osPAPR | Development of an open source PAPRs unit
Virtually Maker Faire 2020
May 22nd-23rd
The Hack The Pandemic team focused on designing an alternative to current PAPR units. Specifically, we concentrated our efforts to design a unit that could replace the pump unit (air pump, battery, filter, and electronics controller). A hood redesign is not needed as these are still readily available. We understand that many hospitals and countries around the world face challenges in paying for the expensive PAPR units. To solve this, we made sure that all of our decisions were made with economy and reproducibility at home in mind. All components in our design can be easily found or produced by the average person to allow for crowdsourcing of more units.
Our electronics design consists of a printed circuit board with a Pro Trinket Microcontroller, a pressure sensor, and a temperature sensor. The Pro Trinket is able to monitor airflow through the pressure sensor and adjust fan speed accordingly. If the airflow still remains low, it alerts the user of low airflow, both through the use of audible and visual alerts. It also has a temperature sensor that allows the device to automatically shut off if the temperature exceeds the safe operating temperature range, allowing for safe usage of the device. The user is alerted if the device overheats through an audible alert as well. In addition, a filter life indicator of 5 LEDs signifies when it must be replaced. After replacing the filter, the user presses a button to reset the filter indicator. The custom PCB is the most difficult part to manufacture, requiring a PCB production house such as OshPark to produce the component in small batches. Those who wish to make the project are able to download the CAD and CAM for the PCB from our Github Page and upload them to OshPark for production. Boards arrive within 72 hours of ordering to be fitted to their components. We will be providing easy kits containing the PCB and subsequent electronics to anyone who is producing the osPAPR.
The osPAPR utilizes a 120mm computer fan in a parallel configuration to the case. Air is drawn in from the section of the case closer to the user’s back and pulled through a set of MERV 13 furnace filters before being sent through the tube to the hood of the PAPR. We chose to utilize the MERV furnace filter due to the fact that a MERV 13 and a N95 mask have equivalent success rates of being able to be able to block more than 95% of 0.3 micron particles from passing through the filter substrate. In accordance with the NIH approved specifications for MERV filters as N95 replacements, 5 layers of MERV fabric are sandwiched between two layers of cotton and stretched tight under the fan. The case is divided into two compartments: a ‘hot’ compartment houses the filter and fan, and a ‘cold’ compartment houses the electronics and battery. This allows for easy disinfection and cleaning as only half of the case has been exposed to potentially contaminated air.
Ease of manufacturing was a key design element we had to work around when working on our project. In order to make the largest impact, the case of osPAPR has been designed to be almost entirely 3D printed. This allows large print farms to produce the osPAPR in bulk. Individuals can then assemble sections such as the electronics or filter that can be quickly combined and delivered to medical workers.
This design optimises low costs and is designed to be available to any hospital. In addition, osPAPR is smaller than other PAPR devices while still maintaining ~10 hours of battery life and containing all of the same visual and audible safety measures. At the time of writing, the cheapest 3M equivalent costs $908 USD. A major keystone of our design was our drive to release the osPAPR as a DIY kit that could be produced cheaply and easily by makers and engineers at home using only a 3D printer and a soldering iron with readily available components. This will allow us to scale production of the osPAPR through our network of makers to ensure that production is able to keep up with demand across the east coast.
