The value of accuracy

As public premises begin to reopen there is an increasing need to find solutions to ensure the safety of those entering these spaces. With a plethora of approaches and methods to evaluate, choosing a solution that is proven and accurate is vital to effective business recovery.

Applying a holistic, accurate approach to COVID-19 risk mitigation is key to reducing the costs of business disruption. Shutting down facilities for deep cleaning and the loss in confidence by customers, staff and other stakeholders has a dramatic impact on business as does the growing risk of business liability.

The Importance of Temperature Accuracy

The need for accuracy of data to help protect your customers, staff and business is clear but how do you gauge the effectiveness of different solution types, the differences in technologies and cost points? Accuracy, specificity and relevance are key considerations needed when deploying sensors for the detection of febrile temperatures.

Temperature screening is an important tool to help ensure community and business safety while building the required confidence to assist in the post pandemic recovery.  Elevated temperature/fever (87.9% of reported cases) along with shortness of breath, fatigue and other flu like symptoms are indictors of COVID-19 and other infections.

While temperature screening alone will not diagnose or solve the COVID-19 crisis, it is a proactive approach that will help minimise risks and protect against further waves of the virus.

Studies show that checking other vital signs such as heart and respiratory rate in addition to temperature increases identifying infected individuals by almost 50%.

Cost vs safety

Built for home or built for health?

Lower cost thermal sensors tend to use thermopile and pyroelectric technologies that do not offer high resolution outputs. These sensors are well suited for their primary intended functions  in home appliances or intrusion and movement detection.

With the increase in demand for temperature screening some providers are using these sensors to provide low cost solutions that are not fit for purpose, particularly for unmanned deployments.

Specificity Detects Areas of Elevated Temperature

Thermopile and pyroelectric technologies often claim accuracy of     -/+0.5 degrees Celsius, however because of the low resolution they do not have the specificity to correctly detect areas of elevated temperature and do not comply with the ISO IEC 80601-2-59 standard for thermographic febrile skin detection. Thermography is the technique for detecting and measuring variations in the heat emitted by various regions of the body and transforming them into visible signals that can be recorded photographically.

Why Resolution Matters

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Elenium Sensor Array
(100k temperature pixels) XVGA
Thermopile Array
(2.2k temperature pixels) 48×47 pixels
Higher resolution sensors detect more temperature points on a person’s face. They can also determine temperature in a 2-3mm² area of interest (such as a human tear duct) from 0.5 meters. Low cost sensors technically rated for -/+ 0.5-degree accuracy will not have the capability to return values specific enough to a location on a person’s face that is exhibiting febrile skin. This will result in higher false negative rate.

On target

A person’s external skin temperature can be on average up to 1.5 degrees Celsius cooler than their core body temperature. Targeting areas like the tear ducts, where blood vessels flow close to the skin’s surface helps to provide a reliable reading. In unmanned, self-service deployments if the resolution of the sensor is low, point of region targeting is not possible.

More To Accuracy Than Meets The Eye

Taking a temperature reading from the correct location on a person’s face is critical to ensuring a reliable reading.

Simply targeting the center of a user’s forehead or taking an average temperature across their face will lead to false negative results. Accurate and reliable solutions must be able to detect which region of interest on a user’s face it will use to take the temperature reading. Regions of interest are different from user to user.

Regions of interest are locations like a user’s tear duct, or where supraorbital blood vessels are closest to the surface of the user’s external skin.

Cost vs safety targeting 

Did you know?

Contactless medical thermometers typically use sensors that are as low as 16 temperature pixels (4×4 pixels). Because they are human operated it is up to the administrator to target a valid area on a person’s face to take a reliable temperature reading. If the administrator does not target the correct area the reading will reflect the temperature of the target area and miss the elevated febrile skin.  This is the case for manual temperature screenings not conducted by trained medical professionals.

What is Accuracy?

The FDA guidelines require the offset error (often described as accuracy) to be -/+ 0.5 degrees Celsius. To determine the uncertainty rate additional factors like sensor drift, and stability need to be considered.

ISO IEC 80601-2-59 formula for calculating accuracy in a laboratory setting:    

Accuracy formula

How to evaluate health screening options

When evaluating different temperature screening solutions that claim to have an uncertainty rate of -/+ 0.5 ask the vendor the following question:

  1. What is the drift rating for the sensor? – it should be less than 0.1 degrees Celsius tested over a minimum of 14 days.
  2. What is the stability of the sensor?  – it should be less than 0.1 degrees Celsius
  3. Does the temperature pixel uniformity measure 0.2 degrees Celsius or better?
  4. Does the solution take into consideration background temperature as part of its emissivity correction function?
  5. Does the solution have enough resolution to target reliable areas of interest?
  6. How does the solution consider ambient or transfer temperature fluctuation?
  7. Is the accuracy claim for a lab or a real-world environment?
  8. Does the solution comply with the ‘Essential Performance Requirement’ of the ISO IEC 80601-2-59 standard ?

Other Factors Impacting Accuracy and Reliability

Ambient Environment 

The greatest factors impacting relative accuracy and reliability of temperature readings are ambient temperature and humidity.

Changes in ambient temperature during operations can dramatically affect the reading of a sensor. This impacts lower and higher cost sensors. The overall solution needs to compen sate for this through thermal management, emissivity correction calculations and real time calibration using thermal reference sources.

The Elenium Sensor Array creates a protective thermal barrier between the thermal sensor and the ambient environment to mitigate the effect of sudden transfer temperature changes.

Emissivity Calculations 

Emissivity is the ratio of energy radiation specific to a material. In the case of human skin the ratio is 0.97. Most low-cost solutions simply divide the emissivity ratio from the sensor reading to correct for emissivity. However, this simplified approach does not take into consideration factors such as, ambient temperature, moisture or curvature of skin.

Why does this matter?

If a solution is sensitive to sudden environmental changes it will fail in locations where the temperature can suddenly change such as doorways or near heating and cooling vents. A solution may also be affected as more people fill a space and their body heat increases the room temperature. In an airport terminal or a shopping mall the impact can be up to 4 degrees Celsius.

Fit for recovery

The world will recover from COVID-19 and many of our practices will change. Beyond this pandemic increased attention to hygiene and health screening will continue. Understanding the science of accuracy means you can confidently make technology  choices to protect the wellbeing of all your stakeholders. Elenium Vitals offers a solution with tested accuracy that can swiftly evaluate key vital signs on a one-to-one basis while overcoming environmental impacts such as sunlight and air temperature. The value is in a tested, efficient solution that allows staff to focus on their job while reassuring all entering the premises that their wellbeing is taken seriously and protected.

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