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KN95 Mask
A non medical KN95 mask is a half face, filtering facepiece respirator that has met the Chinese GB2626-2006 performance standards for these devices. The demand for KN95 masks in North America has increased significantly in the past year due to the spread of Covid-19.
Performance Standards For KN95 Masks
GB2626-2006 standards are broadly equivalent to those set for N95 masks by the U.S. National Institute For Occupational Safety & Health (NIOSH) in the United States. Broadly, they require non medical KN95 Masks to achieve the following:
- A filtration rate of at least 95 percent of NaCl sized particles. Specifically, KN95 masks are required to filter at least 95% of non oil particles with size 0.3 microns or more;
- Inhalation resistance of not more than 350 Pa and exhalation resistance of not more than 250 Pa. The flow rate of particles used in this assessment should be 85 L/min.
- In addition to the above standards, GB2626-2006 standards require KN95 Masks to “be a tight fitting with face, and be free from deformation during the service life”.
- A KN95 mask is also required to demonstrate a proper fit. To do this, it must meet minimum performance standards where TIL (Total Inward Leakage) is required. Total Inward Leakage refers to the amount of contaminated air leaking through the seal between the wearer’s face and the edges of the respirator. This is consistent with the requirement mentioned above that the KN95 masks should be “tight fitting with face”.
Other Requirements
There are also labelling requirements – a non medical KN95 mask should bear the number and year of publication of the standard to which it is subject. It should also bear the type and grade of the filter elements (e.g. “KN95 ” in this case).
One significant difference between the standards governing KN95 and N95 masks relates to the harnessing mechanisms that each must use. In general, N95 masks use a head strap harnessing mechanism. Studies by the NIOSH have reported that the use of ear loops makes it more difficult to achieve the air tight fit required of these devices.
On the other hand, most KN95 masks (whether medical or non medical) use ear loops (athough this is not a specific requirement). There are some exceptions to this rule – for example, the DynaPro KN95 Respirator uses headstraps.
Medical vs. Non Medical KN95 Masks
As with N95 masks, KN95s fall into two categories – medical and industrial. Medical KN95s are actually governed by slightly different standards known as GB19083-2010. They are intended for use in healthcare settings in which the user may be exposed to blood spray or other potentially hazardous liquids.
The main difference between the GB2626-2006 (non medical) and GB19083-2010 (medical) standards are:
- Medical KN95s are required to conform to synthetic blood resistance standards. Specifically, these masks must be able to prevent the penetration of 2mL of synthetic blood (sprayed onto the mask at 10.7 kPa) from penetrating to the inner surface of the mask;
- Medical KN95s must also conform to “surface wetting resistance” standards;
- The medical versions of KN95s must also demonstrate less than stipulated maximum amounts of bacterial, fungal and other harmful substances on the surface of the mask.
In addition to the above, medical KN95s are not subject to the TIL requirements that apply to non medical masks. Instead, a medical KN95 must demonstrate a “fit factor” that is not less than 100.
Finally, medical KN95s are not subject to the labeling requirements we have described above for their non medical equivalents.
Exhalation Valves
A KN95 mask with an exhalation valve is subject to leakage performance requirements in respect of the valve. These are:
- Depressurization to 0 Pa >= 20 seconds;
- Force applied to be -1180 Pa; and
- CO2 clearance to be less than or equal to %.
However, the KN95 masks in this section do not have exhalation valves, so these standards do not apply to them.
How Do KN95 Masks Work?
As with N95 masks, each KN95 depends for its filtration performance on one or more layers of melt blown fabric. The fabric is essentially a mesh of synthetic polymer fibres – technically known as a nonwoven polypropylene fabric. This fabric is produced using a melt blowing manufacturing process.
The key property of the melt blown fabric layer is its ability to retain an electrostatic charge that attracts potentially harmful particles and prevents them penetrating the mask. To understand how this works, think of the way lint particles stick to articles of clothing when you remove them from a dryer.
Limitations
As we have mentioned above, KN95 masks do not provide protection against oily particles, even when these are larger than 0.3 microns. This means that they should not be used when elements such as lubricants, glycerine or cutting fluids are expected to be present.
The masks should also not be used in situations in which the user expects to encounter vapors or other substances that may pose a hazard to the eyes. In those situations, a full face respirator that protects the eyes should be chosen instead.
KN95 masks also depend on a supply of air being present. If the user expects to encounter a situation with less than adequate amounts of oxygen (e.g. during fire fighting activity), a KN95 mask will not be a safe choice. Instead, it is better to use an apparatus that will provide an independent source of oxygen.
Finally, KN95 masks are not designed to be effective in the presence of hazardous gases or other vapors. In those situations, a cartridge respirator is a preferable choice. This type of respirator is equipped with a cartridge to filter the hazardous vapors out of the air that is then breathed by the user.
How Do These Masks Compare To Other Facial Protection Devices?
Having explained how KN95 masks compare to N95 masks, we will now briefly explain how they compare to the two other devices commonly used for protection from COVID-19 infection. These are disposable face masks and face shields.
Comparison With Disposable Face Masks
Both KN95 masks and medical disposable face masks are half face devices. They protect the nose and mouth from possible infiltration of harmful particles (including viral and bacterial particles). However, they do not protect the third location of facial mucous membranes – the eyes – from bacterial or viral infiltration.
KN95 masks and disposable face masks differ in that the former provides an airtight seal of the mouth and nose while the latter do not.
Both types of mask have limited reusability and cannot be washed and reused.
In addition, disposable face masks have lower filtration efficiencies than KN95 masks. Most KN95 masks have two layers of melt blown fabric while disposable face masks generally have only one layer. As a result, disposable face masks generally have filtration rates between 80% and 90% compared to the 95% and higher filtration rates from KN95 masks that meet the GB2626-2006 standard.
Comparison With Face Shields
Probably the most important difference between KN95 masks and face shields lies in the fact that face shields protect all 3 facial mucous membranes – i.e. eyes, nose and mouth. As a half face respirator, KN95 masks protect only the nose and mouth.
Face shields are also reusable, provided they are properly handled and washed. As mentioned above, KN95 masks cannot be reused indefintely. In fact, when used in an environment in which there is a high risk of exposure to viral infection, KN95s should not be reused at all.
However, face shields do not provide an air tight seal against potential hazards. KN95s, on the other hand must provide such a seal to be compliant with the GB2626-2006 regulations.