Modular Versatile Powered Air-Purifying Respirator PAPR

DisclaimerandProjectGoals:

The goals of this project are to share and encourage the development of an open-source PAPR design that differs and may have certain advantages compared to existing designs. I discourage the creation of such a device for personal or work use in its current form. Hopefully, future designs can undergo testing protocol such as that underlined in the following article of one existing design :

Pressure Optimized PowEred Respirator (PROPER): A miniaturized wearable cleanroom and biosafety system for aerially transmitted viral infections such as COVID-19 - ScienceDirect

Abstract: Here is presented a powered air-purifying respirator (PAPR)design for continency scenarios which could potentially be more versatile when compared to existing 3D printed open-source designs. The current SARS-CoV2 pandemic highlighted how inadequate national personal protective equipment reserves were both in the United States and around the world. Efforts to solve this problem have included the use of 3D printed mask designs, and positive airway pressure respirators. One challenge with existing PAPR designs is their lack of flexibility when accommodating differing filter as well as machine blower sizes. This design outlines a simple soft flexibility body that requires less 3d printing to accommodate filters, blowers of all sizes, and even the incorporation of existing N95 respirators. This device could benefit from continued design work and testing.

Background

The current SARS-CoV2 pandemic highlighted how inadequate national personal protective equipment reserves were both in the United States and around the world. However, even during the 2009 H1N1 pandemic which was much smaller in scale, N95 respirators in some systems in North America were depleted suggesting that personal protective equipment supplies may be more vulnerable than initially thought (Rebmann et al 2009; Murray et al 2010). Such shortages can not only be attributed to increased demand, but during the SARSCov2 pandemic, production which relied on global supply chain, manufacturing and logistics were disrupted (Ranney et al 2020). Together, this had dire consequences such that many of the infections and deaths in healthcare workers across the globe could at least be partly attributed to inadequate supplies of necessary personal protective equipment. Such shortages and desperation led even the United States to, during the April 2020 NYC outbreaks, issue guidance from the CDC suggesting the use of scarves or bandanas when supplies of masks and respirators were low. Such guidance was in addition to emergency policies okaying mask reuse, extended use, and reprocessing.

However, given the intended single use design of n95 respirators, there have been problems with reuse, extended use and reprocessing. Previous literature suggests that with repeated N95 mask “donning and doffing”, there is a decline in fit and performance of masks such that 5 consecutive donnings can be performed before fits are unsatisfactory (Bergman et al 2012). Degradation of fit can be attributed to both technique but also attributed to degradation of elastic bands, and breakage of nose clips (Vuma et al 2020, CDC 2020). In addition to concerns with proper fit, reuse of N95 respirators requires reprocessing and decontamination. FDA emergency use authorization has led to decontamination and reprocessing methods such as UV irradiation, ionized hydroperoxide and moist heat. Such methods can possibly further damage elastic band required for fit (Czubryt et al, 2020). Beyond the time and expense of retesting for fit, the cost of reprocessing is also expensive atup to 6 times the original unit cost of the mask (Dugdale et al 2020).

To address these concerns multiple projects have leveraged 3D printing to create both masks and even powered air purifying respirators. These open-source designs, while often without certification, are freely sharable for others to download and manufacture. Some concerns with some of these current 3d printed PAPRs include difficulties securing an adequate supply of components such as filters, and blowers (Mcavoy et al 2020). Problems with 3D printed masks include achieving the proper fit for a wide variety of different faces (Mcavoy et al 2020). To overcome these difficulties, one research group set out to improve upon the current supply of facial masks by 3D printing frames to accompany existing N95 masks to improve durability of fit. While successful in securing fit in instances where fragile straps were not utilized, the frames could not improve fit in those who previously did not pass baseline fit testing (Mcavoy et al2020). We believe there exists an in between opportunity to design a more versatile low cost PAPR device that can use both existing N95/KN95 masks or other industrial filters, while maintaining the comfort and fit advantages of a PAPR.

Versatility in the design of our Fan/Filter unit means the ability to accept multiple filter sizes, and centrifugal fan sizes. The advantage of this versatility is increased supply of acceptable components in situations of difficult supply chain like a pandemic. Centrifugal fans of differing dimensions could be used if meeting other technical standards. Filters accepted could range from industrial HEPA filters to N95 and even some KN95 respirators are authorized for emergency use. Beyond existing supplies, another advantage of utilizing existing KN95/N95 masks in a fan filter unit with a separate more durable facial interface is by separating the filter from the facial interface, there is effectively no “donning and doffing” and thus no compromise in fit or need for costly reprocessing. One fan filter unit could also possibly be shared by multiple team members who each connect their own individual facial interface when needed, thus possibly increasing cost effectiveness.

In this project we outline the design of a more versatile soft body positive airway pressure filter fan unit. This design contrasts with existing open-source projects that utilize a 3d printed exterior shell to fit a specific fan and or filter. We hope that the greater community of makers as well as individuals in industry and healthcare agree with the above highlighted advantages and improves upon the current design to ultimately make and disseminate something impactful.

Hardware Description

The PAPR body consists of a flexible outer plastic film body (Figure 3). Filters and blowers fix to the flexible plastic body via hose clamps. Circular, and other shaped filters have the benefit of direct fixation, while existing facial respirators and or other filter materials will require an additional 3D printed adapterto clamp to the flexible body (Figure 4, 5). The PAPR body would connect to a standard facial interface or hood.

Advantages of this design compared to existing open source PAPRS

1. Flexible exterior plastic body (Figure 3)

• can accommodate a larger variation of filters and centrifugal fans of differing dimensions without needing to redesign new 3d printed exterior for a different set of components.
• minimize the amount of 3D printing when compared to a solid 3d printed exterior as only internal adapters for clamping may need to be printed
• allows for some degree of visualization of integrity of positive pressure system through distention of the plastic body
• allows for visualization of all components in case of troubleshooting

2. Hose clamp fixation

• Easy assembly and disassembly.
• Allows for air seal

The rest of the hardware components consist of plastic vinyl bag, flexible hosing, house clamps, snorkeling mask with one-way valves, Arduino microcontroller, Arduino Motor Shield, 12V centrifugal fan, 12V external Lithium-Ion battery supply, 9V battery.

Future Considerations/To dos

1. Exploration of different flexible plastic materials.

• this project used a clear plastic vinyl bag that had the disadvantage of stiffness that led to cracks when trying to conform to smaller dimensions.
• Ideally would find material that balances, strength and flexibility and has the ability to be formed easily into a tube via folding over on one aspect and welding the plastic together

2. 3D Print Adapter to fit N95/KN95 mask (Figure 6)

• ideally would good fit and sealing of n95/kn95 mask to the flexible hosing that attaches to facial interface.
• Adapter would have one area of increased structural integrity such that a hose clamp could be affixed exteriorly to attach the adapter mask to the exterior soft body as well as the flexible hosing.

3. Internal Pressure Sensor

• Distal to the fan filter unit, the system need not be airsealed, but should have sufficient positive pressure such that no external organisms can enter. A pressure sensor distal to the filter may help objectify this
• +/- potentiometer to adjust force of the centrifugal fan and positive pressure generated.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

References

2020. Implementing Filtering Facepiece Respirator (FFR) Reuse, Including Reuse after Decontamination, When There Are Known Shortages of N95 Respirators [Online]. Centers for Disease Control and Prevention. Available: https://www.cdc.gov/coronavirus/2019-ncov/hcp/ppe-strategy/decontamination-reuse-respirators.html [Accessed].

BERGMAN, M. S., VISCUSI, D. J., ZHUANG, Z., PALMIERO, A. J., POWELL, J. B. & SHAFFER, R. E. 2012. Impact of multiple consecutive donnings on filtering facepiece respirator fit. Am J Infect Control, 40, 375-80.

CZUBRYT, M. P., STECY, T., POPKE, E., AITKEN, R., JABUSCH, K., POUND, R., LAWES, P., RAMJIAWAN, B. & PIERCE, G. N. 2020. N95 mask reuse in a major urban hospital: COVID-19 response process and procedure. J Hosp Infect, 106, 277-282.

DUGDALE, C. M. & WALENSKY, R. P. 2020. Filtration Efficiency, Effectiveness, and Availability of N95 Face Masks for COVID-19 Prevention. JAMA Intern Med.

MCAVOY, M., BUI, A. N., HANSEN, C., PLANA, D., SAID, J. T., YU, Z., YANG, H., FREAKE, J., VAN, C., KRIKORIAN, D., CRAMER, A., SMITH, L., JIANG, L., LEE, K. J., LI, S. J., BELLER, B., SHORT, M., YU, S. H., MOSTAGHIMI, A., SORGER, P. K. & LEBOEUF, N. R. 2020. 3D Printed frames to enable reuse and improve the fit of N95 and KN95 respirators. medRxiv.

MURRAY, M., GRANT, J., BRYCE, E., CHILTON, P. & FORRESTER, L. 2010. Facial protective equipment, personnel, and pandemics: impact of the pandemic (H1N1) 2009 virus on personnel and use of facial protective equipment. infection control and hospital epidemiology, 31, 1011.

RANNEY, M. L., GRIFFETH, V. & JHA, A. K. 2020. Critical Supply Shortages - The Need for Ventilators and Personal Protective Equipment during the Covid-19 Pandemic. N Engl J Med, 382, e41.

REBMANN, T. & WAGNER, W. 2009. Infection preventionists' experience during the first months of the 2009 novel H1N1 influenza A pandemic. American Journal of Infection Control, 37, e5-e16.

VUMA, C. D., MANGANYI, J., WILSON, K. & REES, D. 2019. The Effect on Fit of Multiple Consecutive Donning and Doffing of N95 Filtering Facepiece Respirators. Ann Work Expo Health, 63, 930-936.