COVID-19
infection control in existing building design
The recent
spread of the pandemic chinavirus or coronavirus (COVID-19) has brought several new questions
to the forefront with respect to the design and operation of the buildings in
which we spend much of our time, specifically when it comes to infection
control.
Many of us
are asking “how clean are our buildings, really?” and, “what can be done to
control the spread of viruses in a high-density space?” Topics like surface
cleaning and air purification practices that were once the sole domain of the
health care industry are now top of mind in discussions about workplaces,
restaurants, education facilities, retail spaces and grocery stores. With this
renewed interest comes a new market for many high-quality sanitation and air
filtration products — but separating the valid claims from the noise can be
difficult.
HEPA filtration
High-Efficiency Particulate Air (HEPA) filters are most effective at removing small particles.
A standard air high-efficiency particulate air filter
looks and acts much like any air filter in that it captures but does not kill
contaminants. The HEPA designation means that the filter assembly was designed
and tested to capture 99.7% of particles in the air passing through it that are
0.3 microns in size. The 0.3-micron size represents the most difficult particle
size to capture so the 99.7% capture rate actually represents the worstcase
efficiency of the filter. For particles that are larger or smaller than 0.3
microns, the capture rate increases.
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Figure 1: High efficiency particulate air filters can be very
effective in capturing and removing viruses from air streams, as long as they
pass through the filter. Courtesy: Lance Schmittling/Henderson Engineers
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Since most viruses are less than 0.3 microns, HEPA
filters can be very effective in capturing and removing viruses from air
streams. HEPA filters are typically installed in the ductwork and therefore
must rely on the room airflow patterns to carry contaminants to the filter,
small particles like viruses circulate in the room for an extended time before
eventually making their way to the filter for capture. While highly effective
and reliable, an in-duct HEPA filter is more appropriate
in preventing cross contamination between spaces.
Disadvantages:
• Only captures particles from the ducted air — not
within the space.
• Some increase in energy usage due to increase air
pressure drop and motor work.
• Increased maintenance due to filter replacement.
Advantages:
• Proven technology, no moving parts, easily retrofitted.
• Effective at particle entrapment.
• Effective at protecting space-to-space contamination.
Bipolar ionization
Bipolar ionization generators create positively and
negatively charged oxygen ions which bind to contaminants in the indoor air,
either causing them to drop out of circulation in the room or to be captured by
a mechanical filter within an air handling unit. When properly installed,
operated and maintained, bipolar ionization systems can reduce dust and mold,
capture odors, reduce volatile organic compounds and reduce viruses and
bacteria in the air.
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Figure 2: Bipolar ionization generators create positively and
negatively charged oxygen ions, which bind to contaminants in the indoor air.
Courtesy: Lance Schmittling/Henderson Engineers
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Ions generated by these devices typically have a relatively
short life span, so it’s important to regularly pass room air over the ion
generator to ensure sufficient contact. Typically, bipolar ionization
generators are installed in the ductwork or directly in the air handling unit,
but recirculating room units are available through some manufacturers
Disadvantages:
• Emitter wear and calibration requirements.
• Only captures particles from the ducted air — not
within the space.
•
Potential to create ozone byproduct.
Advantages
• Little additional pressure drop added to system.
• Requires no re-engineering of existing HVAC system.
Humidification
Pathogens and infectious droplets travel further in dry
air, especially when the relative humidity is below 40%, which is partly why we
tend to see more illness in the drier winter months. By maintaining indoor
relative humidity between 40% to 60%, building operators can reduce the risk of
spreading airborne infectious diseases in their facilities.
Disadvantages
• Does not capture or kill pathogens.
• Consumes water for humidification.
• Can add significant cost to the system installation.
Advantages:
• Creates a less hospitable building climate for viruses.
• Reduces static.
• Increases occupant comfort in winter.
Ultraviolet sterilization
Anyone who has ever gotten a sunburn is familiar with UV
light’s ability to degrade organic materials. Given the proper contact time and
intensity, UV light can inactivate viruses and bacteria — rendering them
harmless. UV lights can be installed in an air handling unit or even directly in
the space itself, but the light must directly contact the pathogen in order to
be effective. There is no travel distance or “conditioning” of the air that
takes place.
UV light, with a wavelength between 200 to 280 nanometers
has proven to be the most effective for infection control while inflicting
minimal damage to human skin or other mammals present in the space.
Disadvantage
• Does not filter contaminants from the space.
Advantages:
• Can destroy microorganisms like mold, bacteria and
germs.
• Applicable in a room-based or air handlerbased setting.
Body temperature detection
One way to control the risk of infection in your facility
is by detecting potentially contagious patrons before (or as) they walk through
your doors. To do this, one widely discussed solution is the application of
thermal imaging to detect body temperatures. These systems work by using
infrared radiation to evaluate temperature differences on the surfaces of the
skin or other materials. A variety of devices exist with this technology
including ceiling/wall-mounted cameras, handheld thermal imagers or devices
integrated into existing security or building automation systems. Standard can
help to know details procedure.
In particular, the world's two top international
standards groups, the IEC and ISO, have published 3 standards
covering fever (i.e., febrile) screening:
- IEC 80601-2-59:2017 Medical electrical equipment — Part 2-59: Particular requirements for the basic safety and essential performance of screening thermographs for human febrile temperature screening
- ISO/TR 13154:2017 Medical electrical equipment — Deployment, implementation and operational guidelines for identifying febrile humans using a screening thermograph
- ISO 80601-2-56:2017 Medical electrical equipment — Part 2-56: Particular requirements for basic safety and essential performance of clinical thermometers for body temperature measurement
FDA Endorsed
Both
organizations have published detailed standard guides for fever detecting
thermal camera solutions, and the FDA has endorsed them, including in their most
recent guidance stating:
cameras
are tested and labeled consistent with the following standard: IEC
80601-2-59:2017
the
camera's labeling references and is consistent with the guidelines in ISO/TR
13154: 2017
FDA
considers body temp screening cams (paired with a thermometer to confirm the
fever) to be medical devices, technically a "Telethermographic system
intended for adjunctive diagnostic screening". These require FDA
510(k) clearance before being marketed, a process that takes around 130
days. On Apr 17, 2020 The US FDA has declared it will not go after the many companies
marketing unapproved fever detection cameras during the coronavirus public
health emergency, even though it does consider these products medical devices,
it has announced 10 page new guidance ( Click to get enforcement
policy). The FDA says that a 'prominent notice' should
be included, explaining: The labeling includes a prominent notice that the
measurement should not be solely or primarily relied upon to diagnose or
exclude a diagnosis of COVID-19, or any other disease.
ISO give
importance of the inner eye area is best real-life thermal cam images from
the ISO/TR 13154:2017. thermal cam readings must use a blackbody.
The IEC
also states to the OPERATOR to ensure that the FACE is unobstructed by
hair, eyeglasses, and other objects because their presence will interfere with
the ability of a SCREENING THERMOGRAPH to detect a febrile condition. Notably,
ISO states a face mask is also an obstruction, and leads to warmer-than-usual
readings due to warm breath exhalations being reflected back onto the face.
IEC states
the minimum laboratory accuracy for a thermal camera including the measurement
uncertainty shall be less than or equal to an offset error of ±0,5°Cover the
range of at least 34°C to 39°C
IEC states face should be parallel to the camera shall
accommodate a FACE that is positioned 0.75 m to 2.2 m above the floor. This
requirement may be met by moving the infrared camera. The plane of the
lens of the infrared camera also should be parallel to the FACE and in
line with the TARGET.
IEC states cameras must be parallel in order to maximize
the number of pixels in the face image, which should be a minimum 240 by 180.
Many of the manufacturers IPVM are using 400x400
(e.g., Sunell's Panda Cam) or smaller 320x288 sensors, which means they
could only comply with this when reading a single face, not 10 or more in a row
or the 40+ shown in marketing details.
The
ISO/IEC standards make no mention of such AI or of anything else helping
overcome these obstructions. This sets up an issue where manufacturers may
argue these 2017 standards are out of date.
Some
manufacturers have also touted "compensation algorithms" they claim
automatically adjust for the (well-known) difference between face skin
temperature and actual body temperature. However, the ISO recommends that this
"small difference" between inner eye temp and body temp be accounted
for by adjusting the "threshold temperature", i.e. the specific
temperature at which the system alarms.
IEC says A
high temp reading cannot be automatically considered a fever, and must be
confirmed with a clinical thermometer, it should conform to a separate
standard, ISO 80601-2-56.
The ISO/TR
13154:2017 and IEC 80601-2-59:2017 standards specifically state
that fever screening is deployed under indoor conditions:
[IEC] screening
thermographs have been used at ports-of-entry, ports-of exit and the entrances
to buildings under indoor environmental conditions with the intention
of separating febrile from afebrile individuals to help prevent the spread of
communicable diseases
[ISO] this
document provides general guidelines for the deployment, implementation and
operation of a screening thermograph intended to be used for non-invasive
febrile temperature screening of individuals under indoor environmental
conditions to prevent the spread of infection.
IEC says
the responsible organization needs to be aware of the type of lighting used at
the screening area. Lighting such as incandescent, halogen, quartz tungsten
halogen and other type of lamps that produce significant interference (heat)
should be avoided. The area chosen for screening should have a non-reflective
background and minimal reflected infrared radiation from the surroundings. IEC
recommends A/C drafts be diffused to ensure they are not blowing onto people
and cooling them. ISO adds that "sun-facing windows, radiant heaters, or
sources of cold (cold windows or outside walls" can also
"interfere" with accurate readings and must be avoided as well.
ISO states
that Controlling ambient temperature is important, as overly hot/cold people
will not give accurate results, particularly if they are sweating, “individuals
being screened should not be too cold or too hot and especially not sweating”.
ISO states
that the temperatures measured by a screening thermograph can be influenced when
the individual being screened is sweating. Sweating thresholds can vary
according to a person’s fitness level, environment of residence, length of
adaptation and the relative humidity. When humidity is controlled, these
effects are minimized. To produce consistent and reliable results of the
temperature screening process, it is imperative that the screening
thermograph be situated in a reserved stable indoor environment with a
temperature range of 20 °C to 24 °C and relative humidity range from 10 % to 50
%.
ISO states
one way to achieve such conditions would a be a special walk-through booth. In
order to prevent "cross-contamination" (febrile individuals in the
line infecting others), the ISO recommends that a "secondary screening
area" be set up "removed from the general traffic flow" for
people who are being confirmed for fever. The secondary screening area should
be properly equipped with "masks, wipes, disinfectants”. The secondary
screening area is a care area that should equipped with a clinical thermometer
and accessories that comply with ISO 80601-2-56 and should be staffed by
qualified medical personnel. The secondary screening area should be equipped
with sanitation supplies, e.g. masks, wipes, disinfectants. To prevent
cross-contamination, the secondary screening area should be positioned to allow
patient removal from the facility or to quarantine with reasonable privacy and
with minimum exposure to others (maintaining crosscontamination prevention).
ISO says
bathrooms should not be near screening areas. Toilets should not be proximal to
the screening thermograph area. This is to both inhibit potential
cross-infection and to prevent facial washing (alteration of the thermal
profile) immediately prior to entering the screening thermograph area.
ISO says the
backdrop behind the individual being screened and, where utilized, side screens
should be — thermally uniform, — non-reflective in the IR spectrum, and — not
dark in colour in the visible spectrum (closer to white than black).
ISO
recommends a single file line, and that people should "stop and
pause". However, ISO does state that at high-volume situations, the system
can operate in "near real time". To minimize disruption in high
volume situations, the response time and throughput of the screening
thermograph should be capable of operating in near real time for rapid and
effective screening. This can necessitate that the screening thermograph be
highly automated. But in low-volume scenarios, it's still best to ask people to
stand still.
ISO recommends
the responsible organization should retain this information(data) for at least
one month (normal maximum incubation time for known infectious diseases). The
responsible organization should be prepared to maintain the data for longer
periods when deemed necessary by the public health authorities and other
organizations ensuring protection of public safety.
Technically,
the GDPR does not apply to thermal camera readings, as it only
deals with the "processing of personal data" i.e. data that can
identify a specific person - which thermal readings cannot.
Vaporized hydrogen peroxide injections
On the more aggressive end of the spectrum for room
sterilization technologies is the injection of vaporized hydrogen peroxide
directly into the space. Hydrogen peroxide is a potent sterilizing agent that
has been used to decontaminate buildings infected with a range of biological
contaminants from anthrax spores to exotic viruses. The process is performed by
injecting vaporized hydrogen peroxide into a sealed vacant space and is usually
used more as an intentional sterilization procedure rather than a routine part
of normal building operation.
Disadvantages
• Requires pre-cleaning of all surfaces before
disinfecting.
• Not practical for wide disinfection of
occupied/finished spaces like office buildings or schools.
• Not for human use.
Advantage
• Highly effective at destroying microorganisms like
mold, bacteria and germs.
As a society, our awareness of how quickly potential
pathogens can spread has increased dramatically in just the span of a few
months. We understand the importance of human health and furthermore, we
understand that our economic livelihood as individuals, as a nation and even as
a world depends greatly on our ability to move about freely without concern for
the spread of infection.
Find more resources at
www.csemag.com
https://www.iso.org/standard/69346.html
https://www.iso.org/standard/69347.html
https://www.iso.org/standard/67348.html
https://ipvm.com/reports/fda-new