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Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic?

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This study examined homemade masks as an alternative to commercial face masks. Several household materials were evaluated for the capacity to block bacterial and viral aerosols. Twenty-one healthy volunteers made their own face masks from cotton t-shirts; the masks were then tested for fit. The number of microorganisms isolated from coughs of healthy volunteers wearing their homemade mask, a surgical mask, or no mask was compared using several air-sampling techniques. The median-fit factor of the homemade masks was one-half that of the surgical masks. Both masks significantly reduced the number of microorganisms expelled by volunteers, although the surgical mask was 3 times more effective in blocking transmission than the homemade mask. Our findings suggest that a homemade mask should only be considered as a last resort to prevent droplet transmission from infected individuals, but it would be better than no protection. (Disaster Med Public Health Preparedness. 2013;0:1-6).
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TestingtheEfficacyofHomemadeMasks:WouldTheyProtectinan
InfluenzaPandemic?
AnnaDavies,KatyAnneThompson,KarthikaGiri,GeorgeKafatos,JimmyWalkerandAllanBennett
DisasterMedicineandPublicHealthPreparedness/FirstViewArticle/July2013,pp16
DOI:10.1017/dmp.2013.43,Publishedonline:22May2013
Linktothisarticle:http://journals.cambridge.org/abstract_S1935789313000438
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AnnaDavies,KatyAnneThompson,KarthikaGiri,GeorgeKafatos,JimmyWalkerandAllanBennettTestingtheEfficacy
ofHomemadeMasks:WouldTheyProtectinanInfluenzaPandemic?.DisasterMedicineandPublicHealth
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ORIGINAL RESEARCH
Testing the Efficacy of Homemade Masks: Would
They Protect in an Influenza Pandemic?
Anna Davies, BSc, Katy-Anne Thompson, BSc, Karthika Giri, BSc, George Kafatos, MSc,
Jimmy Walker, PhD, and Allan Bennett, MSc
ABSTRACT
Objective: This study examined homemade masks as an alternative to commercial face masks.
Methods: Several household materials were evaluated for the capacity to block bacterial and viral aerosols.
Twenty-one healthy volunteers made their own face masks from cotton t-shirts; the masks were then tested
for fit. The number of microorganisms isolated from coughs of healthy volunteers wearing their homemade
mask, a surgical mask, or no mask was compared using several air-sampling techniques.
Results: The median-fit factor of the homemade masks was one-half that of the surgical masks. Both
masks significantly reduced the number of microorganisms expelled by volunteers, although the
surgical mask was 3 times more effective in blocking transmission than the homemade mask.
Conclusion: Our findings suggest that a homemade mask should only be considered as a last resort to
prevent droplet transmission from infected individuals, but it would be better than no protection.
(Disaster Med Public Health Preparedness. 2013;0:1–6)
Key Words: homemade facemasks, respirators, airborne transmission, microbial dispersion, pandemic
prevention
Wearing a face mask in public areas may
impede the spread of an infectious disease
by preventing both the inhalation of
infectious droplets and their subsequent exhalation
and dissemination. In the event of a pandemic
involving an airborne-transmissible agent, the general
public will have limited access to the type of high-
level respiratory protection worn by health care
workers, such as N95 respirators. Images of members
of the public wearing surgical masks were often used
to illustrate the 2009 H1N1 flu pandemic. However,
the evidence of proportionate benefit from widespread
use of face masks is unclear.
A recent prospective cluster-randomized trial compar-
ing surgical masks and non-fit-tested P2 masks (filters
at least 94% of airborne particles) with no mask use in
the prevention of influenza-like illness. The findings
of the study found that adherence to mask use
significantly reduced (95% CI, 0.09-0.77; P5.015)
the risk for infection associated with influenza-like
illness, but that less than 50% of participants wore
masks most of the time.
1
Facemasks may prevent
contamination of the work space during the outbreak
of influenza or other droplet-spread communicable
disease by reducing aerosol transmission. They may
also be used to reduce the risk of body fluids, including
blood, secretions, and excretions, from reaching the
wearer’s mouth and nose.
To date, studies on the efficacy and reliability of face
masks have concentrated on their use by health care
workers. Although health care workers are likely to
be one of the highest risk groups in terms of exposure,
they are also more likely to be trained in the use of
masks and fit tested than the general public. Should
the supply of standard commercial face masks not
meet demand, it would be useful to know whether
improvised masks could provide any protection to
others from those who are infected.
METHODS AND MATERIALS
In this study, common household materials(see
Table 1) were challenged with high concentrations
of bacterial and viral aerosols to assess their filtration
efficiencies. Surgical masks have been considered the
type of mask most likely to be used by the general
public, and these were used as a control. The pressure
drop across each of the materials was measured to
determine the comfort and fit between face and mask
that would be needed to make the material useable in
mask form. We devised a protocol for constructing a
‘‘homemade’’ mask, based on the design of a surgical
mask, and volunteers were invited to make their own
masks. These were then quantitatively fit tested. To
determine the effect of homemade and surgical masks
in preventing the dispersal of droplets and aerosol
particles produced by the wearer, the total bacterial
Disaster Medicine and Public Health Preparedness 1
Copyright &2013 Society for Disaster Medicine and Public Health, Inc. DOI: 10.1017/dmp.2013.43
count was measured when the volunteers coughed wearing
their homemade mask, a surgical mask, and no mask.
Testing the Filtration Efficiency
A range of common household materials were tested, together
with the material from a surgical mask (Mo
¨lnlycke Health Care
Barrier face mask 4239, EN14683 class I), for comparison.
Circular cutouts of the tested materials were placed without
tension in airtight casings, creating a ‘‘filter’’ in which the
material provided the only barrier to the transport of the aerosol.
A Henderson apparatus allows closed-circuit generation of
microbial aerosols from a Collison nebulizer at a controlled
relative humidity. This instrument was used to deliver the
challenge aerosol across each material at 30 L/min using
the method of Wilkes et al,
2
which is about 3 to 6 times per
minute the ventilation of a human at rest or doing light work,
but is less than 0.1 the flow of an average cough.
Downstream air was sampled simultaneously for 1 minute into
10 ml of phosphate buffer manucol antifoam using 2 all-glass
impingers. One impinger sampled the microorganisms that
had penetrated through the material filter, while the other
sampled the control (no filter). The collecting fluid was
removed from the impingers and assayed for microorganisms.
This test was performed 9 times for each material. The
filtration efficiency (FE) of the fabric was calculated using the
following formula (cfu indicate colony-forming units):
FE ¼Upstream cfu Downstream cfu 100
Upstream cfu
The pressure drop across the fabric was measured using a
manometer (P200UL, Digitron), with sensors placed on
either side of the filter casing, while it was challenged with a
clean aerosol at the same flow rate.
Microorganisms
Two microorganisms were used to simulate particle challenge:
Bacillus atrophaeus is a rod-shaped spore-forming bacterium
(0.95-1.25 mm) known to survive the stresses caused by
aerosolization.
3
The suspension was prepared from batches
previously prepared by the Health Protection Agency, Centre
for Emergency Preparedness and Response Production Division.
4
Each material was challenged with approximately 10
7
cfu
B atrophaeus.
Bacteriophage MS2 (MCIMB10108) is a nonenveloped
single-stranded RNA coliphage, 23 nm in diameter, known
to survive the stresses of aerosolization.
5
Each material was
challenged with approximately 10
9
plaque-forming units
(pfu) of bacteriophage MS2.
The two test organisms can be compared in size to influenza
virus, which is pleomorphic and ranges from 60 to 100 nm;
Yersinia pestis, which is 0.75 mm; Banthracis,which is 1 to
1.3 mm; Francisella tularensis, which is 0.2 mm; and Mycobacterium
tuberculosis, which is 0.2 to 0.5 mm.
6
Bacteriophage MS2 and
B atrophaeus were chosen as the test organisms to represent
influenza virus. This decision was made not only because of the
lower risks of associated infection but also because the work
would be technically easier to carry out using an Advisory
Committee on Dangerous Pathogens (ACDP) class 1 organism
versus an ACDP class 2 organism influenza.
Making the Face Mask
For this study, 21 healthy volunteers were recruited, 12 men
and 9 women. The participants were aged between 20 and
44 years; the majority was in the 20- to 30-year age range.
Each volunteer made a homemade face mask following a
protocol devised by the authors. All face masks were made
with 100% cotton t-shirt fabric using sewing machines to
speed construction. A surgical mask (Mo
¨lnlycke Health Care
TABLE 1
Filtration Efficiency and Pressure Drop Across Materials Tested with Aerosols of Bacillus atrophaeus and Bacteriophage
MS2 (30 L/min)
a
Material
B atrophaeus Bacteriophage MS2 Pressure Drop Across Fabric
Mean % Filtration Efficiency SD Mean % Filtration Efficiency SD Mean SD
100% cotton T-shirt 69.42 (70.66) 10.53 (6.83) 50.85 16.81 4.29 (5.13) 0.07 (0.57)
Scarf 62.30 4.44 48.87 19.77 4.36 0.19
Tea towel 83.24 (96.71) 7.81 (8.73) 72.46 22.60 7.23 (12.10) 0.96 (0.17)
Pillowcase 61.28 (62.38) 4.91 (8.73) 57.13 10.55 3.88 (5.50) 0.03 (0.26)
Antimicrobial Pillowcase 65.62 7.64 68.90 7.44 6.11 0.35
Surgical mask 96.35 0.68 89.52 2.65 5.23 0.15
Vacuum cleaner bag 94.35 0.74 85.95 1.55 10.18 0.32
Cotton mix 74.60 11.17 70.24 0.08 6.18 0.48
Linen 60.00 11.18 61.67 2.41 4.50 0.19
Silk 58.00 2.75 54.32 29.49 4.57 0.31
a
Numbers in parentheses refer to the results from 2 layers of fabric.
Are Homemade Masks Effective?
Disaster Medicine and Public Health Preparedness2
Barrier face mask 4239, EN14683 class I) was used as
a control. Also, all volunteers completed a questionnaire
indicating their opinions of mask wearing.
Determining the Fit Factor of the Mask
A commercial fit test system (TSI PortaCount Plus Respirator
Fit Tester and N95- Companion Module model 8095) was
used to measure respirator fit by comparing the concentration
of microscopic particles outside the respirator with the
concentration of particles that have leaked into the respirator.
The ratio of these 2 concentrations is known as the fit factor.
To conduct the fit test, the apparatus was set up and operated
according to the manufacturer’s instructions.
Volunteers were instructed to fit their surgical and homemade
face masks with no help or guidance from the operator; to
ensure that the mask was comfortable for 2 minutes; the
participants were given time to purge any particles trapped
inside the mask. The fit test was then conducted with
volunteers performing the following consecutive exercises,
each lasting 96 seconds: (1) normal breathing, (2) deep
breathing,
7
(3) head moving side to side, (4) head moving up
and down, (5) talking aloud (reading a prepared paragraph),
(6) bending at the waist as if touching their toes, and
(7) normal breathing.
Determining the Effect of Masks in Preventing the
Dispersal of Droplets and Aerosol
An enclosed 0.5-m
3
mobile sampling chamber, or cough box,
which was constructed for the purpose of sampling aerosols and
droplets from healthy volunteers (PFI Systems Ltd, Milton
Keynes), was placed in a 22.5-m
3
high-frequency particulate
air-filtered environmental room. Four settle plates were placed
in the cough box to sample for droplets, together with a 6-stage
Andersen sampler to sample and separate small particles.
8
A Casella slit-air sampler
9
was also attached to the cough box.
Tryptose soya agar was used as the culture medium. Volunteers
wearing protective clothing (Tyvek suits) coughed twice into
the box, and the air inside was sampled for 5 minutes. Each
volunteer was sampled 3 times: wearing the homemade mask,
the surgical mask, and no mask. The air within the cough box
was high-frequency particulate air filtered for 5 minutes
between each sample to prevent cross-contamination between
samples. The plates were incubated for a minimum of 48 hours
at 378C before counting.
Statistical Analysis
To evaluate the face mask fit, the median and interquartile
range were calculated for each exercise and face mask for
the 21 individuals. Wilcoxon sign rank tests were used to
compare the masks. The same approach was used to
determine differences between the different mask types
and their efficacy in preventing dissemination of droplets
and particles
RESULTS
Filtration Efficacy
All the materials tested showed some capability to block
the microbial aerosol challenges. In general, the filtration
efficiency for bacteriophage MS2 was 10% lower than for
B atrophaeus (Table 1). The surgical mask had the highest
filtration efficiency when challenged with bacteriophage
MS2, followed by the vacuum cleaner bag, but the bag’s
stiffness and thickness created a high pressure drop across
the material, rendering it unsuitable for a face mask. Simi-
larly, the tea towel, which is a strong fabric with a thick
weave, showed relatively high filtration efficiency with both
B atrophaeus and bacteriophage MS2, but a high pressure
drop was also measured.
The surgical mask (control) showed the highest filtration
efficiency with B atrophaeus. Also, as expected, its measured
low pressure drop showed it to be the most suitable material
among those tested for use as a face mask. The pillowcase and
the 100% cotton t-shirt were found to be the most suitable
household materials for an improvised face mask. The slightly
stretchy quality of the t-shirt made it the more preferable
choice for a face mask as it was considered likely to provide a
better fit.
Although doubling the layers of fabric did significantly
increase the pressure drop measured across all 3 materials
(P,.01 using Wilcoxon sign rank test), only the 2 layers of
tea towel material demonstrated a significant increase in
filtration efficiency that was marginally greater than that of
the face mask.
In the questionnaire on mask use during a pandemic,
6 participants said they would wear a mask some of the time,
6 said they would never wear a mask, and 9 either did not
know or were undecided. None of the participants said that
they would wear a mask all of the time. With 1 exception, all
participants reported that their face mask was comfortable.
However, the length of time each participant kept their mask
on during testing was minimal (15 min), and with long-term
wear, comfort might decrease.
Facemask Fit Testing
A Wilcoxon sign rank test showed a significant difference
between the homemade and surgical mask for each exercise
and in total (all tests showed P,.001). The median and
interquartile range for each mask and exercise are given in
Table 2.
Prevention of Droplet and Particle Dissemination
When Coughing
Results from the cough box experiments showed that both
the surgical mask and the homemade mask reduced the total
number of microorganisms expelled when coughing (P,.001
and P5.004, respectively; see Table 3).
Are Homemade Masks Effective?
Disaster Medicine and Public Health Preparedness 3
On analyzing the effect of mask wearing in reducing the
number of microorganisms isolated from the Anderson air
sampler (Table 4), the surgical mask was found to be
generally more effective in reducing the number of micro-
organisms expelled than the homemade mask, particularly at
the lowest particle sizes. The number of microorganisms
isolated from the coughs of healthy volunteers was generally
low, although this varied according to the individual sampled
(Table 3). It is possible, therefore, that the sampling
limitations negatively affected the statistical analysis.
Pearson x
2
tests comparing the proportion of particles greater
than 4.7 mm in diameter and particles less than 4.7mmin
diameter found that the homemade mask did not significantly
reduce the number of particles emitted (P5.106). In contrast,
the surgical mask did have a significant effect (P,.001).
DISCUSSION
Facemasks reduce aerosol exposure by a combination of the
filtering action of the fabric and the seal between the mask
and the face. The filtration efficiency of the fabric depends
on a variety of factors: the structure and composition of the
fabric, and the size, velocity, shape, and physical properties of
the particles to which it is exposed.
10
Although any material
may provide a physical barrier to an infection, if as a mask it
does not fit well around the nose and mouth, or the material
freely allows infectious aerosols to pass through it, then it will
be of no benefit.
The test organisms in this study can be used to estimate
the efficacy of these masks against influenza virus because
essentially any aerosolized particle will behave predominately
in the air as a result of its physical characteristics rather than
its biological properties (ie, influenza virus particles will travel
in the air in the same manner as particles of an equivalent
size). Therefore, as we have tested a viral pathogen smaller
than influenza and a bacterial pathogen larger than influenza,
we have tested the face masks with a suitable challenge across
the size range of influenza virus particles. Furthermore, the
data from this study could also be applied to other organisms
within this size range that are potentially transmitted via the
aerosol route.
Quantitative fit testing can only estimate the combined
effects of filtration efficiency and goodness of fit. Although
sensitive to particles with diameters as small as 0.02 mm, it is
not sensitive to variations in particle size, shape, composition,
or refractive index. As a result, this method of fit testing
does not allow the distinction between true bioaerosols and
droplet contamination.
A study conducted in the Netherlands using a commercial
fit-test system (Portacount Plus Respirator Fit Tester) on
volunteers wearing both improvised masks made from tea
cloths and surgical masks over a 3-hour period found results
similar to those found in this study.
11
The authors
demonstrated a median protection factor of between 2.2
and 2.5 for various activities when wearing a mask with a tea
TABLE 2
Median and Interquartile Range Results from
Respirator Fit Testing of Homemade and Surgical
Masks
Median Interquartile Range
Condition Homemade Mask Surgical Mask
Normal breathing 2.0 (2.0, 2.5) 6.0 (2.5, 9.0)
Heavy breathing 2.0 (2.0, 3.0) 7.0 (2.5, 13.5)
Head moving side to side 2.0 (1.0, 2.0) 5.0 (3.0, 7.0)
Head moving up and down 2.0 (1.5, 2.0) 5.0 (3.0, 7.0)
Bending over 1.0 (1.0, 2.0) 3.0 (2.0, 9.0)
Talking 2.0 (1.0, 2.0) 6.0 (3.0, 12.0)
Normal 2.0 (1.0, 2.0) 5.0 (2.0, 8.5)
All data 2.0 (1.0, 2.0) 5.0 (3.0, 9.0)
TABLE 3
Median Colony-Forming Units by Sampling Method
Isolated From Volunteers Coughing When Wearing a
Surgical Mask, a Homemade Mask, and No Mask
Median Interquartile Range
Sampling Method No Mask Homemade Mask P
Air 6.0 (1.0, 26.5) 1.0 (0.5, 6.5) .007
Settle plates 1.0 (0.0, 3.0) 1.0 (0.0, 2.0) .224
Total 2.0 (0.0, 12.3) 1.0 (0.0, 3.0) .004
Median Interquartile Range
Sampling Method No Mask Surgical Mask P
Air 6.0 (1.0, 26.5) 1.0 (0.5, 3.0) .002
Settle plates 1.0 (0.0, 3.0) 0.0 (0.0, 0.0) .002
Total 2.0 (0.0, 12.3) 0.0 (0.0, 1.0) ,.001
TABLE 4
Total Colony-Forming Units Isolated by Particle Size
From 21 Volunteers Coughing When Wearing a
Surgical Mask, Homemade Mask, and No Mask
Particle Diameter, mm No Mask Homemade Mask Surgical Mask
.7935
4.7-7 18 7 7
3.3-4.7 5 4 4
2.1-3.3 47 7 5
1.1-2.1 100 16 6
0.65-1.1 21 6 3
Total 200 43 30
Are Homemade Masks Effective?
Disaster Medicine and Public Health Preparedness4
towel filter and protection factors of between 4.1 and 5.3
for the surgical mask. It was interesting that the study also
found that median protection factors increased over the
3-hour period for those wearing the homemade masks,
decreased for those wearing filtering face piece (FFP2) masks
that lower the wearer’s exposure to airborne particles by a
factor of 10, and showed no consistent pattern for those
wearing a surgical mask.
11
The materials used in this published study were fresh and
previously unworn. It is likely that materials conditioned
with water vapor, to create a fabric similar to that which has
been worn for a couple of hours, would show very different
filtration efficiencies and pressure drops. In contrast, a study
of breathing system filters found a greater breakthrough of
bacteriophage MS2 on filters that had been preconditioned.
Although the droplet sizes for both virus and bacteria were
the same and affected the filter media in a similar manner, it
was suggested that the viruses, after contact with the moisture
on the filter, were released from their droplet containment,
and driven onward by the flow of gas.
12
The average concentration of Streptococcus organisms in
saliva has been estimated to be 6.7 310
7
cfu/mL,
13
which
is higher than that of influenza viruses in inoculated
volunteers.
14
Therefore, the number of oral microorganisms
isolated may well provide an indication of the concentration
of influenza being shed. Results from the cough box
demonstrated that surgical masks have a significant effect in
preventing the dispersal of large droplets and some smaller
particles when healthy volunteers coughed. The homemade
mask also prevented the release of some particles, although
not at the same level as the surgical mask. The numbers
of microorganisms isolated from the coughs of healthy
volunteers was in general very low, and it is likely that had
we used volunteers with respiratory infections, the homemade
mask may have shown a more significant effect in preventing
the release of droplets.
It was observed during this study that there was greater
variation among volunteers in their method of fitting the
surgical mask. The need to tie the straps at the back of the
head meant that the surgical mask was fit in a variety of ways.
In contrast, the face mask had looped elastic straps that were
easier for the volunteer to fit.
Comfort should be an important factor in the material used to
make a homemade mask. The pressure drop across a mask is a
useful measure both of resistance to breathing and the
potential for bypass of air around the filter seal. If respiratory
protection is not capable of accommodating the breathing
demands of the wearer, then the device will impose an extra
breathing load on the wearer, which is especially impractic-
able for people with breathing difficulties. Furthermore,
the extra breathing load may induce leakage owing to the
increased negative pressure in the face mask.
15
In practice, people will not wear an uncomfortable mask for
a long period; even if they do, it is unlikely that they will
wear the mask properly. During the outbreak of severe acute
respiratory syndrome, an account of a flight from Bangkok,
Thailand, to Manchester, England. described mask wearers
removing their mask to cough, sneeze, and wipe their nose
(not necessarily into a handkerchief) and to sort through the
communal bread basket.
16
For those who wear a mask for
necessity, such as health care workers, regular training and fit
testing must be emphasized. Whereas, for those who choose
to wear a homemade mask, the requirements of cleaning and
changing the mask should be highlighted. Most importantly,
the lower protective capabilities of a homemade mask should
be emphasized so that unnecessary risks are not taken.
CONCLUSION
A protective mask may reduce the likelihood of infection, but
it will not eliminate the risk, particularly when a disease has
more than 1 route of transmission. Thus any mask, no matter
how efficient at filtration or how good the seal, will have
minimal effect if it is not used in conjunction with other
preventative measures, such as isolation of infected cases,
immunization, good respiratory etiquette, and regular hand
hygiene. An improvised face mask should be viewed as the
last possible alternative if a supply of commercial face masks is
not available, irrespective of the disease against which it may
be required for protection. Improvised homemade face masks
may be used to help protect those who could potentially, for
example, be at occupational risk from close or frequent
contact with symptomatic patients. However, these masks
would provide the wearers little protection from microorgan-
isms from others persons who are infected with respiratory
diseases. As a result, we would not recommend the use of
homemade face masks as a method of reducing transmission
of infection from aerosols.
About the Authors
Public Health England (HPA), Porton Down Salisbury (Dr Walker, Miss Thompson,
Davies and Giri, and Mr Bennett); PHE, Colindale, London (Mr Kafatos),
United Kingdom.
Address correspondence and reprint requests to Jimmy Walker, PhD, PHE, Porton
Down, Salisbury, SP4 0JG UK (e-mail: jimmy.walker@phe.gov.uk).
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Are Homemade Masks Effective?
Disaster Medicine and Public Health Preparedness6
... Whereas, the limited supply at the peak of the outbreak exacerbated the shortage of masks. In the face of the exponentially growing number of new cases, some countries began to encourage the public to use homemade masks that were made of common materials for self-protection (Davies et al. 2013). However, except for N95 masks, the public have always doubt the efficacy of surgical and homemade masks, because the National Institute for Occupational Safety and Health (NOISH) regulated the 0.30 μm particle diameter filtering efficiency as the basis to evaluate the performance of masks; thus, some people pointed out the ordinary masks cannot block exhaled virus droplets of small particle size, and thus wearing masks cannot reduce the risk of infection. ...
... person)) 28.8 Wells-Riley model and give scientific mask-wearing suggestions under different conditions. In order to detect the protection levels of several common masks, we reviewed and analyzed the experimental research results of N95, surgical, and homemade masks according to the four papers (Davies et al. 2013;Lee et al. 2008;Noti et al. 2012;Weber et al. 1993), and used filtration efficiency as the indicator, obtaining the efficiency distribution characteristics along with different particle sizes of the masks, as depicted in Fig. 3. ...
... However, it is undeniable that various types of masks can achieve the blocking effect of exhaled droplets to different degrees. The filtering efficiency of N95 masks remained stable above 98% (Lee et al. 2008;Noti et al. 2012), surgical masks ranged from 75 to 93% (Davies et al. 2013;Lee et al. 2008;Noti et al. 2012). Even homemade masks can have a filtering efficiency of 71-82%. ...
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Public transport is a fundamental service for the resumption of work and production, but the enclosed environment and dense population create very favorable conditions for the spread of epidemic infections. Thus, effective public health interventions are urgently introduced. The objective of this paper is to quantitatively estimate the SARS-CoV-2 transmission probability and evaluate the influence of environmental parameters and individual intervention on the epidemic prevention. For this purpose, (1) we estimate the virus emission rate with Diamond Princess Cruise Ship infection data by Monte Carlo simulation and the improved Wells-Riley model, and (2) employ the reproductive number R to quantify diverse mitigation strategies. Different determinants are examined such as the duration of exposure, the number of passengers combined with individual interventions such as mask type and mask-wearing rate. The results show that the SARS-CoV-2 quantum generation rate is 185.63. The R shows a stronger positive correlation with the exposure time comparing to the number of passengers. In this light, reducing the frequency of long-distance journeys on crowded public transportation may be required to reduce the spread of the virus during the pandemic. N95 mask and surgical mask can reduce the transmission risk by 97 and 84%, respectively, and even homemade mask can reduce the risk by 67%, which indicates that it is necessary to advocate wearing masks on public transportation.
... Prior works on improvised materials found that common fabrics (sweatshirts, t-shirts, towels and scarfs) can block 10-60% percent of particles in the 0.2-1 mm range (Rengasamy, Eimer, and Shaffer 2010) and improves to 90% for the larger particle ranges (>1 mm) due to being in the inertial impaction regime (Konda et al. 2020). Other studies have since examined various non-fabric filters, including HVAC filters, vacuum bags, tea towels, and sterilization wraps (300-wt) and found filtrations of between <60-87% at 0.3 um, 5-75% at 0.3 um, 36% at 2.75 um and 95% at 2.75 um, respectively Rogak et al. 2020;Davies et al. 2013). ...
... Though trends were not readily visible, a recent study by Kondo et al. suggested that cotton performs better at higher thread count (Konda et al. 2020). The FE of these fabrics increased with increasing particle size because the capture physics are in the inertial impaction and interception regime (Konda et al. 2020;Davies et al. 2013;Rengasamy, Eimer, and Shaffer 2010;Hinds 1999). Similar trends were also observed when the cotton fabric was tested in doublelayers ( Figure 3). ...
... Nonetheless, these materials will have lower FE and lower pressure drop due to the leakage. The work of Davies et al. (2013) establish that procedure masks have a leakage of about 20% and improvised masks will likely be worse. ...
Article
The goal of this study is to evaluate the filtration efficiency and breathability of improvised filtration and commonly available mask materials, as well as to assess their reusability. Materials readily available to the general public such as cotton, fragrance and additive-free dry baby cleaning wipes, and those abundantly available in the hospital setting, such as sterilization wraps, were chosen for testing, amongst others. In the COVID-important 2–5 μm particle range, two-layers of cotton provided filtration efficiency between 34%–66%. Amongst potential filter materials, 300-weight sterilization wraps provided approximately 80% filtration efficiency and are readily available in the healthcare setting. The addition of sterilization wrap to cotton fabrics brought the filtration efficiency to above that of the sterilization wrap (80%-90%) at the expense of added pressure drop. Four-layers of dry baby wipes performed very well with a filtration efficiency of 85% and a reasonable pressure drop (1/3 of procedure mask). Since the material is advertised as pure spunlace polypropylene and designed to contact the skin during cleaning, it would appear generally safe as a filter insert. Of improvised filters, polypropylene electrostatic HVAC filters performed the best with filtration efficiencies of >99%, but are not recommended due to the risk of confusion with glass-based HVAC filters and uncertainty regarding trace materials used in the filter. The filtration efficiency of two-layers of cotton fabrics with one-layer of sterilization wrap slightly improved over 10 laundry cycles, while the performance of other non-wovens, like dry baby wipes, degraded more rapidly and should be considered disposable. In summary, we found that two-layers of cotton fabric can provide a comfortable, breathable and reusable option. The addition of a sterilization wrap or four-layers of pure spunlace fragrance free dry baby wipes can significantly improve filtration and block expiratory aerosols at the expense of an added pressure drop.
... Reference [15] indicates that masks are recommended for people when they are in areas of widespread transmission and they cannot guarantee a distance of at least one meter from others. Reference [16] concluded that masks remarkably reduced the number of microorganisms expelled by volunteers. Reference [17] studied the ef ciency of aerosol ltration fabrics in cloth masks. ...
... The viral emission rate for infected humans (Q I ) was estimated from models of respiration and inference from a documented super spreading event (Miller et al., 2020). The effectiveness of face coverings in reducing emission, including N95 masks, surgical masks, cloth masks, and face shields, was estimated from studies that quantified the filtration efficiencies (Davies et al., 2013;Lindsley et al., 2014;Long et al., 2020). The typical sensitivity and sensitivity of RT-PCR tests for SARS-CoV-2 were estimated from several meta-analyses of current tests (Arevalo-Rodriguez et al., 2020;Watson et al., 2020). ...
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The virus that causes COVID‐19 likely evolved in a mammalian host, possibly Old‐World bats, before adapting to humans, raising the question of whether reverse zoonotic transmission to bats is possible. Wildlife management agencies in North America are concerned that the activities they authorize could lead to transmission of SARS‐CoV‐2 to bats from humans. A rapid risk assessment conducted in April 2020 suggested that there was a small but significant possibility that SARS‐CoV‐2 could be transmitted from humans to bats during summer fieldwork, absent precautions. Subsequent challenge studies in a laboratory setting have shed new information on these risks, as has more detailed information on human epidemiology and transmission. This inquiry focuses on the risk to bats from winter fieldwork, specifically surveys of winter roosts and handling of bats to test for white‐nose syndrome or other research needs. We use an aerosol transmission model, with parameter estimates both from the literature and from formal expert judgment, to estimate the risk to three species of North American bats, as a function of several factors. We find that risks of transmission are lower than in the previous assessment and are notably affected by chamber volume and local prevalence of COVID‐19. Use of facemasks with high filtration efficiency or a negative COVID‐19 test before field surveys can reduce zoonotic risk by 65 to 88%.
... 28 Studies have evaluated the relative effectiveness of different materials for constructing non-medical grade masks. 29 This evidence can be used to choose facial coverings to optimize their efficacy. Effectiveness, however, depends not just on filtration efficacy but also on factors such as comfort, fit, and breathability to optimize compliance. ...
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The world continues to face an unprecedented threat from the COVID-19 pandemic. Physical distancing has been identified as one of the methods of reducing transmission. As a result, businesses, schools, and institutes of education were closed due to such measures as well as restrictions on travel and social gatherings. Working from home, telework, and on-line meetings are now the norm. As businesses have reopened, they will be looking for guidance on how to work safely. Even those sectors that have continued to function will need guidance to ramp up functioning to new levels of normalcy. This document is intended to provide return-to-work guidance for both employers and the OEM physicians who will be supporting businesses to implement safe return-to-work strategies.
... [6] Evidence of the effectiveness of the cloth mask arises mainly from in vitro filtration studies, which showed that cloth masks may offer some protection from respiratory pathogens, despite substantially lower filtration ability compared with surgical masks. [7] Factors that may affect filtration include cloth type, stretching and the manner of mask washing. [8] In a simulation study assessing prevention of airborne particle expulsion, cloth masks offered marginal protection, with substantially better protection offered by medical masks. ...
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