Thread by @antiviral_mktng

I drew all over this 3M Aura 9210+ with a graphite pencil and measured the resulting fit factor using a PortaCount 8020A.

There was no meaningful loss in protection. 🧵

I performed 6 normal breathing exercises wearing a 3M Aura 9210+ respirator, then spent about 45 minutes drawing a bunch of bubbles all over it.

For this experiment I wanted something easy to draw which would use up a lot of pencil graphite, simulating some ambitious art.

I used a 5B pencil because it's the softest pencil I have in the house. I also tried an HB pencil briefly, but the harder graphite makes drawing slightly more difficult. If you want to draw pencil art on a respirator, I would definitely recommend the softer pencil.

I then redonned the respirator and performed another 6 normal breathing exercises.

The result is that there is no meaningful difference between the default and modified respirator.

Here are the harmonic mean fit factors (HMFFs) for each respirator for the 6 exercises. These represent the average leakage across all of the exercises.

You will notice that the pencil adorned respirator actually performed slightly *better* than the default, out-of-package one.

This is very likely random variation. This sort of fluctuation in minute-to-minute fit factor is absolutely common when testing a respirator.

I need to note something important when interpreting results like these.

The amount of airflow through the respirator heavily influences the resulting score. If I breathe heavily, I can push my Aura score under 100. If I hold my breath for 60 seconds, I can push it over 1000.

For this reason, breathing rate is only a semi-controlled variable in PortaCount experiments, and the resulting scores should be interpreted loosely.

What we're looking for here is an obvious difference between the two test conditions. And there isn't one!

This is why I generally plot PortaCount results on a log scale. As long as two respirators test > 100 and within the same order of magnitude, they're close enough.

The same respirator could test 300 or 600 at different times, but if you get a score of 30... 😬

The individual exercise scores for the default Aura ranged from 263-373. The scores for the pencil decorated Aura ranged from 206-506.

These sound like large fluctuations but this is just normal variation. They represent differences of 0.11% and 0.28% leakage, respectively.

It's also important to note that face seal leakage dominates total leakage when wearing most respirators.

This experiment is designed to answer the question: "If I draw dope art on my respirator using a graphite pencil, am I risking my life?"

The answer to this question depends on protection *as worn*.

Fortunately the 9210+ fits my face well, so I can measure significant changes in protection due to mods.

In the present experiment, the HMFF of 6 normal breathing exercises actually *increased* from 298 to 325.

This means after 6 minutes of wear, the default Aura leaked an average of 0.33% per minute on my face, while the graphite pencil mod leaked 0.30%.

An absolute difference of a whopping 0.03%.

We aren't talking about major differences here.

So what can we conclude from this experiment?

I think it's safe for you to draw on your respirator using a pencil, as long as you don't, you know, totally cake the thing in graphite. 😆

Unlike an OSHA style fit-test, these results will generalize to your face, since the mod is not structural and I am using my own face as a control. This is a fairly pure test of whether drawing on a respirator increases inhalation resistance enough to add meaningful leakage.

I think we can be *reasonably* confident that this will generalize to pretty much every disposable respirator. Ultimately they're all based on the same technology.

But don't be reckless! If you want to draw on your respi, do a Bitrex fit-test once to verify the mod is fine.

That is, Bitrex fit-test your modded respirator one time (not every time), because I can't possibly test every respirator and mod combination. 😅

But if you can't access Bitrex for whatever reason, I don't think you're taking a significant risk with this mod.

I was surprised at how durable the Aura filtration material is, even when scribbling on it with a pencil.

But obviously, don't sharpen your pencil into a dagger-like point! Sharpen it and then draw some lines on a piece of paper to dull the point a bit, so you don't poke a hole.

Ultimately I feel accidentally poking a hole in your respirator is the most significant risk with this approach. I don't think it's a *huge* risk if you keep your pencil duller than a scalpel, but just be aware that you're technically always safest in a plain, fit-tested respi.

I will try to do additional experiments exploring the safety limits of this technique.

Happy drawing!

Oh, I forgot to report on the qualitative aspects. 😅

I couldn't perceive any additional breathing resistance, and I couldn't smell anything. I wouldn't be able to tell the difference between these two respirators in a blind test.

I thought the graphite would smudge when donning and seal checking the respirator, but it didn't!

If you have specific mods that you want tested, let me know!