GB2367494A

GB2367494A - Sterilizing enclosures using sterilant vapours

Info

Publication number: GB2367494A
Application number: GB0019215A
Authority: GB
Inventors: James Lindsay Drinkwater
Original assignee: MICROFLOW Ltd; Bioquell UK Ltd
Current assignee: MICROFLOW Ltd; Bioquell UK Ltd
Priority date: 2000-08-04
Filing date: 2000-08-04
Publication date: 2002-04-10
Also published as: GB0019215D0; WO2002011774A1; AU2001275743A1

Abstract

A method of sterilising a sealable enclosure comprising the steps of initially adjusting the relative humidity in the enclosure to a level substantially below ambient, circulating a carrier gas to the enclosure at a temperature raised above ambient at a first flow rate, supplying a sterilant vapour or vapours to the circulating carrier gas sufficient to saturate substantially the gas whereby, on cooling in the enclosure, a condensate of the sterilant vapour is formed on surfaces in the enclosure. Circulation of the gas/vapour is continued for a sufficient period of time to ensure sterilisation of the enclosure and any contents of the enclosure by the condensate which has been formed. Supply of sterilant vapour to the circulating gas is then terminated and circulation of the gas is continued at a second much higher flow rate, whilst removing sterilant vapour from the circulating gas to remove the sterilant from the enclosure. The sterilant may be hydrogen peroxide vapour.

Description

2367494 Decontamination of Recirculating Flo The invention relates to a

method for the rapid removal of a sterilising gas from an isolator. 5 In most gaseous sterilisation processes the longest part of the cycle is the removal of the active gas after the sterilisation has been achieved. All of the gases used for sterilisation are harmful to man 10 and must therefore be reduced to a safe concentration before access is gained to the sterilised zone.

A further consideration is the damage that may be caused to products by exposure to low concentrations is of sterilising gas.

It is therefore important that such gases are removed, but the removal to low concentrations is normally only achieved by flushing the chamber with a 20 large amount of fresh air. The problem of the removal of the sterilising gas is made more difficult by the absorption of the gas into the surface of the chamber. The absorbed gas must then be removed and diluted to achieve a safe level before any processing is 25 recommenced. The removal of the gas may take place in a number of ways. It may be decomposed in a catalytic system attached to the sterilising gas generator, or it may be expelled to the outside.

30 Expelling high concentrations of harmful and polluting gases to the environment is becoming a less acceptable solution. Decomposing the gas in the generator will take a considerable time because the airflow rates are those required to generate the gas, 35 and these are quite small.

This invention provides a method of sterilising a sealable enclosure comprising the steps of initially adjusting the relative humidity in the enclosure to a level substantially below ambient, circulating a carrier gas to the enclosure at a temperature raised above 5 ambient at a first flow rate, supplying a sterilant vapour or vapours to the circulating carrier gas sufficient to saturate substantially the gas whereby, on cooling in the enclosure, a condensate of the sterilant vapour is formed on surfaces in the enclosure, 10 continuing to circulate the gas/vapour for a sufficient period of time to ensure sterilisation of the enclosure and any content has been achieved as a result of the condensate that has formed, terminating supply of sterilant vapour to the circulating gas and finally 15 circulating the gas at a second much higher flow rate and removing said sterilant vapour from the circulating gas to remove the sterilant from the enclosure.

The solution to this problem is to use the very 20 high airflow rates available within the isolator. if this very high circulating airflow within the isolator is passed through a device to remove the active gas then clean air could be returned to the isolator, thus quickly removing the active gas from the chamber.

The most common of the sterilising gases in the pharmaceutical industry is hydrogen peroxide, because of the speed at which it kills microorganisms, and that it does not leave any residues. Certain forms of catalytic 30 carbon may decompose hydrogen peroxide gas and it is therefore possible to manufacture a device to remove the hydrogen peroxide gas from the very high circulating airflow using a catalytic carbon filter.

35 In the case where the sterilant vapour or vapours comprise hydrogen peroxide vapour and water vapour, both hydrogen peroxide and water vapours may be removed from -3the carrier gas in said final circulating of the gas.

In the above method the final rate of circulation of the carrier gas is some 40 times the first rate of 5 circulation of the gas.

In the above method, there may be one f low path for the circulation of gas at said first rate and a second flow path for circulation at the second rate.

More specifically the second flow path may include a catalytic convertor to break down hydrogen peroxide into water vapour and oxygen and a fan for carrying the carrier gas to flow through said second path.

The following is a description of a specific embodiment of the invention, reference being made to the diagrammatic drawing of an isolator and decontamination circuit.

The diagram shows the main components of a simple laminar flow isolator system. The Isolator (1) is fitted with an Inlet Filter (2), which will cover the whole of one face of the chamber, normally the top, to 25 generate vertical laminar down-flow. In an ideal situation the opposite face of the isolator will also be the Exhaust Filter (3) in order to maintain as near as possible laminar flow. For practical reasons it is not normally possible to make the whole of the base area of 30 an isolator the exhaust filter so other suitable arrangements are made to extract the air near the base, and in some special cases in another face of the isolator, i.e. not the base. The air is circulated through the isolator (1) by a Fan (4). The normal 35 circulating airflow generated by Fan (4) would be sufficient to give a laminar airflow velocity inside the chamber about 0.3m/s. Typically the air path through a chamber will be about 900mm giving a passage time of the air through the isolator of 3 seconds or 20 air changes per minute or 1200 air changes per hour.

5 To remove any gaseous contamination that may build up inside the chamber, or to maintain a stable temperature it is normal practice to introduce some fresh air into the circulating air stream. Introducing air through a make-up filter (8), the air being supplied 10 by the make-up fan (9), will do this. While the make-up air is being provided to the chamber the three-way valve will be connected through parts D to F.

In order to maintain the correct pressure balance 15 inside the isolator a similar moon of air to that added by the make-up fan (9) must be extracted and this is removed through the extract filter (6) and the extract fan (7). To make the extraction of air possible ports A and C are connected at the three-way valve (10). The 20 make-up Fan (9) and Extract Fan (7) therefore maintain the flow of fresh air to the isolator and also the required pressure balance.

When it is required to sterilise the surfaces 25 inside the isolator (1) the position of the three-way valve (11) is adjusted to give the flow path through paths E and F. A similar change is made to the three way valve (10) giving a flow path through B and A. The sterilising gas may then be introduced into the chamber 30 through the entry port (12) and extracted at port (13).

Some recent developments in surface sterilisation technology have shown faster deactivation of surface contamination by injecting the sterilising gas directly 35 into the chamber. This requires that the sterilant is delivered into the chamber and distributed within the chamber before it cools.

Following sterilisation it is necessary to remove the active gas. This would normally be performed either by passing the air through the gas generator which will decompose the active gas or supply fresh air through the 5 make-up fan (9). Both of these systems have a limited flow rate causing the time to remove the active gas to be extended.

The present device uses the circulatory fan (4) to 10 circulate the air through the Isolator (1). A catalytic carbon filter (5) is placed in the circulating airflow down stream of the exhaust filter (3). This catalytic carbon filter decomposes the' active gas in the circulating airflow thus returning clean air to the is isolator through the inlet filter (2). As explained earlier the re- circulating airflow will change the air in the isolator (1) in excess of 1000 times per hour, considerably faster than the fresh make-up air or the air supplied from the gas generator.

The greater increased flow of clean air dramatically reduces the time to reduce the active gas concentration in the isolator (1) to a safe level, returning it to use in a much shorter time.

Claims

1. A method of sterilising a sealable enclosure comprising the steps of initially adjusting the relative humidity in the enclosure to a level substantially below 5 ambient, circulating a carrier gas to the enclosure at a temperature raised above ambient at a first flow rate, supplying a sterilant vapour or vapours to the circulating carrier gas sufficient to saturate substantially the gas whereby, on cooling in the 10 enclosure, a condensate of the sterilant vapour is formed on surfaces in the enclosure, continuing to circulate the gas/vapour for a sufficient period of time to ensure sterilisation of the enclosure and any contents of condensate has been formed, terminating 15 supply of sterilant vapour to the circulating gas and finally circulating the gas at a second much higher flow rate and removing said sterilant vapour from the circulating gas to remove the sterilant from the enclosure.

2. A method as claimed in claim 1 or claim 2, wherein the sterilant vapour or vapours comprise hydrogen peroxide vapour and water vapour and both hydrogen peroxide and water vapours are removed from the carrier 25 gas in said final circulating of the gas.

3. A method as claimed in claim 1 or claim 2, wherein the second rate of circulation of the carrier gas is substantially greater than (e.g. 40 times) the first 30 rate of circulation of the gas.

4. A method as claimed in any of the preceding claims, wherein there is one flow path for the circulation of gas at said first rate and a second flow path for 35 circulation at the second rate.

5. A method as claimed in claim 4, wherein the second flow path includes a catalytic convector to break down hydrogen peroxide into water vapour and oxygen and a fan 40 for carrying the carrier gas to flow through said second path.