Nelson S. Slavik is Senior Microbiologist and Vice President of Research and Development, CPAC Equipment, Inc. Responsibilities include research and development of infection control, patient safety, and sterilization technologies. Academically, he holds dual degrees from the University of Illinois at Urbana-Champaign, which include a Ph.D. in Microbiology and Master of Science in Biochemistry/Microbiology.  

Nelson S. Slavik, Sr. Microbiologist and VP of Research and Development, CPAC Equipment, Inc.

Figure 1. RH-Pro11 and RH-Pro9 HVHA Sterilizers

raditionally, steam sterilization has been the primary mechanism to sterilize dental and medical surgical instruments. However, advances in sterilization have provided another thermal sterilization technology that uses high-velocity hot air to effectively sterilize instruments in significantly shorter time periods without water, thus eliminating instrument drying and instrument corrosion.

With concurrent advances in heat-resistant materials, most dental and microsurgical instruments are compatible with the temperatures employed in the hot air sterilization process. Shorter sterilization processing cycles result in reducing expensive instrument investment and assuring efficient instrument use. Eliminating instrument corrosion provides a longer life span of delicate, costly instruments, lowering dental practice operating costs.

The resurgence of dry heat as a legitimate sterilization technology began in 1960 with work conducted by NASA for ensuring the sterility of lunar and planetary spacecraft. Conducted at the Army BioLabs at Fort Detrick, Maryland, under the direction of Dr Charles R. Phillips, this work led to the selection of dry heat as the only viable sterilization option for total sterilization of planetary and interplanetary spacecraft. Dry heat sterilization technology was first used on the Mars Viking 1 and 2 landers in the mid-1970s and continues to be used today as the primary method for sterilizing all planetary and interplanetary spacecraft, including the latest Mars lander, Perseverance.

Conventional passive and low-velocity dry heat sterilization has never gained popularity for medical instrument sterilization, primarily being limited by the lengthy sterilization times (1 hour at 340 °F; 1-2 hours at 320 °F) as required of the sterilization process. However, in the 1980s, Keith Cox, DDS, observed that increasing heated airflow to an instrument significantly increased bacterial spore destruction rates.

This observation inspired Dr Cox’sdevelopment of the patented Cox RapidHeat™ Sterilizer from CPAC Equipment, which resulted in a marked reduction in the time required for instrument sterilization, going from hours by conventional dry heat sterilization to minutes at 375 °F in the Cox RapidHeat Transfer Sterilizer. The device was granted 510(K) status from the United States Food and Drug Administration (FDA) in 1987 and 1988 as a Class II (performance standards) device.

Since then, High-Velocity Hot Air (HVHA) sterilization has been recognized and validated for use in health care applications including medical and dental offices, laboratories, ambulatory care clinics, and hospitals by the Centers for Disease Control and Prevention in their publications 

Guidelines for Infection Control in Dental Health-Care Settings—2003

Guideline for Disinfection and Sterilization in Healthcare Facilities (2008)

 Standards for use and process validation have been issued under the auspices of the American National Standards Institute and the Association for the Advancement of Medical Instrumentation in the standards ANSI/AAMI ST40:2004(R)2010 and ANSI/AAMI ST50:2004(R)2010.

There are 3 distinct types of dry heat sterilizers as distinguished by their degree of air convection, with “convection” being defined as the transfer of heat due to the bulk movement of molecules within fluids. Dry heat sterilizers utilize moving air as fluid to transfer heat from the air to medical instruments. These sterilizers are categorized as: (1) static or passive hot air sterilizers, in which air convection is generated solely by gravity as hot air rises and cooler air descends; (2) mechanical low-velocity forced-convection sterilizers, in which heated air is moved at less than 20 air changes per minute to minimize hot and cold areas within the chamber; and (3) HVHA sterilizers in which air is moved at a high rate, such as 200 air changes per minute, in which high-velocity flowing air amplifies the rate of heat conduction and improves the uniformity of temperature.

Dry heat functions to sterilize by transferring heat to the microorganism, causing the inability to reproduce due to DNA and enzymatic damage. Time-temperature profiles have been established for wrapped instruments, unwrapped instruments, and handpieces to deliver a sterility level of 6 log

 sterility assurance level (SAL) representing a total microbial inactivation level of 12 Log

sporesas required by FDA and ANSI/AAMI standards. CPAC Equipment’s Pro-Series HVHA™ sterilizers 

ure 1) operate at 375 °F under varying processing times, dependent on whether the instrument is unwrapped (12-minute exposure), wrapped (22-minute exposure), or within wrapped cassettes (40-minute exposure). Times expressed are from the start of the process to its completion. No drying cycle is required 

High-Velocity Hot Air Dental and Microsurgical Instrument Sterilization

The total instrument processing time is an additive combination of the time required to raise the instrument’s temperature to initiate spore kill and the time necessary to kill 6 log

 The instrument preheat time difference between unwrapped (6 minutes) and wrapped (10 minutes) is due to insulation barriers created by the nylon pouch and the associated entrapped air, which causes the time difference of 4 minutes in reaching the spore inactivation temperature on the instrument.

Once spore kill is initiated at the temperature of 313 °F to 315 °F, spores are killed at the same rate of 27 to 28 seconds per 1 log

 kill for unwrapped and wrapped instruments and for wrapped cassettes 

 The total processing time needed to meet the FDA-required 12-log

 kill is 5.6 minutes plus the required preheat time.

As with any thermal sterilization device, temperature compatibility with all intrinsic instrument components is imperative. For an HVHA sterilizer operating at 375 °F, most of today’s instruments and their components are constructed with materials that would not be subjected to damage at this elevated temperature. Standard handpieces, pliers, and cutters are typically composed of 440C stainless steel or other high-temperature–resistant metals (including solders). The temperatures used in dry heat sterilization whether static, low-convection, or HVHA processes do not contribute to corrosion or the stressors that dull, pit, or crack instruments. Surgical stainless steels used in biomedical applications are also used in industrial applications requiring thermal compatibility in excess of 2000 °F due to their ability to provide good strength and good resistance to corrosion and oxidation at these elevated temperatures.

For instruments that contain plastic or other nonmetal components, there may be susceptibility to repeated exposure of 375 °F, although most nonmetal components compatible with a steam sterilization process are also compatible with exposure to 375 °F. Changes in color, cracking, or other alterations in physical appearance are visible indicators that the elevated temperature is affecting the material and could alter the instrument’s performance.

In recent years, the creation of more heat-tolerant materials (eg, heat-resistant fluoropolymers and silicones) and their replacement of heat-intolerant materials used in medical devices has reduced significantly the number of instruments that are intolerant to the dry heat sterilization conditions. Dental handpieces contain bearing retainers and O-rings made of high-temperature–resistant materials (typically Torlon®, Viton™, phenolics, and polyimides) tolerant to 375 °F temperatures employed in the HVHA sterilizer. Temperature resistance for these materials is over 450 °F. Lubricants must be rated food-grade, withstand a temperature higher than 450 °F (eg, SteriLUBE™ or similar fluorinated synthetic), and not contain any hydrocarbon-based materials such as mineral oil to avoid any temperature incompatibilities. Results from a 2020 study by The Dental Advisor showed that there was no performance decrease in new and used handpieces tested after 250 sterilization cycles in the RH-Pro11 when using the fluorinated high-temperature cleaning and lubricant system, SteriKleen™ and SteriLUBE.

Significant with any hot air sterilization method is the dry conditions that minimize or eliminate instrument corrosion. With any chemical or steam sterilization method, chemicals and/or water react with metals and corrode. Corrosion affects the ability to properly sterilize an instrument and the instrument’s efficacy of use, resulting in shortening the effective lifetime of an instrument. Instrument exposure to chloride environments (eg, cleaners and disinfectants) is a primary source for pitting and cracking regardless of a wet or dry heat sterilization process. However, a wet heat sterilization process amplifies the corrosion process and significantly affects an instrument’s material integrity. On the other hand, dry heat sterilization is a moisture-free process that does not provide the conditions necessary to promote corrosion. The temperatures used in dry heat sterilization, whether static, low-convection, or HVHA processes also do not have an impact on corrosion or any other stainless steel stressor.

To minimize expensive instrument inventory and ensure efficient instrument use requires a quick turnaround of instruments from one patient to the next. Often, instrument sterilization is the most time-consuming operation in the preparatory process. All thermal sterilization processes are time and temperature dependent, and sterilization times cannot be cut to expedite the process. Comparison of times required of steam sterilization and HVHA sterilizers must accurately reflect the total time required from when the instrument is placed into the sterilizer until the time it is removed. Complete steam sterilization processing time includes (1) the time necessary to achieve the required temperature and pressure (2) the sterilization cycle time and (3) instrument drying cycle time.

HVHA sterilizers were developed primarily for use within dental clinical practices, and as such, the sterilizers are small, designed for tabletop use (Figure 1

 or to be portable by placement on a moveable cart. HVHA sterilizers typically operate on 110 to 120 V or 220 V. They are energy efficient (ie, 1400 watts for the initial warm-up stage at the beginning of the day and 300 watts during the sterilization cycle). HVHA sterilizers require no water or stream for operation, making their placement contingent only on the availability of conventional or field-generated electricity.

Standard controls minimize error and make the operation of the unit easy for dental or medical staff. Controls are limited to an on/off switch and preprogrammed cycle time designations (eg, wrapped, unwrapped, or handpieces). Operationally, the sterilizer is turned on at the beginning of the day and turned off at the end. The sterilizer typically requires approximately 15 minutes to initially heat to operational temperature. Once the chamber is at operational temperature, the sterilization cycle is automatically initiated. The operator is notified at the completion of the cycle, and the instruments are removed from the unit and allowed to cool before use. (Figure 3 for automated operational screen sequence). All sterilization cycle data are internally stored and retrievable through a flash drive for computer or hardcopy documentation.

Use of the RH-Pro11 and RH-Pro9 for N95 Respirator Decontamination

The use of HVHA technology was investigated for use to decontaminate N95 respirators and masks for reuse during their severe shortage caused by the coronavirus disease 2019 (COVID-19) pandemic. Published peer-reviewed reports have demonstrated that dry heat processing is the preferred method to assure that both viral inactivation and N95 respirator performance efficacies are maintained for numerous reuse cycles.

CPAC Equipment, Inc, has repurposed their RH-Pro11 and RH-Pro9 sterilizers for N95 mask reprocessing by developing a dedicated decontamination cycle based on a documented time-temperature parameter of 176° F for 30 minutes to inactivate severe acute respiratory syndrome coronavirus 2 cells without interfering with mask filtration and breathability performance for up to 20 reuses. RH-Pro11 and RH-Pro9 units can process up to 96 and 24 pouched masks per hour, respectively. Repurposing RH-Pro11 and RH-Pro9 sterilizers for respirator decontamination is performed by a simple flash drive upload of N95 mask decontamination software. A similar process using the appropriate RH-Pro11 or RH-Pro9 software will convert these units back to their original sterilization function. The RH-N95 Decontamination System meets the FDA criteria for emergency use authorization during the ongoing COVID-19 crisis.

HVHA sterilization technology is an excellent instrument sterilization option for any dental practice. A moisture-free and water-free environment eliminates instrument corrosion issues that dull and limit the useful life span of the delicate instruments used in dentistry. The short sterilization cycles and the elimination of drying provide a rapid turnaround of instruments, resulting in timely availability for the next patient and minimizing instrument inventories. Preset time-temperature parameters and automatic controllers ensure sterilization for each cycle. These sterilization parameters are recorded and stored within internal memory for retrieval via a USB port for external storage or hard copy printouts, providing the data necessary to document sterilization conditions for each treatment cycle. ●

1. Kohn WG, Collins AS, Cleveland JL, Harte JA, Eklund KJ, Malvitz DM. Guidelines for infection control in dental health-care settings–2003. Centers for Disease Control and Prevention. December 9, 2003. Accessed June 6, 2013. 

http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5217a1.htm

2. Guideline for disinfection and sterilization in healthcare facilities (2008). May 24, 2019. Accessed June 6, 2013. 

https://www.cdc.gov/infectioncontrol/guidelines/Disinfection/index.html

3. Table-top dry heat (heated air) sterilization and sterility assurance in health care facilities. Advancing Safety in Health Technology. January 12, 2018. 

https://my.aami.org/aamiresources/previewfiles/ST40_reaff_2018_preview.pdf

4. American National Standards Institute and the Association for the Advancement of Medical Instrumentation “Dry heat (heated air) sterilizers,” ANSI/AAMI ST50:2004(R)2010. Accessed October 15, 2014.

5. Design guidelines for the selection and use of stainless steel. Nickel Development Institute. 

https://nickelinstitute.org/media/1667/designguidelinesfortheselectionanduseofstainlesssteels_9014_.pdf

6. Cowen M, Powers JM. HVHA RH-Pro11 sterilization effect on handpiece performance. Dental Advisor. January 28, 2020. https://www.dentaladvisor.com/pdf-download/?pdf_url=wp-content/uploads/2020/03/Vol_37-02-Curing-Lights_WHOLE-ISSUE_v3.pdf 7. Enforcement policy for bioburden reduction systems using dry heat to support single-user reuse of certain filtering facepiece respirators during the coronavirus disease 2019 (COVID-19) public health emergency. US Food and Drug Administration. November 25, 2020. 

https://www.fda.gov/regulatory-information/search-fda-guidance-documents/enforcement-policy-bioburden-reduction-systems-using-dry-heat-support-single-user-reuse-certain

Articles

High-velocity hot air sterilization systems provide optimal sterilization for dental instruments and eliminate corrosion.

Information provided by CPAC Equipment, Inc

During these trying times, one common obstacle has been a shortage of personal protection equipment (PPE), including the medical-grade N95 masks needed by healthcare providers and first responders.

That’s why it was a big deal when CPAC Equipment, Inc., recently began offering the RH-N95 Decontamination System to help the healthcare industry overcome and alleviate their N95 mask shortages.

The use of High-Velocity Hot Air (HVHA) technology has been investigated as a mechanism to decontaminate N95 respirators and masks for re-use during their severe shortage caused by the COVID-19 pandemic. Published reports have demonstrated that dry heat processing is the preferred method to assure that both viral inactivation and N95 respirator performance efficacies are maintained for numerous re-use cycles.

Because of this, CPAC Equipment has repurposed its RH-Pro11 medical/dental sterilizer for N95 mask reprocessing, developing a dedicated decontamination cycle based on documented time-temperature parameters necessary to inactivate coronavirus without interfering with mask filtration and breathability performance for up to 20 re-uses.

This countertop unit can process approximately 100 masks per hour and can be located anywhere within a dental clinic or hospital, requiring only 110-115/12A service for its operation. The RH-N95 Decontamination System meets the FDA criteria for emergency use authorization during this crisis, with permanent 510(k) status to follow upon completion of microbial kill efficacy testing.

The COVID-19 pandemic has induced critical shortages of N95 masks which are used as the primary first line of defense to stop the virus from entering the respiratory system and manifesting disease. The world was not prepared for the magnitude of this crisis, resulting in the use of inadequate masking or the attempt to decontaminate a previously used mask. For the latter to be successful in the decontamination process, the mask must be assured to have met the criteria for coronavirus destruction and for the maintenance of the mask’s original performance standards.

The FDA has recently released its guidance document entitled “Enforcement Policy for Sterilizers, Disinfectant Devices, and Air Purifiers During the Coronavirus Disease 2019 (COVID-19) Public Health Emergency” (FDA

), which provides the guidance to provide the necessary safeguards of devices for mask re-processing. Meeting these FDA recommendations will allow devices not yet receiving the usually required FDA clearances to enter the market safely to relieve the N95 shortage. FDA emergency use authorization only grants authorization for previously cleared sterilization and disinfection devices which have been temporarily repurposed for decontaminating N95 respirators. No authorization has been granted by the FDA for devices that are used in the control of hospital acquired infections (HAI’s) such as UV room disinfectant units or other repurposed devices or technologies that have not been issued a 510(k) as a sterilization or disinfection device. 

The CPAC RH-N95 meets those criteria, allowing the unit to enter the market under the FDA’s emergency authorization until final quantitation testing is complete for the issuance of an FDA 510(k). Until that work is completed, recognized (peer-reviewed literature) decontamination parameters for coronavirus inactivation and Mycobacterium inactivation allow the use of the RH-N95 as a decontamination device. This decontamination technology does not introduce any chemicals to the mask, nor does it affect the mask’s performance for breathability and filtration prescribed for the N95 mask performance by ASTM. 

The CPAC Equipment RH-Pro11, which has been repurposed to the RH-N95, differs from the traditional dry heat sterilizer in which air remains static (air movement only by gravity convection) or in which air is minimally re-circulated by mechanical convection to enhance heat distribution. High-velocity hot air technology employs directed, uniform high-velocity hot air across the surface of a medical device which enhances heat transfer. As a heat conduction process, this thermodynamic mechanism heats and sterilizes/decontaminates both the surface and the solid interior of the device, including residues that may still be retained. The result is a marked reduction in time required for medical device sterilization or decontamination from hours to minutes by traditional dry heat sterilization. 

The original Cox RapidHeat™ Transfer sterilizer serves as the predicate device to the RH-Pro11 and was granted 510(k) status from the FDA as a Class II (Performance Standards) device issued under K872643A and K881371. The RH-Pro11 sterilizer has been designed to sterilize medical instruments at temperatures of 375°F for 6-minute (unwrapped) and 12-minute (wrapped) cycles. High-velocity hot air sterilization has since been recognized and validated for use in healthcare applications including medical and dental offices, laboratories, ambulatory care clinics, and hospitals by the Centers for Disease Control and Prevention in their publications “Guidelines for Infection Control in Dental Health-Care Settings-2003” and “Guideline for Disinfection and Sterilization in Healthcare Facilities, 2008.” Standards for use and process validation have been issued under the auspices of the American National Standards Institute and the Association for the Advancement of Medical Instrumentation in standards ANSI/AAMI ST40:2004(R)2010 and ANSI/AAMI ST50:2004(R)2018. 

The high-velocity hot air process eliminates issues otherwise found in other thermal, chemical, or UV decontamination methods. Treatment mechanisms that introduce liquids to the mask run the high risk of severely lowering the mask’s filtration and breathability performance (Liao). This is especially true of water or water vapor that destroys the electrostatic nature of the mask’s filtration fabric which gives it the ability to meet its stated performance level. This would include steam sterilization and any liquid disinfection method. Chemical liquid/gas phase disinfection/sterilization technologies also introduce issues with: 

Incompatibilities of mask materials with the disinfectant/sterilant (includes electrostatic performance, band elasticity; adhesive performance, and metal reactions)

Providing uniform concentration of the introduced (and maintenance of) required disinfectant/sterilant concentration

Mask fiber matting and required filtration and breathability performance

Toxic chemical residue retention and the ability to eliminate residues and monitor their removal

UV is not reliable due to its inability to penetrate the deep mask fibers and the “shadowing” interferences from mask fibers and dust residues that preclude the UV from contacting pathogens. No FDA-cleared UV sterilizers/disinfectors are known to be available, except for their use in mitigating hospital-acquired infections.

High-velocity Hot Air technology provided through the RH-N95 offers a simple mechanism that provides a relatively low, uniform temperature (155°F; 68°C) and a moderate exposure time of 30 minutes to decontaminate masks from coronavirus and other pathogens. Documented, peer-reviewed literature offers ample guidance in the temperature and exposure time required to inactivate coronavirus and other pathogens. No drying or residue removal is required of the process and at the relatively low temperatures required, little or no change in mask performance is expected.

Data from peer-reviewed literature provides a strong indication of those temperatures and exposures that are prescribed for the RH-95 can inactivate coronavirus and will maintain structural integrity and performance of the re-processed N95 respirator. This data has been instrumental in the construction of a decontamination cycle that should provide > 6 Log

 reduction (>99.9999 percent reduction) as demonstrated by Rabenau et al. 

(See references for additional information)

 for SARS-Co-V and Mycobacteria (Sung and Collins) at 60°C for 30 minutes. Rabenau et al. noted that heat treatment at 56°C for 30 minutes reduced a >7 Log

 SARS virus concentration to below the detection limit. Processing at 60°C for 30 min resulted in no infectious virus remaining (>7 Log

 reduction), regardless of the presence of any protein. 

This data is also consistent with data provided by the World Health Organization for coronavirus (SARS) demonstrating an extrapolated 6 Log10 reduction in 22.5 minutes at 56°C (133°F). The data gleaned from these references leads us to believe that temperatures between 65-72°C (149-162°F) are adequate to fully inactivate the coronavirus (>6 Log

 reduction) at an exposure of 30 minutes without damage to mask components or to the mask’s performance. Although these microbial concentrations would seldom or ever be seen on a mask, these reduction levels provide the margin of safety necessary for mask re-use (FDA). 

The studies presented above come from observations with liquid viral suspensions heated to temperature with various exposure times. However in a study by McDevitt et al. with inactivation of H1N1 virus on glass and stainless steel surfaces, it was demonstrated that with dry heat temperatures of 60°C and 65°C, this virus could be inactivated to the limits of detection at >5 Logs at 30 minutes exposure. This inactivation level is above the threshold required presently by FDA of > 3 Log

. This data supports the time-temperature parameters seen in the previously stated studies and supports the re-processing time and temperature prescribed for the N95 mask cycle. 

The FDA is requiring that Mycobacterium inactivation be assessed, recommending a >6 Log

 reduction. Mycobacterium represents the most heat resistance of microbial species (other than spores and prions) and is used as the demonstrative surrogate for inactivation of other vegetative bacteria and of fungi, parasites, viruses, and Mycobacterium. The demonstration of >6 Log

 reduction of Mycobacterium would further assure user safety from the destruction of other pathogens that might accompany a used mask.

Literature searches have demonstrated that 

, can be inactivated in solution to a >6 Log

 reduction in 6 minutes at 65°C (149°F) and at 68°F (155°C) in 2.2 minutes. 

, the heat-resistant surrogate designated for Mycobacterium challenge inactivation studies. The time-temperature profiles selected for N95 mask re-processing exceed those profiles required to inactivate >6 Log

For completion of the requirements necessary for an FDA-clearance, testing will be conducted using a coronavirus surrogate such as a Murine Hepatitis Virus or Human Coronavirus 229-E to assure the coronavirus is inactivated by >3 Log

).  Additionally, testing will be conducted to assure a reduction of >6 Log

 can be achieved on a Mycobacterium species to denote the destruction of other microbiological pathogens that may have also contaminated the mask during its use. These studies will be initiated shortly to meet FDA 510(k) marketing clearance requirements.

Inherent for the re-use of an N95 mask is the requirement to assure that the decontamination process does not jeopardize the safety and health of the healthcare practitioner re-using the N95 mask. N95 respirators/masks are commonly made of nonwoven fabric consisting of three composite layers: Outer-layer consisting of spunbond polypropylene; mid-layer consisting of meltblown polypropylene; and an inner-layer consisting of spunbond polypropylene). Some N95 respirators also incorporate an additional layer of cellulose/polyester nonwoven, the outer active layer coated with a hydrophilic plastic laminated to a second inner layer treated with copper and zinc ions. This additional dual layer is designed to inactivate influenza viruses using deferent mechanisms of action. Those masks containing this additional inactivation layer containing cellulose is incompatible with hydrogen peroxide re-processing technologies. 

The polypropylene, polyester, and cellulose components all are compatible with the HVHA process employed in the RH-N95, including the retention of the electrostatic charge in the polyethylene layers. Typically, the other components of N95 masks are also thermally compatible with the lower temperatures associated with the HVHA process: (e.g., straps composed of thermoplastic elastomers; nose clip made from aluminum; nose foam derived from polyurethane; and thermally resistant adhesives).

Specification performance of the mask’s integrity, composition, filtration and breathability are physical parameters that require analysis after the mask has been re-processed (FDA

). All visible indications from testing conducted by CPAC demonstrate the masks have not been altered by the decontamination process after twenty 30-minute re-processing cycles, the limit of the number of cycles conducted to date.

Observations are consistent with a report from Stanford University, which reported that after the N95 filtration fabric was dry heat-treated at 75°C for 30 minutes after 20 cycles there was no change in filtration efficacy or pressure drop. Whole mask studies after 20 cycles at this time and temperature also showed no deformations in the mask or changes in elasticity of face/ear straps (Liao). To demonstrate the maintenance of the recognized performance testing for filtration efficacy and breathability, masks undergoing 20 re-processing cycles will be tested against ASTM Standard criteria under F2100 in accordance with documentation required for 510(k) FDA-clearance.

The RH-N95 consists of four trays each capable of holding 12 N95 masks (nested, double-stacked), allowing ninety-six N95 masks to be processed in just over an hour. The decontamination cycle time for N95 decontamination is presently set at 30 minutes at a temperature of 68°C (155°F) in accordance with the parameters gleaned from the literature cited above. Total processing time is 34 minutes to allow for mask pre-heating before the decontamination cycle initiates. There is no water used in the process so the masks are dry at retrieval. The unit runs on 110-115V, 12 amps or 220-230V, 6 amps. It is a countertop unit and requires no other utilities, allowing mask processing to occur department-by-department or floor-by-floor. 

The RH-Pro11 has been reconfigured to the RH-N95 to accommodate these mask-required re-processing temperatures of 155-156°F. Changes in software have enabled CPAC to create a specific cycle for mask decontamination. The graph in 

 is thermocouple temperature data (Labjack T7-Pro, T-Type thermocouples) derived from two N95 3M 8210 masks nested together under full load conditions, one thermocouple on the outside mask (Series 2) and the second on the inside mask (Series 1). Arrows indicate Process Start (left), Decontamination Cycle Initiation (middle), and Process Finish (right).

 these cycle parameters meet all conditions that allow the masks to retain its specifications and function and provide the necessary viral kill levels to assure mask reliability and safety in its re-use. Temperatures do not exceed 69°C (156°F) with a temperature range of 155-156°F from 4 minutes into the cycle to completion of the 30-minute decontamination cycle (total 34 minutes from start of processing to finish). These time-temperature profiles are identical to single, non-nested masks, assuring nested masks present no barrier to high-velocity hot air technology.

These conditions will allow the RH-N95 to process up to 48 masks per 30-minute cycle or approximately 100 masks per hour, enabling healthcare facilities to meet the demand for N95 masks placed on them by this epidemic. Two models of N95 masks have been tested for repetitive re-processing at this time: 3M N95 8210 and Kimberly-Clark Corporation PFR95. It should be further noted that by visual inspection, no heat incompatibilities were found through 20 cycles of re-processing in the elastic bands, foam nose fittings, and adhesives to detract from secure and form fit to nose and face. 

We have demonstrated that an approach to replacing CIs with the CIR does provide the time and temperature data far superior to that of a CI. The CIR is placed onto a tray within the RH-N95 unit, generating the graph shown in 

. Tabular data is also generated and computer stored. Data retrieved is within one degree Fahrenheit of that data retrieved from the Labjack thermocouple data (described previously) once the CIR data logger has had the opportunity to come to temperature about eight minutes into the cycle. 

It should be noted that the time required for decontamination of the N95 masks in the RH-N95 may be significantly lower than the 30-minute exposure time derived from the literature. HVHA technology employed in the RH-Pro series of sterilizers has been demonstrated to reduce exposure times by 80% when compared to traditional static (non-moving) air of dry heat sterilizers or dry heat ovens. Initial microbial inactivation studies by CPAC will use parameters found in the literature for its initial cycle settings. However, investigations will continue to determine if lower exposure times can provide a more expedited decontamination process. 

The RH-N95 has been allowed to begin marketing under the recent FDA Enforcement Policy for Sterilizers, Disinfectant Devices, and Air Purifiers During the Coronavirus 2019 Public Health Emergency document (FDA

). Based on documented evidence that coronavirus can be inactivated at a >5Log

 reduction at 155-156°F with an exposure of 30 minutes, a dedicated N95 mask treatment cycle was created for RH-N95. The time-temperature parameters utilized appear to cause no physical damage or inhibit mask filtration/breathability performance. Studies will soon be underway to quantify viral inactivation and mask performance in accordance with FDA 510(k) marketing clearance requirements.

Nelson S. Slavik is Senior Microbiologist and Vice President of Research and Development, CPAC Equipment, Inc. Responsibilities include research and development of infection control, patient safety, and sterilization technologies. Academically, he holds dual degrees from the University of Illinois at Urbana-Champaign, which include a Ph.D. in Microbiology and a Master of Science in Biochemistry/Microbiology.  He has consulted to the American Hospital Association as their primary environmental regulatory consultant for over 10 years providing testimony to Congress and providing workshop presentations nationally and internationally. He has authored over 80 articles on environmental/occupational safety and infection control, participating in over 100 workshops and seminars. He holds two patents on High-Velocity Hot Air technology.

Centers for Disease Control and Prevention. Required information for effective infectious disease outbreak response SARS-Cov-2 (Covid-19) Updated 3/4/2020. https://www.dhs.gov/sites/default/files/publications/2020_03_18_mql_covid-19-sars- cov-2_-_cleared_for_public_release_0.pdf 

, Enforcement Policy for Sterilizers, Disinfectant Devices, and Air Purifiers During the Coronavirus Disease 2019 (COVID-19) Public Health Emergency. 

https://www.fda.gov/regulatory-information/search-fda-guidance-documents/enforcement-policy-sterilizers-disinfectant-devices-and-air-purifiers-during-coronavirus-disease?utm_campaign=2020-03-29%20FDA%20Issues%20New%20Enforcement%20Policy%20for%20Sterilizers&utm_medium=email&utm_source=Eloqua

, Enforcement Policy for Face Masks and Respirators During the Coronavirus Disease (COVID-19) Public Health Emergency: Guidance for Industry and Food and Drug Administration Staff, March 2020. 

https://www.fda.gov/regulatory-information/search-fda-guidance-documents/enforcement-policy-face-masks-and-respirators-during-coronavirus-disease-covid-19-public-health

McDevitt, J et al., Role of Absolute Humidity in the Inactivation of Influenza Viruses on Stainless Steel Surfaces at Elevated Temperatures. Applied and Environmental Microbiology 76:12 (pgs. 3943-3946) 2010.

Liao, L et al., Can N95 facial masks be used after disinfection? And for how many times? Report from the collaboration of Stanford University and 4C Air, Inc., March 25, 2020. 

https://stanfordmedicine.app.box.com/v/covid19-PPE-1-2

Rabenau, HF, et al., Stability and inactivation of SARS coronavirus. Med Microbiol Immunol 194: 1–6 (2005). 

https://www.researchgate.net/publication/8586211_Stability_and_inactivation_of_SARS_coronavirus

Sung, N and Collins, MT, Thermal Tolerance of Mycobacterium paratuberculosis. Applied And Environmental Microbiology, Mar: 999–1005, 1998. 

World Health Organization. First data on stability and resistance of SARS coronavirus compiled by members of WHO laboratory network. 

https://www.who.int/csr/sars/survival_2003_05_04/en/

Continue reading for more details and features of the HVHA RapidHeat

Summary of CPAC Equipment’s HVHA RapidHeat™ RH-N95 Mask/Respirator Re-processor

Reconfigured from CPAC Equipment’s RH-Pro series of FDA-cleared sterilizers, the RapidHeat RH-N95 Mask/Respirator Re-processor has been designed to decontaminate N95 respirators, to counteract the severe shortage of N95 masks during this pandemic. The RH-N95 offers the following features/advantages over other thermal, chemical, and radiological alternatives as listed below.

Preferred decontamination process (Stanford Report, March 2020), that provides documented evidence of maintaining filtration and breathability performance (no electrostatic charge reduction in meltblown fibers used as viral filtration fabric)

Meets or exceeds published (peer-reviewed) >6 Log

 reduction requirements for coronavirus and Mycobacterium to assure coronavirus kill and that of other non-spore pathogens as well

Meets FDA criteria to market device for coronavirus decontamination under FDA’s emergency authorization

Dedicated unit for the re-processing of N95 respirators/masks

Requires no water in its operation; requires only 110-115V/220-240V electric service that is commonly available

No ancillary chemical or other treatment or supply products required

No drying time required after treatment; masks are cool to the touch in seconds after their removal from the unit and ready for immediate re-use

No residues to evacuate from treated masks after treatment; no worry about lingering toxic chemical residues to sensitive nasal passages, facial skin, and other respiratory passages

Ability to monitor decontamination parameters (time-temperature). Other non-thermal processes have no method to measure chemical concentrations at site of required kill

No deformation in mask structure or change in filtration/breathability performance for at least twenty (20) re-use cycles

Low cost for RH-95 Mask Re-Processor (~ $7,500)

Multi-purpose unit that functions as N95 mask re-processor, but can be simply re-programed via USB port to be used as a medical/dental sterilizer (FDA-cleared) post-pandemic

Countertop unit with small footprint which can be placed almost anywhere electrical service is available

Four-tray configuration allowing approximately 100 masks to be processed per hour

CPAC Equipment recently began offering the RH-N95 Decontamination System to help the healthcare industry overcome and alleviate their N95 mask shortages. 