner canthus are usually a few degrees lower than body temperature— somewhere between 33.5°C and 36.9°C (92.3°F and 98.4°F).
Skin temperatures tend to vary throughout the day, fluctuating with changes in the environment or even time of day. The same person will likely have a different skin temperature in the early morning compared to an afternoon on a sunny day; their temperature can change due to high activity or simply because they’ve spent time in a cold, air conditioned environment. In fact, research has shown that an increase of 10°C (18°F) in ambient temperature can lead to a skin temperature increase of up to 3°C (5.4°F).
These skin temperature fluctuations make screening for elevated temperatures more challenging. Determining whether someone may have a fever therefore cannot be related to an absolute temperature. The temperatures of people with and without fevers should be seen as a continuum that will inevitably overlap. This is important to consider when setting alarms for elevated skin temperature screening.
Defining an absolute temperature threshold for alarm may result in two unwanted effects:
- False alarms: Setting the threshold too low may have the camera detect elevated temperatures with people who do not have fever.
- Missed fevers: Setting the threshold too high is at the risk of missing people who have a fever but remain below the threshold temperature.
Aggregating these temperature fluctuations into one absolute temperature that works in all environments does not make sense. Even when measurements are made inside in ambient room temperatures, there are too many variables to account for all skin temperatures. People who have just stepped inside from a hot afternoon will generate different skin temperatures than people who spent the whole day in an air-conditioned store. The system might not alert on a person chilled by AC and then alarm on everyone coming in from the outside heat.
To have an efficient detection system that captures fever cases in varying ambient conditions, we need to have a threshold that adapts. The goal is to determine a relative temperature, i.e. compare the elevated temperature of one person to a succession of other people from the same environment.
This is exactly what FLIR Screen-EST™ on-camera screening mode and computer software can do. The systems are designed to collect temperature samples and compare a new temperature measurement to the sampled average. FLIR Screen-EST on-camera mode is available on a wide range of FLIR thermal imaging cameras, including a new line of T5xx-EST and Exx-EST models. FLIR also offers Screen-EST computer software that runs the averaging process automatically.
Regardless of whether it is on-camera or on-computer, Screen-EST records temperatures from several human subjects to determine an average relative temperature. The system then can be set to alarm when the average is exceeded by a specific amount—say, 1°C (1.8°F). This average must be updated periodically by adding new samples throughout the screening operation. This can reduce the impact of changing skin temperature from person to person and environment to environment, maximizing elevated skin temperature screening accuracy.
Screening and medical evaluation
FLIR EST thermal imaging cameras and software solutions make it possible to organize screenings in high-traffic areas such as airports and hospitals more efficiently. However, a thermal imaging camera cannot provide a medical evaluation. If the camera detects an individual with elevated skin temperature, that person should then be evaluated by a medical professional through a diagnostic interview, a medical thermometer, or through a combination of both.