How different masks work

Excerpt

Which mask works best? To visualise droplets and aerosols, UNSW researchers used LED lighting system & a high-speed camera, filming people coughing and sneezing in different scenarios — using no mask, two different types of cloth masks, and a surgical mask.

We confirmed that even speaking generates substantial droplets. Coughing and sneezing (in that order) generate even more. A three-ply surgical mask was significantly better than a one-layered cloth mask at reducing droplet emissions caused by speaking, coughing and sneezing, followed by a double-layer cloth face covering. A single-layer cloth face covering also reduced the droplet spread caused by speaking, coughing and sneezing but was not as good as a two-layered cloth mask or surgical mask.

We do not know how this translates to infection risk, which will depend on how many asymptomatic or mildly symptomatic infected people are around. However, it shows a single layer is not as good a barrier as a double layer.

MORE: UNSW

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Polypropylene bags – DIY mask

EDITOR’S NOTE: shopping bags made from this material are ubiquitous in Asia and Africa. The article states that ‘data shows that polypropylene bags are worse than surgical masks at capturing virus-sized particles. However, the high breathability of polypropylene bags means they can be layered up to make more effective DIY masks, although they still do not come close to the performance of a surgical mask.’

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Shadowgraph imaging of human exhaled airflows

Airflow patterns

Using a newly constructed airflow imaging system, airflow patterns were visualized that were associated with common, everyday respiratory activities (e.g. breathing, talking, laughing, whistling). The effectiveness of various interventions (e.g. putting hands and tissues across the mouth and nose) to reduce the potential transmission of airborne infection, whilst coughing and sneezing, were also investigated.  

From the digital video footage recorded, it was seen that both coughing and sneezing are relatively poorly contained by commonly used configurations of single-handed shielding maneuvers. Only some but not all of the forward momentum of the cough and sneeze puffs are curtailed with various hand techniques, and the remaining momentum is disseminated in a large puff in the immediate vicinity of the cougher, which may still act as a nearby source of infection.

The use of a tissue (in this case, 4-ply, opened and ready in the hand) proved to be surprisingly effective, though the effectiveness of this depends on the tissue remaining intact and not ripping apart. Interestingly, the use of a novel ‘coughcatcher’ device appears to be relatively effective in containing coughs and sneezes.

One aspect that became evident during the experimental procedures was that the effectiveness of all of these barrier interventions is very much dependent on the speed with which the user can put them into position to cover the mouth and nose effectively. From these qualitative schlieren and shadowgraph imaging experiments, it is clear that making some effort to contain one’s cough or sneeze puffs is worthwhile.

ORIGINAL SOURCE: PLOS One

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Prevention of COVID-19

Excerpt

There is currently no vaccine to prevent coronavirus disease 2019 (COVID-19). The best way to prevent illness is to avoid being exposed to this disease. However, as a reminder, CDC always recommends everyday preventive actions to help prevent the spread of respiratory diseases, including:

  • Avoid close contact with people who are sick.
  • Avoid touching your eyes, nose, and mouth.
  • Stay home when you are sick.
  • Cover your cough or sneeze with a tissue, then throw the tissue in the trash.
  • Clean and disinfect frequently touched objects and surfaces using a regular household cleaning spray or wipe.

Follow CDC’s recommendations for using a facemask.

  • CDC does not recommend that people who are well wear a facemask to protect themselves from respiratory diseases, including COVID-19.
  • Facemasks should be used by people who show symptoms of COVID-19 to help prevent the spread of the disease to  others. The use of facemasks is also crucial for health workers and people who are taking care of someone in close settings (at home or in a health care facility).

Wash your hands.

  • Wash your hands often with soap and water for at least 20 seconds, especially after going to the bathroom; before eating; and after blowing your nose, coughing, or sneezing.
  • If soap and water are not readily available, use an alcohol-based hand sanitizer with at least 60% alcohol. Always wash hands with soap and water if hands are visibly dirty.

SOURCE: CDC

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FAQ about respirators (e.g., masks) and their use

Equipment

Answers to your frequently asked questions:

What is a “respirator”?

A “respirator” is a personal protective device that is worn on the face or head and covers at least the nose and mouth. A respirator is used to reduce the wearer’s risk of inhaling hazardous airborne particles (including infectious agents), gases or vapors. Respirators, including those intended for use in healthcare settings, are certified by the CDC/NIOSH.

Should I wear a respirator in public?

CDC does not recommend the routine use of respirators outside of workplace settings (i.e, in the community). Most often, spread of respiratory viruses from person-to-person happens among close contacts (within 6 feet). CDC recommends everyday preventive actions to prevent the spread of respiratory viruses, such as avoiding people who are sick, avoiding touching your eyes or nose, and covering your cough or sneeze with a tissue. People who are sick should stay home and not go into crowded public places or visit people in hospitals. Workers who are sick should follow CDC guidelines and stay home when they are sick.

[ EDITOR’S NOTE: use of the term “respirator” as intended by the CRC resource has NOT consistently caught on in either American hospitals or in everyday language. “Respirator” in the CRC usage could mean anything from a simple (but well-sealing and higher quality) mask to a motor-driven filtering device. ]

What is an N95 filtering facepiece respirator (FFR)?

An N95 FFR is a type of respirator which removes particles from the air that are breathed through it. These respirators filter out at least 95% of very small (0.3 micron) particles. N95 FFRs are capable of filtering out all types of particles, including bacteria and viruses.

[ EDITOR: Again, usually “N95” or “N95 respirator” refers to a simple, tight-fitting mask that can filter very small (0.3 micron) particles. But an N95 filter can also be part of a complex mechanical “respirator”. ]

What makes [ EDITOR: simple, basic mask-like ] N95 respirators different from face masks (sometimes called a surgical mask)?

  • N95 respirators reduce the wearer’s exposure to airborne particles, from small particle aerosols to large droplets. N95 respirators are tight-fitting respirators that filter out at least 95% of particles in the air, including large and small particles.
  • Not everyone is able to wear a respirator due to medical conditions that may be made worse when breathing through a respirator. Before using a respirator or getting fit-tested, workers must have a medical evaluation to make sure that they are able to wear a respirator safely.
  • Achieving an adequate seal to the face is essential. United States regulations require that workers undergo an annual fit test and conduct a user seal check each time the respirator is used. Workers must pass a fit test to confirm a proper seal before using a respirator in the workplace.
  • When properly fitted and worn, minimal leakage occurs around edges of the respirator when the user inhales. This means almost all of the air is directed through the filter media.
  • Unlike NIOSH-approved N95s, facemasks are loose-fitting and provide only barrier protection against droplets, including large respiratory particles. No fit testing or seal check is necessary with facemasks. Most facemasks do not effectively filter small particles from the air and do not prevent leakage around the edge of the mask when the user inhales.
  • The role of facemasks is for patient source control, to prevent contamination of the surrounding area when a person coughs or sneezes.  Patients with confirmed or suspected 2019-nCoV should wear a facemask until they are isolated in a hospital or at home. The patient does not need to wear a facemask while isolated.

ORIGINAL SOURCE: Centers for Disease Control + Prevention

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