This is a frequently asked question, but there is no standard answer.
The simple answer:
Change the filters when the color of the filters changed to 50% grey as shown in the filter package, or
Change the filters after 2 weeks of starting using it, even if the color has not changed so much.
The long answer:
The effective duration of the filter is heavily dependant on environmental factors and usage patterns. For example:
– Where is the filter being used? Outdoors or indoors?
– Is the air pollution level very high (* footnote) when you use the filter?
– Are you using it all day long, or just during your commute?
– Are you using it for exercising, such as running or cycling, or while you are driving?
– Are you using it while handicrafting? such as wood turning?
– Is the user a big man, or a small child?
All the factors mentioned above can affect the effective duration of the filters. If you are a big guy use the filter mask outdoors for exercise, your filters will last a lot shorter than a small boy using the same filter mask mainly indoors.
Since it is not possible to give an accurate answer for the effective time duration, we instead suggest the following, for maximum protection:
1) Change the filters when they reach a 50% gray color (as shown in the filter package).
2) Maximum usage duration is 2 weeks since first use of the new pair of filters, even if they have not reached the 50% gray color.
You may ask, why 50% gray and not 40% or 60%? And why 2 weeks, not 4 weeks?
To be honest, we are also not sure! But we’ve done tests and we feel comfortable with the above recommendation, knowing that the filters are still sufficiently effective at 50% gray and after 2 weeks since first use.
Below is an experiment to find out the remaining effectiveness of a pair of filters after two weeks of use, after accumulating enough pollutant to turn it into a 50% gray.
1) Attach a pair of filters to a box fan, drawing air continuously through the filters until it changes to 50% gray (matching the picture on the filter package).
2) Insert the filter to a Totobobo mask, and ensure the watermark seal check shows the mask fits well on the user’s face.
Respirator test with 50% gray filters:
We then conduct an NIOSH standard fit test for N95 mask.
Test setup with TSI PortaCount Pro 8083 respirator fit tester
The test result is a marginal pass (Fit-factor = 100) for NIOSH N95 standard. Converting this result to filtration efficiency as following:
Filtration Efficiency = (1- 1/Fit-factor)% = (1- 1/100)% = 99%
This is not as impressive as a new pair of filters which is usually able to achieve a Fit-factor of 130+ , but it still provides sufficient protection for pollutant protection purposes.
footnote: (source: Wikipedia: Particulates)
The IARC and WHO designate airborne particulates a Group 1 carcinogen. Particulates are the deadliest form of air pollution due to their ability to penetrate deep into the lungs and blood streams unfiltered, causing permanent DNA mutations, heart attacks, and premature death. In 2013, a study involving 312,944 people in nine European countries revealed that there was no safe level of particulates and that for every increase of 10 μg/m3 in PM10, the lung cancer rate rose 22%. The smaller PM2.5 were particularly deadly, with a 36% increase in lung cancer per 10 μg/m3 as it can penetrate deeper into the lungs.