Powered Air Purifier

Concept

The device's goal is to reduce exposure to aerosolized droplets by pumping clean filtered air in front of caregivers' faces when equipped with a face mask and face shield. This concept supplements existing PPE by adding a protective barrier hence reducing the risk of caregiver infection, it is not a mask replacement. The device should be worn with a N95 mask.

The goal of the device is to reduce exposure of the eyes and face to aerosolized droplets in the air that contain a viral load and to reduce the amount of CO2 between the mask and the face shield. Initial prototype testing with PM2.5 particulates has indicated a 70-80% reduction in particulate compared with the surrounding environment.


PuFFeR: Powered Filtered Flow for contamination Reduction. Pronounced "puffer"

Prototype

We completed the 5th prototype revision on April 15 2020.

The initial prototype has been tested by doctors treating COVID-19 patients at the University of Michigan hospitals.

PAPR

What is the inspiration for the PuFFeR?

The picture to the left displays a traditional PAPR which was the inspiration for the PuFFeR. The PuFFer is a miniaturized, low cost powered air filtration unit. It would operate on a similar principal, but it is not fully enclosed. Hence, the PuFFeR would not provide an equivalent completely sealed hazard free interior volume.

However, the PuFFeR has many advantages: it is less expensive (10x), easier to use (not full face, quick to put on), and much lighter (~400g vs 4500g). The PuFFeR would operate for over 15 hours on a single charge, and includes easily sourced batteries that can be quickly replaced without special tools.

Functional Description

The PuFFeR is made up of the following parts:

  1. A belt-mounted filtered blower (casing depicted to the left) that can run for 15 hours, providing 19 liters per minute of filtered air to the inside of a face shield. The power pack mounts via clip for belt or back of pants, and includes multiple belt loops on two sides to allow other fastening.

  2. A CPAP hose or other tube will run from the powered blower unit to the outlet (depicted in the first picture at the top of the page).

  3. A headpiece which clips onto a face shield frame (depicted further down in the 'clip on outlet' section).

  4. An extra visor extension which extends above the face shield and provides further protection in covering the forehead, while also decreasing the area for outside air to enter (depicted further down in the 'forehead visor extention' section).

Powered Blower

Fan specifications: 12V @ 120mA brushless DC cooling fan. We are currently using a commodity part used as 3D printer hot end cooling fans.

Fan testing: The nominal flow is 3.6 cfm without restrictions, measured as approximately 0.6 cfm (19 lpm) with the gen 2 prototype. This volume should be sufficient to displace air at a rate comparable to normal respiratory rates and at the minimum, would significantly dilutes any aerosolized droplets in the caregivers breathing space. The air flow is not so high as to dry out the eyes or chill the face- increasing caregiver tolerance to use in long shifts.

Assumptions: we assumed a typical respiration rates of 5-8 l per minute (Respiratory minute volume: https://en.wikipedia.org/wiki/Respiratory_minute_volume).

Since the PuFFeR is not a PAPR and is not intended to maintain isolation from room air, it does not need to meet the specification of commercial PAPRs (which are 115 lpm - or 4 cfm - for a tight fitting version and 170 lpm - or 6cfm - for a loose one).

Drawbacks to having too much airflow: filter life goes down; if anything manages to get past the filter, there will be more of it; the air would dry eyes, more battery power is required (increased pack weight) or reduced run time (because of higher motor power consumption).

Clip on Outlet

The clip on outlet provides low velocity flow of air directed toward the upper portion of the wearer's face. Designed to mount to Prusa RC3 style 3D printed face shields.
Clip-on modules can be quickly designed and manufactured for adapting to varying face shield models.

Forehead Visor Extension

The forehead visor extension allows coverage of the forehead and front of hair. It also reduces the gap between the face and shield to increase the effectiveness of the positive air flow.

We have 2 designs, that we are calling the ladybug and the origami. The ladybug is a design with a split center where two 'wings' fold together over the top. The origami is an unbroken single sheet using folds to provide a flat topped cap.

Both of these designs include versions where an existing Prusa RC2 or RC3 face shield can be upgraded with an upper piece of material for forehead protection (split upper/lower), or the entire visor can be replaced with a single large sheet covering the face and forehead (single full head visor).

Filter Media

A 2"x2" filter will be captured in a grooved lip between the device housing and a clip-on protective cover. The goal is that all air reaching the fan unit will have passed through the filter. The filter material is a commercially available product, and the filters will be replaced daily by the user of the device.

We are investigating different types of filtering material with different layer numbers.

3M filtrete air filters can provide substantial filtration of viral particle sizes. They are electrostatically charged filter media made of polypropylene and polyolefin plastic. This material is functionally equivalent to the material used in N95 masks. N95 masks have a formulation that is different because it must be molded and stacked for maximum capture.

MPR 2200 media are specified for a 69% filtration efficiency through a single layer. This means 69% of 300 nanometer to 1 micrometer particles are captured by a single layer. Two layers should capture 90%, three 97%, four 99%. Higher rated filters like MPR 2500 should capture 77% in a single layer of material.

An alternative filter media is CPAP filter material. An inline filter could be used to futher improve the air quality.

Because the air is drawn from behind the caregiver at waist level, the aerosol load should be further reduced as compared to near the face of the patient.

Electrical Power

The PuFFeR uses rechargeable or disposeable 8x AA's (12V @ 1900mAh) or 12v power tool battery (eg. 12V @ 3000mAh Li-ion) with fail-safe charging.On Switch: Currently uses 9V battery connector to switch on. This makes it difficult to accidentally turn off.

Recharging: The pack of 8xAA batteries are removed from the unit and charged in a standard Panasonic battery charger. Each charger holds 4 batteries and requires 3-4 hours for a full charge.

A 12V DC step up circuit is used so that air flow will stay constant as the battery voltage drops, and the blower fan continues to work even with the battery pack below 8 V. There is presently no low battery indicator LED or buzzer. The run time is in excess of 12 hours, and the current unit can accept alkaline (disposable) AA batteries in case of emergencies with a full battery pack discharge.

Tubing

The PuFFeR uses a 6 foot CPAP tubing with standard 22mm connectors. The tubing is easily sourced as medical grade consumer or healthcare equipment and easily cleaned.

Additional Opportunities

  • The PuFFeR could use a baynet adaptor N100's as filters for the powered air pack.

  • The PuFFeR could use a filtered powered air pack as air source for full face snorkel shield or half-face P100 respirator to allow respirator to fit under face shields (cartridges are too large to fit under face shields). This should also improve tolerance to use for 12 hour shifts by reducing the force needed to breath in through the filters.

dassault-systemes-simulia-sneeze-simulation-01.mp4

Aerosol Protection

© 2020 Dassault Systèmes. All rights reserved.

The simulation(s) by Dassault Systèmes and other technical or operational information represented in this video are presented as an illustration and are for informational purposes only. Any use of information presented in or derived from this video is at the viewer’s sole risk and Dassault Systèmes disclaims all related liability. Original Press Release, Open COVID-19 Group