3 Select the right optics. Check the
field of view (FOV) and measurement
field of view (MFOV), which defines the
smallest spot size that can be measured
accurately. 4Set the emissivity for temperature
measurement on human tissue to 0.98. 5 Set the temperature span for
maximum contrast on face
temperatures (typically from 23°C to
40°C) and apply colour isotherms to
highlight the hottest temperature on the
human face, which makes it easier to see
a person with temperatures outside a
normal range. 6The span and isotherm settings
depend on ambient temperature
variations, so optimal setting is important.
For differential thermography methods,
measure tear duct temperatures of test
subjects and set alarms for 1-2°C above
that average temperature, ensuring
you adjust those settings if the ambient
temperature changes. 7 Camera software should be set
to alarm visually or audibly when a
temperature inside the area tool exceeds
a set threshold. This can be combined
with camera snapshots. You should set
your own alarm threshold based on the
degree of sensitivity to false negatives
and positives (and based on advice from
medical professionals).
MANUFACTURING/FACILITIES – FEVER SCREENING
8Eyewear and sunglasses are opaque in
the 8-14 μm infrared spectrum. They
should therefore be removed before the
individual screening. Contact lenses do
not need to be removed as these do not
cover the tear duct.
INFLUENCES OF EXTERNAL
SKIN TEMPERATURE
It is important to recognise that
temperatures taken on the outside of
the body – even at the tear duct – will not
match the core body temperatures taken
using a traditional oral thermometer. In
addition, during fever screening, a number
of factors can influence the external
temperature of the skin.
Medications, including aspirin,
acetaminophen/paracetamol and
ibuprofen or other antipyretics, will reduce
the human core and also skin temperature
and make it impossible to detect a fever
condition, while the evaporative cooling
effect from perspiration will decrease
outside skin temperatures, particularly
when a person is positioned below air flow
vents. Those who are visibly perspiring will
not deliver temperature measurements
useful for fever screening with an IR
camera or any remote infrared device.
Vascular dilation can also occur
after alcohol consumption, increasing
skin temperatures, while high blood
pressure, pregnancy and other physical
conditions can also result in increased skin
temperature. Furthermore, influences
from extremes in ambient temperature,
such as a long walk through a cold car
park, will impact measurements, possibly
masking a fever and reporting a false
negative reading.
LIMITATIONS
Most IR camera technology systems were
designed for versatile fields of application
and can be effectively used in EBT
(elevated body temperature) screening
applications. However, it is vital to know
the limitations of the technology.
None of the IR cameras available on
the market are able to reliably detect and
recognise Coronavirus. Only a registered
doctor can determine whether a person
with elevated body temperature is ill
or infected. Thermal imaging cameras
may generate a distorted perception of
safety, as an unremarkable temperature
measurement suggests a person is not
infected with the virus; even if that person
is in fact infected (a false negative).
However, IR cameras can provide
a reliable indication of elevated body
temperature and the possibility of illness.
Therefore, this technology is a great
support tool during this crisis in order to
interrupt infection chains in advance.
Autumn 2020 www.operationsengineer.org.uk 41
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