How is it possible to filter out sub-micron particles?

This question is repeatedly asked:

How is it possible for Totobobo filters to filter out sub-micron particles?

This is an important question because sub-micron particles ( eg.PM2.5 ) contained in polluted air is the major health concern. The secret of Totobobo filters is the high intensity static charges on each fiber which made up the filter matrix. When you breathe in, airborne particles follow the air and pass through the filter matrix. Fine particles are very susceptive to the static charges and therefore most of them eventually are attracted onto the filter fibers. In fact, Nelson Lab test shows Totobobo F96 filter is able to cut down 99.86% of 0.1 microns particles. Under a microscope it shows how small particles are attached to the filter fibers.

totobobo-filter-03b-800
Fig. 1  Fine particles, size range from tenths of microns down to 0.1 microns are attracted to the fibers as they pass through the complex matrix of the Totobobo filter.
totobobo-filter-02-800
Fig. 2 100X magnification view of a needle (0.6mm thickness) and filter fiber.
Totobobo filter with a needle of 0.6mm thickness
Fig. 3    Totobobo filter with a needle of 0.6mm thickness

 

Quoted from the NIOSH Science Blog below:

N95 Respirators and Surgical Masks

How do filters collect particles?

These capture, or filtration mechanisms is described as follows:

Diagram illustrating the filtration mechanisms of inertial impaction, interception, diffusion, and electrostatic attraction. In each case, fibers are shown filtering particles.

  • Inertial impaction: With this mechanism, particles having too much inertia due to size or mass cannot follow the airstream as it is diverted around a filter fiber. This mechanism is responsible for collecting larger particles.
  • Interception: As particles pass close to a filter fiber, they may be intercepted by the fiber. Again, this mechanism is responsible for collecting larger particles.
  • Diffusion: Small particles are constantly bombarded by air molecules, which cause them to deviate from the airstream and come into contact with a filter fiber. This mechanism is responsible for collecting smaller particles.
  • Electrostatic attraction: Oppositely charged particles are attracted to a charged fiber. This collection mechanism does not favor a certain particle size.

In all cases, once a particle comes into contact with a filter fiber, it is removed from the airstream and strongly held by molecular attractive forces. It is very difficult for such particles to be removed once they are collected. As seen in Figure 2, there is a particle size at which none of the “mechanical” collection mechanisms (interception, impaction, or diffusion) is particularly effective. This “most penetrating particle size” (MPPS) marks the best point at which to measure filter performance. If the filter demonstrates a high level of performance at the MPPS, then particles both smaller AND larger will be collected with even higher performance.

This is perhaps the most misunderstood aspect of filter performance and bears repeating. Filters do NOT act as sieves. One of the best tests of a filter’s performance involves measuring particle collection at its most penetrating particle size, which ensures better performance for larger and smaller particles. Further, the filter’s collection efficiency is a function of the size of the particles, and is not dependent on whether they are bio aerosols or inert particles.

Graph showing a filter's efficiency on the Y-axis and particle diameter in microns along the X-axis. Efficiency falls in the 'Diffusion and Interception Regime'.

Singapore mask designed to protects children

In the haze, young children are at greater risk because of their lungs is still under development and there is a lack of child-friendly respiratory masks. The customisable Totobobo mask offers parents a reassuring solution and is seeing strong demand from around the world.

News release
(Singapore, 4 May 2009)  As swine flu (H1N1) continues to spread, young children are at greater risk because of their lungs is still under development and there is a lack of child-friendly respiratory masks. The customisable Totobobo mask offers parents a reassuring solution and is seeing strong demand from around the world.

Totobobo mask fit children with small face size
Totobobo mask fit children of different ages

The patented Totobobo mask was created by product designer Francis Chu to meet the need for children respiratory protection. Made from “Totosoft”, a custom-blend soft plastic formulated using FDA approved sources, the mask is also equipped with two powerful electro-static filters. The mask can be trimmed to fit children as young as five-years-old. Parents can see through the transparent mask and double check if it fits their child snuggly.

For a mask to be effective, it has to fit the face snuggly, so that airborne viruses cannot seep through any gaps. Children wearing adult-sized respiratory masks, whether NIOSH-certified or not would be exposed to contaminated air due to the ill fit.

normal N95 mask does not fit children
normal N95 mask is too big for children

The National Institute for Occupational Safety and Health (NIOSH) in the USA tests and certifies respiratory devices on the market such as the current standard N95 masks. This test is only conducted on adults. The certification determines the filtration efficiency and does not guarantee how well the masks fit. All NIOSH-certified respiratory masks, such as N95 masks, are fixed sizes and do not come in smaller sizes for children.

In 2003, when SARS (Severe Acute Respiratory Syndrome) first broke out, Francis Chu, a father of two, got first-hand experience of the anxiety of parents concerned about his children’s safety. His children were only six and eight-years-old. At that time and he could not find a mask that would fit their small faces.

“I felt hopeless knowing that my children were in imminent danger if they go into crowded public space like schools or playgrounds and that I could not do anything about it.”
“The sense of threat prompt me into looking for a design solution that will fit all face shapes including children.” explains Francis.

The customisable Totobobo respiratory mask that Francis eventually created, after experimenting with hundreds of prototypes, fits both adult and child. Its soft and light material (only 20grams) makes it less irritable for children who might find it uncomfortable wearing a normal mask.

“I was thinking from a parent’s perspective during the design process and that pushed me harder to make the mask as practical as possible. I am happy to know that with the child-friendly Totobobo mask, parents now have a practical choice to better assured of their children’s safety,” adds Francis.

Related:
Time for a better mask to protect children
Parent testimonial

TOTOBOBO mask in NIOSH site

Totobobo mask was spotted in NIOSH NO-FIT-TEST workshop page Totobobo mask was spotted in NIOSH NO-FIT-TEST workshop page

I was surpriced when my friend show me this page in CDC site. NIOSH, the National Institute of Occupational Safety and Health under CDC, is the US organization who certify the well known N95 mask. What made TOTOBOBO, a little known Singapore invention of respirator mask, appears in this heavy weight website?

No, TOTOBOBO is not certified by NIOSH, at least not yet. The picture of an early version of TOTOBOBO mask found in the NIOSH website is to serve as an inspirational example for a“No Fit Test” filtering facepiece respirator workshop.The workshop will be conducted in Nov. 6 later this year and the objective is:

“To better understand the interdisciplinary research needs and challenges in developing and certifying a universal “no-fit-test” filtering-facepiece respirator”

I think this istotallyappropriate and it shows NIOSH recgonize the need to improve the current procedure in order to motivate manufacturers to innovate toward the direction of “No fit test” respirator.

Why is this big fuss about “No fit Test”?

If you read carefully the fine text of your respirator instruction, you will notice a statement similar to this:

“Before use of this respirator, a written respiratory protection program must be implemented meeting all the requirements of OSHA 29 CFR 1910,134 such as training,fit testing, medical evaluation, and applicable OSHA substance specific standards.”

The simple fact is, the rated protection value will be drastically reduced if the mask does not fit your face, and there is no other ways to tell except by doing a fit-test. Buying a mask is easy, but getting a mask fit-tested on each individual is a challenge. In emergency situation like flupandemic or haze outbreak, it is simply not possible to get everyone a fit tested at once.

One can start to sense the “pain of fit test” and how touchy this issue is from the following comment in one of theNIOSHscience blog:

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NIOSH debate how often to fit test
NIOSH debate how often to fit tes

Hopeful to see Fit-Test to be lifted– Edward Hernandez, City of Hialeah, Fire Rescuesays:- Thank you for proposing a study as this. For a while now this OSHA (Fit-test)requirement has been a burden to our Fire/EMS service.

Hopeful to see Fit Test to be simplified-Peggie Reinhardt, RN BSN,says:

I would be interested in this study, we currently fit test our employees annually. If this process could be shortened or redesigned so that it was easier to do would help tremendously.

Fighting to keep Fit-Test in organization– Sgt. Julie Lovesays:

I would be interested in being part of this study on the law enforcement side. We fit test our officers annually but many departments do not. Law Enforcment traditionally has fallen down in this area as many agencies just give their officers their masks without any fit testing. We also fight the battle with our management with what is mandated.

Worry that No-Fit-Test= Not Safe-Kevin MacDonaldsays:

I am concerned that changing the fit test frequency while cost effective may defeat its overall purpose.when fit testing went from every 6 months to one year as a requirement of OSHA it was a step back.

Confused andconcern-Kelly Russellsays:

I am glad this study is being done. Respiratory fit testing is expensive for employers and it will be good to have a current answer when asked why we have to do the testing so often….or maybe not so often as the case may be.

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No matter what, the setting up of this workshop itself is already a breakthrough, and we are definitively happy to be associate with the solution side of the problem. We hope the result of the workshop will bring more practical innovation into the design and certification of respirator, especially taking people like housewife and children who don’t have access to fit-test equipment but also deserved to have good protection when situation come.

Clearly a Better Way to Check for Safety

The protective function of a respirator mask is based on two functions;
(1) the filter media must let in air but stop harmful and unwanted particles from entering the breathing zone.
(2) the mask must fit the users face and form a complete seal so that no air bypasses the filter media and enters the breathing zone directly.

Filter + Face seal = good protection

principle of respiratory mask protection

Modern technology has produced highly efficient filter media that can achieve up to an incredible 99.9% filtration efficiency. Ensuring a secure mask-to-face fit, however, is not nearly as simple. Rarely do users achieve a professional-grade fit, and they are surprised when they do.

Fit-testing is a task that requires a trained professional, special equipment, knowledge and skills, and considerable time. There is QUALITATIVE fit test based on subjective senses of the user, and there is QUANTITATIVE fit test based on objective measurement which compares the particle counts inside and outside of a mask. The National Institute of Occupational Safety and Health (NIOSH) recommends that such a fit-test be conducted yearly for each user so as to ensure proper usage. Fit testing can determine if a mask fits the user during the test, but can not tell for sure if the mask still fits the user days or months afterwards. These fit-testing procedures are limited to occupational users and not commonly available. The general public has neither the equipment, nor training, nor expertise, nor regular access to professionals who do in order to conduct professional-grade testing on their protective respiratory masks when they need it.

In a recent study Respiratory Donning in Post-Hurricane New Orleans (published on the US CDCwebsite in May 2007), researchers found 76% participants were not able to demonstrate proper donning, resulting in the compromising of their protection. This study group should know a thing or two about proper protective mask use considering the ordeal they went through during the post-Katrina clean-up of New Orleans. Imagine in an emergency situation, what would happen if the public needed to wear respirators to protect themselves? How many of these people will be able to fit their mask properly? Less than 24%, perhaps? CDC has been reluctant to recommend N95 masks for the public use because for 3 out of 4 people the poorly fitted respirator may provide a fault sense of security and encourage risky behavior.
The Prince of Wales Hospital of Hong Kong conducted a study where subjects who had previously passed a fit test were asked to properly don a N95 mask and then check for adequate sealing. These same subjects were then given a TOTOBOBO mask which they have not previous experience and conducted the same test. The results found that although the TOTOBOBO mask performed slightly less than the N95 mask, most test subjects did achieve the appropriate fit and pass the test. How did the non-fit tested Totobobo match the fit-tested N95 mask for this group of users?

Transparent surface indicates good face seal of Totobobo mask
Transparent surface indicates good face seal of Totobobo mask

The TOTOBOBO mask solves the uncertainty about proper fit in a simple but extremely effective way. The transparent mask makes fit checking an easy task. Check around the perimeter of the mask and you can immediately decide if the face seal is good or not. This simplicity, combined with a soft material that comfortably fits your face, makes fitting a lot more intuitive and reliable. Now you can perform a more reliable face-fit check every time before entering a contaminated area. This is certainly more reassuring than relying on once a year fit test.

Reference:
ESICM Annual Congress-Totobobo-mask-1044