Hack Chat Transcript, Part 2

A event log for PPE Testing Hack Chat

Breathing isn't as easy as it looks

Dan MaloneyDan Maloney 06/17/2020 at 20:050 Comments

Lex Kravitz12:41 PM
Many people started 3D printing face shields (clear plastic protector with an FDM holder). I thought that was an amazing demonstration of distributed manufacturing of 3D printing being able to produce parts that were overwhelming commercial manufacturing sources

Dmytro joined  the room.12:41 PM

Hiram12:41 PM
More than logistics, the manufacturing capacity was not enough. This was pointed out by one of the last remaining face mask manufacturers in the USA

Joseph Stavitsky12:42 PM
Yeah I'm a very late adopter and this is one of several cases where that policy bit me in the butt

Hiram12:42 PM
Face shields help, especially if someone coughs directly to someone's face, but without an airtight seal, viral particles could theoretically get through

Joseph Stavitsky12:45 PM
@Hiram what's that you say? Globalized manufacturing supply chains can't physically meet demand fast enough for emergencies? This is my shocked face

Hiram12:45 PM
Even a full face mask on someone with a beard will decrease the efficiency significantly. From all the testing it really makes you wonder what kind of protection, if any, most homemade N95 masks are providing. Probably very little

Hiram, where does your mask exhaust? Through the N95 filters or through a separate port direct to the air?

William12:47 PM
The full face snorkel masks have an exhaust port on the front, in front of the mouth. They're unfiltered.

Hiram12:48 PM
The air resistance of the filters and lack of water pressure on the mouth exhaust mushroom valve will result in most of the air exiting through the mouth and a smaller fraction through the filters. If the mouth valve was sealed, then it would all go through the filters on top of the head where the snorkel attaches

William12:48 PM
Physicians in Miami we work with have been putting surgical masks over the mouth area. It looks like a robot with a face mask on.

Lex Kravitz12:48 PM
@William haha

William12:48 PM
It's REALLY funny looking.

OK, I see it now. Yeah, I'd think moist breath going back through the filters would be a big problem

Hiram12:49 PM
I think the COVID crisis has highlighted we need more local manufacturing of PPE so we are not vulnerable to global demand, supply chain, logistics, ...

Hiram12:49 PM
The mask looks like Shrek

William12:49 PM
The photo of the face masks over the snorkel is here:

Yeah, and not just PPE. Lots of lessons to learn from all this

Bharbour12:50 PM

William12:50 PM
It's not as funny head-on as with the side view. :D

Hiram12:51 PM
I think one good thing about 3M filters is that there are many filter options that could do the job. Some have extra filtering features that are unnecessary. The ones we tested were mostly purely particulate filters

Lex Kravitz12:51 PM
@Dan Maloney Agreed - I was blown away by the 3D printed face shields that many groups around the world were making, that's the first time I've seen distributed local manufacturing happen at that scale

Hiram12:52 PM
Anesthesia developed masks mainly focused on using commercial ventilator filters, some of which worked better than others

William12:52 PM
The 3D printed face shields have been amazing, but also pretty scary.

Did you ever toy with the idea of PPAR - powered air-purifying respirators?


Powered Air Purifying Respirators (PAPR)

ClearLight™ Lens Technology Optimizes contrast and clarity in welding and light states, while providing a brighter light state to increase helmet-on time for non-welding tasks, enhancing visibility and reducing eye strain. Learn More

Read this on Millerwelds

Lex Kravitz12:52 PM
To follow up with Hiram, we also learned the limits of using different filter designs in a 3D printed design. I mentioned above that we gave up on using HEPA vacuum cleaner filters. We also found the Honeywell threaded filters weren't ideal for 3D printed adapters. Even with an SLA printer and trying several different resins we couldn't get the threading to seal well enough to pass the test. The 3M Bayonet design worked well in our hands.

Little over the top, but you get the idea

William12:53 PM
There's no quality control, and I have heard stories of them falling apart during use, which means someone ends up unprotected when they're already in a dangerous situation.

William12:53 PM
PAPR's are great, but they have a 115 to 170 liter per minute airflow, and typically weight 4.5 or so kg. They're upward of $1700 normally.

William12:54 PM
Ford + 3M have been making a $750 PAPR for this emergency (12,500 units/week, already NIOSH approved):

Lex Kravitz12:54 PM
@William yes agreed... I printed some for a group in St Louis that was collecting them for hospitals and had the same thought while taking them off my printer... is someone really going to use this???

alexwhittemore12:54 PM
@Hiram Is O2sat actually a reliable signal to detect CO2 rebreathing? If there was mixing of exhalate with inhalate, couldn't hypercapnia be a problem even despite decent O2sat?

Hiram12:55 PM
One local physician was developing a PAPR with some private money and drove to do the FDA testing. I think this was an idea they were hoping to commercialize. The first round of testing failed because the ventilator bacterial filter they used did not work. Not sure about the current status of the project. In theory it is probably easier to pass the test with a PAPR as air leaks become less of an issue


Hacked Protective Gear Keeps Doctor Safe In The Hot Zone

It's rarely a wise idea to put a plastic bag over one's head, but when the choice is between that and possibly being exposed to a dangerous virus, you do what you have to. So you might as well do it right and build a field-expedient positive pressure hood.

Read this on Hackaday

William12:56 PM
I don't think O2 sat is a good indicator of rebreathing. We measured CO2 directly in the eye chamber of the snorkel masks, and found nearly 0.5% CO2 when not using the Ocean Reef adaptor with the mushroom valve.

Hiram12:57 PM
I would have to brush on my physiology. But @alexwhittemore you may be right. Arterial blood gases would be the way to test this on a subject or the Stanford group had a way to test this in their website

William12:57 PM
Our group has been developing a solution midway between a PAPR and a face shield.

William12:57 PM
We're pursuing a new device class with FDA.

Daren Schwenke12:57 PM
@Lex Kravitz HEPA vacuum cleaner filters. We were exactly here. Good to know. Thank you.

William12:58 PM
vacuum cleaner filters are a pretty bad solution for respiratory protection.

Hiram12:59 PM
HEPA filters apparently can release carbon particles that can make the fit testing fail

Daren Schwenke12:59 PM
But they look good on paper...

William12:59 PM
They need to handle very high loads of dirt and debris before failing, and back pressure is no issue.

Lex Kravitz12:59 PM
@Daren Schwenke Yeah we liked that we could get them cheaply and easily, even at the height of the respirator filter shortages. It passed a qualitative test, but not the quantitative test. Some into on our experiences here:

Daren Schwenke12:59 PM
You have a new follower. Thank you.

William1:00 PM
They're really difficult to breathe through. NIOSH has limits on the pressure drop across filters for unpowered and powered respirators to avoid issues. Basically lungs can get hurt by pulling too hard.

Daren Schwenke1:00 PM
We also looked at the HEPA air filtration solution it looks that you ended up with, but never generated the adapter.

So here we are at the top of the hour, and I'm sure Lex and Hiram both need to get back to work. I just want to say thanks to both of them for their time today, and that we really appreciate their efforts to respond to the pandemic in a productive way. Doctors, thank you both very much!

Hiram1:01 PM
ANother thing we learned is that some 3D prints may not be airtight and an airtight coating may be necessary. We also don't know how the VOCs from the different prints could affect someone's health

Lex Kravitz1:01 PM
@Daren Schwenke I can share the 3D files if you want to try messing with them more

Daren Schwenke1:01 PM
5 solid walls, overextrude.

Daren Schwenke1:01 PM
not pretty, but airtight.

Hiram1:01 PM
Thanks to everyone! Good luck with your projects

Lex Kravitz1:02 PM
We used a coating from Smooth-On which worked well to seal up PLA prints... not always pretty but it worked

Lex Kravitz1:02 PM
Thanks all I have to get back to work as well!

Thanks Lex! Thanks Hiram!

Hiram1:02 PM
Lex and Kyle have been amazing collaborators!

William1:02 PM
That's a good call. I think that the pneumask team insisted that only resin based prints would be acceptable, but I think that didn't make sense.

Daren Schwenke1:03 PM
We were inherently lazy. :) Thank you @Lex Kravitz @Hiram . We can follow up offline if you want to share notes.

We're changing gears next week, with Walter from Gigatron:


Gigatron Hack Chat

Walter Belgers will host the Hack Chat on Wednesday, June 24, 2020 at noon Pacific Time. Time zones got you down? Here's a handy time converter! In some ways, it's good that those days are gone.

Read this on Hackaday

William1:03 PM
Thank you @Lex Kravitz & @Hiram!

Joseph Stavitsky1:03 PM
@william I think a simple solution would be a food grade silicon coating

I'll be posting a transcript shortly. Thanks all!