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DECONTAMINATION


prolonged contact with the skin can cause bleaching or ulcers and the vapour can affect the respiratory system and irritate the eyes. In comparison to ethylene oxide the time-weighted average (TWA) exposure limit is five times greater, although it is not considered carcinogenic. (see Fig. 1) The transportation of high


regulated and the neat chemical is diluted with water by manufacturers to a typical concentration of between 50% and 60%. This reduces both the transportation requirements and the risk. The risk is further reduced by the use of small individual cartridges. The cartridges are hermetically sealed and are a single use unit, either in respect of one cartridge per cycle or a single use cartridge containing a number of charges for multiple cycles. At the end of the cycle any residual chemical in the single cycle cartridge is flushed out and into the drain and diluted to safe levels. With the multi-charge type, the life span is limited once pierced, and will be rejected when lapsed with the chemical being disposed of within the machines environment. The machines are programmed to reject any cartridges for which an attempt is made to reuse.


concentrations of H2O2 is strictly


Pressure mTorr


Time


Figure 2: The cycle presently offered on the Sterrad 100 and NX series involves pulling down to a low vacuum in the region of 300 mTorr.


labels and packaging cannot be used. Poor preparation, presentation and loading of products can also impact on the sterilisation process.


O2


Other risks Items to be processed in these machines need to be carefully selected and tested. Hydrogen peroxide will chemically attack a number of materials including precious metals, some aluminium and plastic products and will react violently with others. Additionally, cellulose will absorb the H2


so paper products for


example ethylene oxide and formaldehyde – is the repetition of the gas diffusion and sterilisation hold. Although this is to some extent optional, through cycle selection, it increases the assurance, when devices with lumens are being processed, of achieving sterility.


If the machine utilises the single cycle use


The cycle profile As with other gas sterilisation processes, the cycle is a combination of air removal, load preconditioning, gas admission and diffusion, sterilisation hold and removal of residual chemicals. The whole process is completed sub-atmospherically and at low temperature, below 60°C A deviation from other gas sterilisers – for


cartridge, it contains sufficient chemical to complete the two phases so the only advantage to a single sterilisation phase, is time, as the remaining chemical will be disposed of at the end of the cycle. It would, therefore, be a recommendation that the default cycle is the double sterilisation phase. A single phase cycle would only be recommended for surface sterilisation. A typical cycle would consist, depending on the manufacturer, of all or some of the following stages: • A pre-cycle dielectric check • Pre-vacuum • Pre-plasma • 1st


stage air removal • Gas admission/diffusion


‘Further research is required to fully understand the process, but it can be shown that the combination of low vacuum, hydrogen peroxide and plasma does in fact produce a sterilising environment.’


IFHE DIGEST 2014


• 1st • 1st


stage sterilisation hold stage air flush


• Plasma • 2nd


stage air removal


• Gas admission/diffusion • 2nd • 2nd


• Post vacuum • Plasma • Flushing • Plasma • Flushing • Vacuum break


Pre-plasma conditions and heats the load, and post-plasma breaks down the hydrogen peroxide into harmless water and hydrogen residues. Where the plasma is generated by an


internal grid, a significant safety feature is a check of the integrity of the grid. It is important that no part of the load, especially any items which are electrically conductive, does not short this grid to the chamber wall as high voltage is used to produce the plasma. An important part of the cycle is the removal of air from the devices being sterilised. The cycle presently offered on the Sterrad


100 and NX series involves pulling down to a low vacuum in the region of 300 mTorr (390 10-3


uses both a lower vacuum (typically less than 1 10-3


which allows air to be drawn out of the load (Fig. 3).


33


mbar) (Fig. 2). The CISA SPS system mbar) and a series of vacuum washes


stage sterilisation hold stage air flush


Chamber pressure mTorr


Preplasma


Vent 1


Injection 1 Diffusion 1 Plasma 1


Injection 2 Diffusion 2


Plasma 2


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