VHP takes its place in room decontamination
11/01/2001
Case Study
AUTOMATED DECONTAMINATION METHODS FOR CLEANROOMS ARE BECOMING A MORE WIDELY ACCEPTED PRACTICE. IN THIS CASE STUDY, DRY STERILIZATION IS PUT TO THE TEST.
by Anders Malmborg, Maria Wingren, Philippe Bonfield and Gerald McDonnell
 Surface damage due to hydrogen peroxide condensation. Condensation should not occur during the VHP7 decontamination process if adequately controlled. |
Avariety of methods and antimicrobial agents have been used for the periodic decontamination of critical environments. Conventional wipe down techniques with antimicrobial products can be time consuming and labor intensive, while traditional fumigation with formaldehyde is slow and carries safety concerns.1
Automated decontamination methods are becoming more widely used. Vaporized Hydrogen Peroxide (VHP7) is being used for decontaminating a wide variety of rooms and is becoming accepted as an environmentally friendly alternative to formaldehyde.2 In this report, the STERIS VHP 1000, a mobile VHP7 generation, control and delivery system, was utilized and a typical cleanroom application is presented.
 The VHP1000 mobile unit |
Dehumidification, conditioning, sterilization and aeration
The typical VHP7 cycle consists of four phases: dehumidification, conditioning, sterilization and aeration. During dehumidification, the relative humidity is reduced, by drying, to a range of 10 percent to 30 percent by circulating the air in a closed loop. During conditioning, VHP7 is produced by vaporizing 35 percent liquid hydrogen peroxide and then introducing it into the recirculating air stream to rapidly achieve the desired VHP7 concentration.
The sterilization phase proceeds identically to the conditioning phase, but at a steady-state injection and recirculation flow rate to maintain the VHP7 concentration for the desired exposure time. The vapor is sporicidal at low concentrations (typically 1-2 mg/L at 25°C), in contrast to the liquid hydrogen peroxide.3
The VHP7 concentration is maintained below the condensation point to prevent condensation of H2O2 on the room surfaces and may therefore be referred to as a >dry= process.
The vapor concentration is maintained at a constant level by continually introducing VHP7 into the incoming air and removing it by catalytic degradation from the returning air line over the programmed exposure cycle. During the aeration phase, the residual peroxide vapor in the room is decomposed into non-toxic byproducts (water vapor and oxygen) by recirculation through a catalytic converter. Using the room ventilation system during this phase may significantly reduce room aeration times. In this case, the VHP7 1000 microprocessor continuously monitors and/or controls the process parameters during each cycle; the cycle parameters are recorded and printed out during the cycle for reference and cycle documentation.
 |
Ferring Pharmaceuticals utilized VHP7 decontamination for 10 rooms used for vial, ampule and syringe filling, sterile filtration, cold storage and gown changing. Previously, the rooms were decontaminated using conventional wipe down techniques. In order to supersede the traditional method, the replacement decontamination process needed to have these characteristics:
- Be compatible with room finishes and equipment
- Be safe to use
- Leave no process residuals
- Be validatable
- Provide documentation
- Allow for personnel to work in surrounding areas during the decontamination of an individual room.
Room size varied from 9 m3 (317 ft3) to 89 m3 (3142 ft3). These rooms included aseptic filling suites, filtration rooms, transfer and change areas and a cold storage room. With the exception of a cold storage room, which had its own recirculating air handling unit (AHU), the other rooms had single-pass-through air—100 percent fresh air. This presented the opportunity to reconfigure the AHU so that an individual room could be isolated while the other rooms remained functional. The AHU was slightly modified so that the exhaust from the room being decontaminated could be sealed while the air supply was used to slightly pressurize the area.
The air pressure difference could be maintained to enable the decontamination of a room while simultaneously allowing work to continue in adjacent areas. The VHP7 1000 was connected to each room, and individual cycles were developed with consideration given to temperature distribution and room size. An important consideration was to ensure adequate airflow in the room, with the assistance of air fans.
An example of a typical decontamination cycle for a larger syringe filling room (65 m3) follows:
_______________________
Dehumidification: Airflow: 32 m3/hour, Time: 15 minutes, Humidity: 6.9 mg/L (30% RH @ 25°C).
Note: Dehumidification was actually achieved prior to the cycle using the air handling unit; however, a short dehumidification phase was programmed to warm up the vapor inlet.
Condition: Airflow: 32 m3/hour, H2O2 injection: 9 g/min, Time: 20 minutes
Sterilization: Airflow: 32 m3/hour, H2O2 injection: 7g/min, Time: 100 minutes
Aeration: Done with air handling system.
_______________________
The room was cleaned before decontamination and all intrinsic equipment in the room remained during cycle validation.
VHP7 is a dry sterilization process, which is safe for use on a wide variety of surfaces, including electronics. The rooms walls and floor had an epoxy paint finish and the ceiling had a paint finish; the room also included stainless-steel paneling and PVC curtaining.
The decontamination cycle was developed to prevent the condensation of hydrogen peroxide on contact surfaces. A preliminary study at an intentionally higher hydrogen peroxide injection rate resulted in hydrogen peroxide condensation and room surface damage, which demonstrated the adverse affects if the process was not adequately controlled. Following optimization according to the VHP71000 cycle development guide, no further condensation or material incompatibilities were observed.
For the room described above, the decontamination process was validated using VHP7 chemical and biological indicators (105 Bacillus stearothermophilus spores.) An initial vapor distribution cycle was evaluated using the VHP7 chemical indicators to study the distribution of hydrogen peroxide vapor around the enclosed room. Twenty-one chemical indicators were placed at various locations in the room, including the floor, walls, ceiling, under benches or tables, and around the syringe-filling equipment. Following the exposure cycle, all indicators were recovered and indicated the presence of the sterilant.
A subsequent cycle was evaluated for decontamination validation with biological indicators, also randomly distributed around the room as described previously. Following the decontamination cycle, the biological indicators were aseptically transferred into growth media (tryptic soy broth) and incubated at 56°C. All exposed biological indicators were negative—no growth—following incubation. Similar decontamination cycles have been developed and validated for the other critical rooms in the facility.
In conclusion, VHP7 provided a rapid, effective and validatable decontamination method for critical rooms. The process was compatible with room finishes and equipment when adequately controlled, and left no post-process residuals. Room decontamination was performed unattended and allowed operations to continue in surrounding areas.
Anders Malmborg, Ph.D., is head of pharmaceutical production for Ferring AB, Limhamn, Sweden; Maria Wingren is a process engineer for Ferring; Philippe Bonfield, Ph.D., is based in the UK and is applications engineer for STERIS Corp., Mentor, OH; Gerald McDonnell, BS, PhD is senior manager, research and development for STERIS.
References
- Peters, J., and G. Spicher, 1981. "Room disinfection by formaldehyde vaporization," Hygiene Medecine, 6: 337-344.
- Jahnke, M., and G. Lauth. 1997. "Biodecontamination of a large volume filling room with hydrogen peroxide," Pharmaceutical Engineering, 17: 96-108.
- Block, S.S. 1991. Peroxygen compounds, p. 167-181. In, S.S. Block (ed.), Disinfection, Sterilization, and Preservation. Lea & Febiger, Philadelphia, PA.