key: cord-0971382-6n2m0gg4
authors: Kessel, Jeff; Saevig, Christopher S.; Hill, W. Cary; Kessel, Benjamin; Hull, Matthew S.
title: An Emergency Powered Air-Purifying Respirator From Local Materials and its Efficacy Against Aerosolized Nanoparticles
date: 2022-03-27
journal: Inquiry
DOI: 10.1177/00469580221087837
sha: a9563b5f3140ff32dc0a3c8301d965114c704483
doc_id: 971382
cord_uid: 6n2m0gg4

We describe an approach used by a rural healthcare provider to convert surgical helmets into emergency powered air-purifying respirators (PAPRs) at the onset of the COVID-19 pandemic. The approach uses common materials and efficacy was demonstrated against aerosols measuring 7 nm to 25 μm in diameter.

During the COVID-19 pandemic, shortages in personal protective equipment (PPE) were especially severe in resource-constrained areas. 1 Overcoming such shortages, particularly in healthcare and public safety settings, became an urgent global priority. In the United States, the National Institute for Occupational Safety and Health (NIOSH) published an interim final rule establishing a new class of powered air-purifying respirators (PAPR) that aimed, in part, to help alleviate strains on respirator supplies. 2 Healthcare professionals in rural Virginia sought to alleviate such shortages by converting surgical helmets into emergency powered air-purifying respirators (PAPRs). Similar efforts have been reported 3, 4 but efficacy against sub-micron particles associated with airborne transmission of SARS-CoV-2 5 is largely unknown. We demonstrated an approach for converting surgical helmets into emergency-use PAPRs with readily available materials and verified its efficacy against nanoscale aerosols using an improvised PAPR evaluation method. The PAPR was originally intended for non-sterile use. Practical modifications to the donning and doffing procedure could theoretically allow for sterile use but were beyond the scope of the present work. While makeshift solutions present numerous risks and are never recommended by authorities such as the US Centers for Disease Control and Prevention (CDC), the PPE shortages and supply chain disruptions encountered during the early phase of the COVID-19 pandemic, prior to the issuance of NIOSH's interim final rule for PAPRs 2 , presented healthcare providers with especially dire choices and no viable alternatives.

The emergency PAPR is achieved by adding supplemental filter media over the air intake of a surgical helmet and then compressing the media into the groove of a machined polyvinyl chloride (PVC) ring mounted to the underlying surgical helmet. Assuming that most healthcare settings already have access to surgical helmets and sterile wrapping, the remaining materials (i.e., PVC pipe and cable ties) can be acquired from a local hardware store for less than $30 USD (excluding ring machining costs, which will be locally variable) and used to modify a dozen or more surgical helmets. Assembly consists of the following four steps ( Figure 1A ) which are demonstrated in an online video 6 4. Add/secure supplemental filter media: Place a 24" x 24" piece of filter media, externally, over the toga/ helmet air intake and secure it to the internal helmetmounted PVC ring using a 48" cable tie to compress the filter/fabric layers into the machined groove (use a tensioning tool to securely tighten the cable tie).

Methods for evaluating the performance of PAPRs are limited, 7 so we devised an improvised procedure. We used the ring-mounted surgical helmet to outfit two types of supplemental filter media plus a negative control onto an instrumented test manikin. Filter media included sterilized surgical wrap (Halyard H600, Owens & Minor Global Products, Mechanicsville, VA) and vacuum HEPA media (ShopVac ® , Williamsport, PA). We then evaluated the filtration efficiency of each media type against two aerosol challenges: 1) a sodium chloride (NaCl) aerosol generated using a Particle Generator Model 8026 (TSI, Shoreview, MN) and 2) a silicon dioxide (SiO 2 ) nanoaerosol generated as described by Ostraat et al. 8 and applied to PPE evaluation as described by Hill et al. 9 The size distribution and concentration of each aerosol challenge was monitored outside and inside the experimental PAPR in triplicate one-minute averaged samples using a TSI NanoScan Model 3910 Scanning Mobility Particle Sizer and a TSI AeroTrak Model 9306. Additionally, a TSI Model 8030 Portacount Pro Respirator Fit Tester was used to collect tandem measurements both inside and outside of the PAPR. 10 The effect of filter media on airflow through the helmet was evaluated using a Model ABM-200 Wireless Airflow and Environmental Meter (CPS Products, Inc., Miramar, FL) mounted to the helmet's exhaust. The test apparatus was assembled and all challenges performed within a cleanroom to reduce background particles to <10 particles cm -3 ( Figure 1B) . Carbon dioxide (CO 2 ) within the breathing zone of a volunteer wearing the PAPR and walking on a treadmill was measured using an ExplorIR ® -W 20% CO 2 Sensor (CO2Meter.com, Ormond Beach, FL) for the negative control and the 2x H600 treatment, as these test conditions were expected to have the least and greatest impact, respectively, on airflow resistance and CO 2 levels.

Average (±SD) geometric mean size distributions and concentrations for the aerosol challenges were 52±1.8 nm and 7,100 (±1,040) particles cm À3 for the NaCl challenge and 35 ± 1.9 nm and 87,000 ± 14,000 particles cm À3 for the SiO 2 nanoaerosol (Table 1) . Without modification, the surgical toga removed >60% of the challenge aerosol fraction measuring 0.3-25 μm; filtration efficiency was especially poor for For clarity, one layer of H600 consists of two thinner layers of material that are readily separated (one blue layer and one white layer). That is, "2 layers H600" equates to four total layers of material (two separate blue/white layers).

the smallest particulate fraction (7-420 nm) of the concentrated SiO 2 nanoaerosol (1.4%). In all cases, filtration efficiency improved by adding a layer of H600 or vacuum HEPA material and improved further upon adding a second layer of the same material. Two layers of H600 achieved the greatest level of filtration, but also the greatest pressure differential. Consequently, two layers of H600 reduced airflow by the greatest margin (36%) and increased the breathing zone CO 2 concentration by nearly 2%.

Without modification, the Stryker Flyte helmet system is unsuitable for use as a PAPR, confirming warnings provided by the manufacturer and Derrick and Gomersall 3 . However, when modified as described herein, infiltration of particles measuring 0.3-25 μm in diameter was reduced by 99.9%. Particles measuring 7-420 nm were reduced by >98.5%. The greatest reduction in particles of all sizes was achieved using two layers of H600 material, a sterilization wrap found in hospital settings and used to demonstrate an N95-equivalent facemask. 11 The added material reduced airflow through the helmet, however, and allowed CO 2 inside the PAPR to stabilize at 2.3 ± 0.3% when worn by a volunteer. The increased differential pressure resulting from adding filter layers over the air intake of the PAPR helmet is expected to reduce the operational lifetimes of the helmet blower motor and battery, which further emphasizes the temporary emergency nature of the solution described. While healthcare providers should always seek PPE authorized for given tasks, the solution described offered a relatively simple approach to achieve enhanced protection against sub-micron particles during the earliest stages of the COVID-19 pandemic when supply chains were disrupted, and emergency PPE alternatives were critically needed. The solution was used by healthcare providers in the US who had no alternative PPE during treatment of COVID-19-positive patients. Further, our approach to develop and validate the experimental PAPR informs a need for new PAPR evaluation methods. 7 While the impact of the COVID-19 pandemic on PPE and supply-chains caught many healthcare providers off-guard, including the medical personnel who initiated and participated in the work described here, they can be better prepared for similar scenarios in the future based on the provisions of the NIOSH PAPR100 2 rule. The PAPR100 rule specifies test criteria and acceptable performance criteria for components and attributes of air-purifying particulate respirators. Provisions are included and/or modified for quantifying airflow resistance, exhalation valve leakage, filter efficiency, fit, total noise level, and related parameters. The silica dust loading test typically required for PAPRs has been excluded for the PAPR100 designation and may allow for PAPR designs that are better suited for healthcare settings. Additionally, a new low-flow warning device is designated only for PAPR100 class respirators and must alert users when breathing airflow falls below a certain threshold. 2 This work illustrates one of the many examples of innovative collaborative efforts that transpired between hospitals, institutions of higher learning, businesses, and state/ federal government during the earliest phase of the COVID-19 pandemic in the US, when PPE shortages persisted and supply chains were critically disrupted. As resources were directed to population centers, healthcare providers in small rural areas with increasing COVID-19 caseloads faced especially dire choices. Makeshift PPE solutions are never advisable and more innovative testing frameworks, such as the NIOSH PAPR100 rule, can help healthcare providers and public safety workers confront PPE shortages more effectively during future pandemics and public health emergencies.

Personal protective equipment needs in the USA during the COVID-19 pandemic

Approval Tests and Standards for Air-Purifying Particulate Respirators

Surgical helmets and SARS infection

Modification of stryker T5Ô and stryker flyte ® personal protection surgical helmets to function as powered air-purifying respirators

Airborne transmission of SARS-CoV-2

Stryker flyte suit -crown conversion for COVID 19

Development of a manikin-based performance evaluation method for loose-fitting powered air-purifying respirators

SiO 2 aerosol nanoparticle reactor for occupational health and safety studies

Testing of commercial masks and respirators and cotton mask insert materials using SARS-CoV-2 virion-sized particulates: Comparison of ideal aerosol filtration efficiency versus fitted filtration efficiency

Respirator Fit Testing Methods (ANSI/AIHA Z88.10-2001)

Repurposing surgical wrap textiles for use as protective masks during pandemic response

The authors acknowledge important contributions by Thomas Gravely, Andrew Cullip, Taylor Langon, Mark Rogers, Mike Goforth, Talmage Rowland, and Daniel Seitz.

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study is supported by the Virginia Tech Institute for Critical Technology and Applied Science (ICTAS) and NanoSafe, Inc.

Matthew S. Hull  https://orcid.org/0000-0002-5771-8481