We are now almost a year into the surging coronavirus epidemic. There has been increasing demand for PPE to properly protect healthcare workers and others from the risk of infection. Traditionally, N95 respirators have been the standard in North America where particulate filtering facepiece respirators are concerned. However, KN95 respirators have recently appeared as an alternative. It is therefore natural to compare N95 to KN95 respirators to understand their relative strengths and weaknesses. In this post, we compare N95 vs KN95 respirators and attempt to answer the question: KN95 vs N95 – which is better and in which circumstances?
N95 really refers to the performance standards applied to particulate facepiece respirators in North America, while KN95 refers to the standards applied to the same respirators when manufactured in China. We shall perform the comparison by comparing the performance levels in each area that define each of these standards to understand whether either standard is more or less rigorous in a particular area.
Both N95 and KN95 respirators have commercial and medical subcategories, with the performance standards applicable to medical subcategories being somewhat more rigorous in each case. In general , medical KN95s and N95s must also demonstrate resistance to blood penetration as well as microbiological particles. Medical KN95s must also demonstrate low or non detectable levels of various types of bacteria while no such requirement applies to medical N95 respirators.
The comparison below focuses on commercial KN95 vs N95 relative performance.
Filtration Levels – N95 vs KN95
Both N95 and KN95 respirators are required to block at least 95% of non oil particles of size around 0.3 microns or more. As a reference, a micron is around 1/1000th of a millimeter.
Therefore, as far as this particular performance standard is concerned, the N95 vs KN95 comparison does not produce any differences in performance.
Tests of filtration performance are normally performed using sodium chloride (NACl or salt) particles. The air flow rate used to measure filtration is 85 L/min.
This is one area in which there is a significant difference between the two standards. N95 respirators almost universally use headstraps that go around the back of the head. Earloop harnessing, in which the straps go around the ears, are extremely uncommon. In fact, recent NIOSH testing has uncovered evidence that earloop harnesses can provide a less than satisfactory fit to the facial contours. This in turn can cause air and harmful particulate matter to leak through the seal between the respirator and the skin. Each N95 headstrap must be capable of absorbing up to 2.2kg of force.
KN95 respirators on the other hand generally use the earloop mechanism. Some KN95 designs, such as that of the DynaPro KN95 respirator, use headstraps instead of earloops in order to address this potential problem. This design choice will generally eliminate any N95 vs KN95 performance differences where the harnessing mechanism is concerned.
Another important performance metric applicable to particulate facepiece respirators is that of inhalation/exhalation resistance. The idea is that, while the respirator should block salt sized particles, it should present the least possible resistance to air molecules. This ensures that the wearer can easily get as much oxygen as he or she may need while wearing the device.
Inhalation/exhalation resistance is normally evaluated by measuring the difference in air pressure difference on the two surfaces of the respirator. The lower the inhalation resistance, the lower the pressure differential. This is so since air will more easily flow through the respirator material to eliminate pressure differences.
There is no N95 vs. KN95 difference where this metric is concerned. Both standards mandate a maximum pressure difference of 343 Pa. for inhalation and 245 Pa for exhalation. Under both standards, testers must use an air flow rate of 85 L/min for this measurement.
Total Inward Leakage (TIL) – N95 vs KN95
Total Inward Leakage measures the ability of a respirator to restrict the inward leakage of contaminated air under various circumstances. A facepiece may meet the 95% filtration criterion mentioned above, However, its performance is still dependent on its ability to block harmful particles from leaking through the interface between its edges and the wearer’s skin. This performance aspect is what the TIL aims to measure.
The TIL% measures the % of contaminated air inside the respirator. This is done by starting with pure uncontaminated air. Testees then subject the respirator to several different “actions” such as putting on or off, twisting, adjusting, etc. Testers then measure the contaminated air % in the respirator after the testee has completed performing the “action”.
The KN95 respirator TIL standards are based on 10 testees each performing 5 “actions” on a respirator (50 in total) and require:
- that the TIL % resulting from at least 46 out of the 50 actions should be under 11%;
- that at least 8 out of the 10 testees should have a total TIL% less than 8%.
Unlike KN95 respirators, N95 respirators do not have specific TIL% requirements. Instead, they are subject to a general requirement that they should be capable of fitting persons with various facial shapes and sizes. This is achievable by offering varying facepiece sizes or offering a single “one size fits most” facepiece.
N95 vs KN95 – Conclusion
Based on the above information, we can conclude that there are 2 areas in which the performance of these 2 designs can potentially diverge:
- The more common use of the headstrap among N95 designs, which generally favours the N95 design. However, as mentioned above, some KN95 respirators use headstraps and that will eliminate this difference;
- The more specific TIL % measurement criteria applicable to the KN95 design vs. the more general and subjective fitting criteria applicable to the N95 respirator.
In all other areas, the performance standards of N95 and KN95 respirators are fundamentally equivalent.