the sample pathogen was not SARS-CoV-1. Nevertheless,
the results of the literature review conducted here are in
close agreement with those studies and reinforces the CDC
However, the expression of UVGI effectiveness in terms
of dosage may be too much of an abstraction for some
readers. The approximation in (6) provides readers with a
tool to evaluate the effectiveness of a simple UVGI system
based on bulb wattage and distance to the sample surface
without the need for complex instrumentation. The target
dosage D= 36144 J/m2derived here has been shown to
inactivate 99.999% (≥5-log) of SARS-CoV-1 contaminants in
the minimum CDC recommendation of D= 10000 J/m2.
A. Limitations of UVGI
As a number of studies have noted, there are many factors
that can impede UVGI ability in practice , . For
N95 respirator disinfection applications, there are signiﬁcant
concerns as to whether UVGI systems can deliver the sufﬁcient
dosage to inactivate viral particles trapped within the ﬁbers of
the mask surface . Shadowing effects must also be taken
into consideration when designing UVGI systems .
It is important to note that while  demonstrated a 5-
log reduction in SARS-CoV-1 concentration, this should not
be taken to mean that sterilized surfaces no longer pose an
infectivity threat. For surfaces containing extremely highviral
loads, for instance, 99.999% inactivation does not necessar-
ily translate to complete sterilization. In one recent study,
researchers reported SARS-CoV-2 viral loads (expressed in
copies/mL) from COVID-19 patient samples ranging from
641 to 1.34 ×1011 with a reported median of 7.52 ×105
. Supposing a surface is infected with the median value,
decrease the viral load to 100 copies/mL. However, taking the
upper bound of the dataset would still leave a viable residual
viral load of 106copies/mL.
While UVGI has been shown to reduce the risk of contact
transmission, more robust disinfection protocols can be de-
signed by implementing a multimodal approach that provides
redundancy if environmental factors do not allow for complete
UV-C inactivation. The CDC recommends the use of UVGI
methods in conjunction with vaporous hydrogen peroxide
treatment and moist heat . A well designed protocol that
uses UVGI in conjunction with other proven disinfection
methods can be a good way to manage and mitigate viral
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