At about the same time that the Citomat was under development, AMSCO (now Steris) was working on a rather larger, and much more sophisticated, closed-loop, hydrogen peroxide gassing system that was named Vapor Hydrogen Peroxide (VHP) 1000. Figure 7.8 shows a VHP 1000 together with a flexible film isolator. This unit introduces a new step in the gassing cycle, by first drying the air in the isolator system using a chemical bed. This allows a much greater concentration of vapour to be carried in the air without condensation developing, and makes the initial relative humidity and temperature of the air in the isolator practically irrelevant.
Hydrogen peroxide is flash evaporated into the dry airstream from 30 percent (100 volume) solution. The resulting gas is passed around the isolator to be treated and then returned to the generator, which contains a catalyst bed. This breaks down the gas to water vapour and oxygen to complete the cycle, and forms a closed-loop system with no environmental emission. The hydrogen peroxide solution is supplied by Steris in special, sealed cartridges that fit into a compartment on the front of the machine, so that the operator does not have to handle the material at any stage. The control system
provides a digital readout of the cycle parameters, which can be downloaded to a PC, and emphasis is placed on the ease with which the system can be validated to FDA requirements. The manufacturer says that the VHP 1000 can handle isolator volumes up to 30 m3, which is very large in isolator terms. As a result of these advanced features, the VHP 1000 has sold well and is to be found in pharmaceutical plants throughout the world, not only for use in isolator sterilisation but in other applications as well.
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