GUIDE TO AUTOCLAVING PIONEERS IN STERILIZATION TECHNOLOGY

Transcription

1 GUIDE TO AUTOCLAVING PIONEERS IN STERILIZATION TECHNOLOGY

2

3 What is Sterilization? Sterilization may be defined as the statistically complete destruction of all microorganisms including the most resistant bacteria and spores. This is a condition that is difficult to achieve and hard to prove. Whilst there are many chemicals, inorganic and organic, that kill microorganisms they may not be totally effective and can leave undesirable or toxic residues. Ultraviolet and Ionising radiations are also effective biocides, disrupting or modifying the DNA to prevent replication, but Ultraviolet will not produce the effective results and easy validation that moist heat (steam) sterilization can provide. If sterility is an absolute requirement then today s scientists turn, as their predecessors did, to steam. Microorganisms tend to become more active as the temperature of their surroundings rises, - most, but not all, die at above 80 o C. In the case of Prions the temperature and time requirements for deactivation are much higher. Steam molecules condense on cooler microorganisms, and transfer 2500 joules per gram of steam, very efficiently heating the microorganisms to the temperature at which they are destroyed. Other methods of heating suffer from the much lower heat transfer of hot dry gases and boundary layer effects, which can insulate and protect the microorganisms. For maximum effect the Steam must be saturated, and this condition, and the temperature and pressure of the steam are easily monitored, facilitating proof that sterilization has occurred. By employing Steam Sterilization techniques a high level of sterility can be achieved and the most popular piece of equipment used in laboratories and hospitals is the STEAM STERILIZER or AUTOCLAVE. How does an Autoclave work? The terms Autoclave and Sterilizer are interchangeable and mean the same thing. Autoclave is a term used mainly in laboratories whilst Sterilizer is used more commonly for medical and pharmaceutical applications. An effective Autoclave or Sterilizer must contain dry saturated steam. In order to achieve this air must be removed from both the load and the chamber; this can be accomplished in a number of ways. Air removal from high mass low load items (i.e. comprising mainly solid areas that contain little or no air pockets such as bottled media) will need little air removal and this can be facilitated by automatic air purging. Here air is allowed to leave the chamber through a vent as steam enters the chamber either from an integral source (upward displacement) or an external supply (downward displacement); this vent only closes when all of the air is removed from the chamber. This method can be further advanced by Freesteaming when the vent is allowed to stay open for a set length of time. The turbulent steam then passes through the vent forcing any trapped air out of the autoclave. For more stubborn loads that contain a number of air pockets such as wrapped instruments or fabrics, a more effective method of air removal is essential. By far the most effective way of air removal is a vacuum system, whereby a vacuum is achieved in the chamber before any introduction of steam, removing most of the air before freesteaming and/or vacuum pulsing. Once all of the air is removed from the load and chamber the temperature within the vessel will rise along with the pressure until the pre-selected temperature is reached. To achieve a typical sterilization temperature of 121 o C or more, requires the steam to be pressurized to at least 1.1 Bar G. Since pressures used are greater than 0.5 Bar G the Autoclave assembly is classified as a pressure system and must be designed to a strict engineering standard such as PED97/23EC/PD5500/ASME etc. The temperature within the chamber is reached in a number of ways: 1) Steam can be injected into the chamber via an internal steam source such as an integral stainless steel steam generator, which can be built within the Autoclave cabinet or can be supplied as a separate unit. 2) Some laboratories or hospitals have their own direct steam source, which would similarly be injected, into the chamber. 3) In some Autoclaves heaters are built into the base of the chamber and the water is heated until it boils and produces steam. The main advantage of using a steam generator (or the direct steam method) is that cycle times can be considerably faster as the steam is immediately available. In basic autoclaves the water is topped up manually by pouring water into the vessel whilst some autoclaves are connected to a direct water supply and the water level is maintained automatically. Some of Astell s smaller units are available with an integral water tank, which once filled, can run for up to 20 cycles repeatedly before being replenished. In CSSD applications it is a requirement that the steam is dry saturated steam with a known dryness and noncondensable gas content e.g. in the UK, Steam with values within the specification set out in HTM2010. When the desired temperature is achieved for the required time then the steam supply will cease either by shutting off the power to the heaters or by cutting off the steam supply. Thus the temperature and the pressure will gradually drop. In units with a vacuum system fitted the vacuum pump can be used to remove the steam (i.e where drying is required).

4 Typical Autoclave Cycles Typical temperature/time sterilization parameters are 115 o C for 30 minutes, 121 o C for 15 minutes and 134 o C for 3 minutes. However, overall cycle times will vary depending on load characteristics. Firstly it is important to realise that the time and the amount of steam that is needed for the load to reach Sterilization will vary greatly depending on the thermal capacity of the load in question. Two or Three 1 litre bottles of culture media will often need more steam than a dozen small containers, and the heating time will take longer. Likewise the time taken to achieve Sterilization once the temperature has been attained will depend on the type of microbiological organisms present. Bacteria and fungi are rapidly killed by moist heat but viruses and particular bacterial spores are very persistent, and may need long Sterilization times. The development and wide availability of reliable microprocessors means that most modern autoclaves are fully user programmable, allowing the Sterilization temperature to be set to suit the requirements of the load. The most accurate way of ensuring that Sterilization occurs when the correct temperature is reached is by Load Sensed Process Timing. Here the cycle is controlled via the temperature achieved in the centre of the load. A wandering thermocouple probe situated within the chamber is inserted into the load, or a load simulator and initiates the sterilization period once the probe reaches the programmed threshold temperature. This ensures that sterilization starts at the correct stage of the cycle. Following Sterilization and depressurization of the chamber it may be possible to open the autoclave immediately. However, when autoclaving bottled fluids, a cooling lock is normally fitted to comply with various safety regulations (e.g. in the UK: HSE PM73). This prevents the autoclave from being opened until the load temperature has fallen to typically 80 o C, thus reducing the risk of both the boiling over of fluids (e.g media) and the explosion of glass bottles. Types of Cooling Following Sterilization it is possible to have a variety of fast cooling options fitted which reduce the cool down period. Water Cooling Deluge Cooling This can often cut cycle times down by up to 50% and is used only in conjunction with sealed fluid loads. Water at Sterilization temperature is sprayed onto the load after the completion of the sterilization stage. The water being sprayed is passed through a heat exchanger cooled by cold water thus producing a controlled reduction in temperature throughout the load. This is a highly specialised method of cooling, and due to the volume of water used during the deluge stage it is only suitable for sealed bottled fluids. Water Fed Jacket A Jacket can be fitted to the autoclave chamber on both circular and square section units. Again cold water is introduced into the jacket at the end of the sterilization stage of the cycle using the chamber walls as a heat exchanger reducing temperature and resulting in improved cooling. As the jacket acts as a very efficient heat exchanger pressure reduction can be very fast using this method and therefore it is generally recommended that Air Ballast is used in conjunction with the jacket to reduce the possibility of fluid loss. Advanced Water Cooling This can only be fitted to machines that have been connected to a mains water supply. A series of cooling coils are fitted to the outside of the autoclave chamber. At the end of sterilization these coils are circulated with cold water and so results in a rapid decrease of temperature and improved cooling time. Fan Assisted/Air Cooling Assisted Air-Cooling Fans are fitted within the cabinet and circulate ambient air over the external chamber walls during the cooling stage of the cycle creating a controlled improvement to cooling times. Internal Convection Fan Assisted Cooling A fan or fans can be built within the chamber and ducted to create an efficient airflow. The fan is again activated during the cooling stage of the cycle. The fans create turbulence reducing cooling time greatly. Internal convection fan cooling is one of the most proficient ways of cooling the chamber. To ensure improved cooling time the optional jacket and/or advanced water-cooling is also needed. On loads using unsealed bottles air ballast is recommended. The importance of drying! It is important to take into account exactly what the autoclave will be used for before running a cycle. Some items such as fabrics & wrapped instruments require special attention as they will need a specific drying cycle to avoid them being left wet at the end of the cycle. The best way of ensuring that this does not happen is by having a pre and post vacuum as well as a steam heated jacket fitted to the chamber. The pre-vacuum is required to remove air from the load and the post vacuum will remove moisture left on the load. The drying will be enhanced with the addition of the steam heated jacket, which is filled with steam throughout the cycle; this heat prevents excessive condensation being formed on the chamber walls and maintains the temperature above the boiling point during drying so that water droplets boil off. The Heated jacket is essential for optimum drying performance.

5 Uses of Autoclaves Autoclaves can be used for numerous medical and laboratory applications in Market Sectors such as, Food and Dairy, Universities & Colleges, Agriculture & Horticulture Research, Healthcare (including Pathology), Industrial Research, Water & Environmental, Brewing, Biotechnology Industries and Pharmaceuticals Typical applications include: Media Preparation Sterilization of Fluids Instruments (Wrapped and Unwrapped) Utensils and Lab Equipment Fabrics and Textiles Media Preparation: Media is used to grow microorganisms under test conditions and a wide variety of gel and liquid media is used. Air removal from fluid/media loads is normally straightforward; however some media cycles can benefit from a short period of free steaming. Different types of media withstand different sterilizing temperatures, therefore any autoclave used for the Sterilization of media must be capable of sterilizing at a variety of temperatures. Cycle times must be short and the speed of processing is vital. A fast heat up and cool down is beneficial in the maintenance of the quality of the finished product and prevents the over cooking which leads to the deterioration in the quality of the growth medium. Cycle length should be set to as short as possible, and at the temperature specified by the media manufacturer. The cool down period however, needs to be a controlled process in order to prevent boil over and loss of media. The main method of controlling the sterilzation procedure of any cycle is to use a thermocouple probe in a dummy bottle within the chamber (Load Sensed Process Timing). Only when the probe reaches the correct temperature will the sterilization process begin. Load Sensed Process timing is used in conjunction with Profiled Overshoot Boost, this allows the temperature in the chamber to rise above the programmed level to allow the load to reach the correct temperature faster. The risk of any boil over can be greatly reduced by using Air Ballast which maintains chamber pressure during the cooling phase. 3000mbar 2100mbar 2000mbar 1000mbar Ombar START VAC POSITIVE PULSE STERILIZE COOLING DRYING AIR BREAK Sealed Fluids Cycle Graph Sealed Fluids: Some fluid loads may require to be sterilized in special sealed containers. Air purging is normally sufficient to remove air, and extended freesteaming should be unnecessary. As with media preparation the speed of processing is vital to the quality of the end product and often temperatures in excess of 121 o C will be used to speed up the Sterilization process. Again the cooling should be as short as possible. 3000mbar 2000mbar 1000mbar Ombar START VAC POSITIVE PULSE STERILIZE COOLING DRYING AIR BREAK Instruments: The Sterilization of instruments falls into two main categories: a) Unwrapped Instruments b) Wrapped Instruments Both types of instrument loads benefit from drying the end of the cycle. Unwrapped instruments can be dried by the heating of the surrounding air at the end of the cycle, whilst wrapped instruments require a more sophisticated drying system Post vacuum systems on small bench-top units will improve drying, whilst a jacketed pressure vessel is strongly recommended on larger units. 3000mbar 2000mbar 1000mbar Ombar Sealed Fluids Cycle Graph (including assisted cooling) START VAC NEGATIVE PULSE POSITIVE PULSE STERILIZE DRYING AIR BREAK Typical Glassware/Utensils (134ºC) Cycle Graph

6 Fabrics and Textiles: A variety of fabrics and textiles can be sterilized in an autoclave/sterilizer, e.g many hospitals will use an autoclave to sterilise gowns, instrument packs etc. As these are true porous loads they will require both pre and post vacuum systems, negative and positive steam pulsing and a fully heated jacket. Steam quality is important when operating Porous Load Autoclaves. Load Vacuum Assisted Sensed Vacuum & Assisted Cooling Process Pulsing Heated Cooling & Air Timing Jacket Ballast 3000mbar VAC NEGATIVE PULSE POSITIVE PULSE STERILIZE DRYING AIR BREAK Media x x ( 3) 2000mbar 1000mbar Ombar START Mixed Discard x x x Typical Fabrics Cycle Graph Discard Loads: There is an ever-increasing need for the safe Sterilization of contaminated material before disposal to ensure that it is microbiologically safe. The contaminated material can be of many types and in many forms. For example, all microbiological laboratory waste should be processed prior to disposal, as must all clinical samples e.g. blood, tissue etc. Loads consisting of such a wide variety of materials in a broad range of containers will present specific Sterilization problems. One of the main problems with such mixed discard loads is that they invariably contain small pockets of trapped air, which present particular air removal problems before steam penetration. Such loads are often contained in special plastic bags and comprise a variety of plastic containers; these are liable to melt and collapse before Sterilization, thus increasing the likelihood of trapped air. A pre-vacuum and steam pulsing feature is now a commonly requested option for autoclaves running frequent discard cycles. However an alternative to vacuum is a long period of freesteaming or Pulsed Freesteaming PAT. There are special discard (Morrison) containers available for this application. In certain circumstances a doubledoored autoclave may be required. The loading ( dirty or nonsterile) end is often separated from the unloading ( clean or sterile) end by a wall, which often contains an SPF seal to prevent bacteriological migration. In category III laboratories an effluent retention system would also be necessary. Fluid Discard Glassware Unwrapped Instruments Wrapped Instruments x x x x x x x ( 1) x x x ( 1) x x 3000mbar VAC POSITIVE PULSE STERILIZE DRYING AIR BREAK COOLING 2000mbar Fabrics x ( 2) x x 1000mbar Ombar START Typical Fluid Discard Cycle Graph Essential Recommended x Not Needed (1) If dry load is required (2) Vacuum & Heated Jacket required to ensure drying of Fabric Loads (3) To prevent excessive cycle time

7 Monitoring the Sterilization process Verification has become increasingly important, as there is often a need to trace back through a series of results to ensure that a particular Sterilzation process has been carried out. There are a variety of options that are available for this; these can either be mounted externally i.e on an adjacent wall or shelf, or can be an integral part of the autoclave. Printers, Chart Recorders or Dataloggers are the preferred options. These instruments can provide either a hard copy record of exactly what the microprocessor is registering, or they can be completely independent from the microprocessor and record independent results of chamber and load conditions. Data Printers Integral Data Printer Built as an integral part of an autoclave this is the most popular and cost effective way of monitoring the cycle. When the cycle begins the printer records the starting time, cycle number, program number (or name) and machine type. The printer will print a complete record of cycle conditions, freesteam, sterilizing start and finish time and pressure readings at one-minute intervals. There is also provision for operator signature and batch number. Secureprint Data Printer This is a Freestanding Data- Printer independent of the microprocessor, which is designed to give an independent printer verification of the sterilizing function. Chamber temperature, pressure, load and time is displayed and printed with a dual speed papersave feature. (This printer will also operate with any non Astell Autoclave) Chart recorders Chart recorders are the traditional method of printing the Sterilization process. These show a graphical display of pressure and/or temperature come with either one, two or three pens, single pen recorders register chamber temperature, two pen recorders register chamber temperature and load temperature and the three pen recorders register chamber temperature and load temperature via two wandering probes, options also include measurement and display of pressure. The recorders can either come in strip or circular format. Circular Chart Recorders These are high performance microprocessor based recorders with an alphanumeric display to provide more information and easier operation. The recorders are available with up to 1, 2 or 3 pens. Reading accuracy is 1% of Span of the instrument. The programme system allows full control of ranging, plus control of the pen drive, lift and referencing, and display. The tactile membrane switches are mounted at the front, alongside the display, behind the door for security. Strip Chart Recorders These are microprocessor controlled strip chart recorders available with 1,2 or 3 coloured pens. Recording accuracy is 1% of span through the use of accurate stepper motors. The recorder incorporates a high definition alphanumeric display, indicating temperatures and pressure. Astell AutoSCRIBE Datalogger Typical printout from integral or Secureprint data printer. The Astell datalogger is a purpose designed, wall mounted datalogger with LCD display and keyboard. The datalogger is specially configured to record temperature and time parameters. The configuration of the AutoSCRIBE allows maximum storage by only recording during the operation cycle. The data is downloaded on demand to a laboratory P.C. for analysis and archiving.

8 Installation The satisfactory performance of any Autoclave requires that it is installed in accordance with the instructions supplied by the manufacturer. Some small benchtop autoclaves require little or no installation as they have an integral recirculation water tank; therefore the machine requires no plumbing to a mains water supply or drain. Where connection is required to the various services (i.e water, drain, power etc) Astell supplies full installation instructions and diagrams; an example of which is shown. (2) (4) 1) Machine Power Switch 2) Power Supply= Switched FUSED connection unit 3) Chamber Exhaust carrying steam & condensate 4) Vent to external atmosphere or extraction hood 5) Connection to Drain- 35mm Copper. Must be connected to drain with sealed plumbing connection no gaps for steam to escape 6) Building Drain This must flow freely under gravity away from machine;-minimum diameter 50mm. At no point must this slope uphill and there must be no dead legs, loops or u-bends. Between machine and the main drain system. 7) Chamber Drain for cleaning only. May be plumbed to Building drain if required. (3) (5) (1) (6) (7) Typical installation (Electrically heated model) Validation It has become increasingly important to comply with Quality Assurance procedures, which require validation that Sterilization has been achieved. Validation is best defined as the documented procedure of obtaining, recording and interpreting results to ensure that the machine will consistently carry out a defined process. This will involve carrying out multi-point temperature mapping to establish suitable loading configurations and cycle parameters to ensure that the process is controlled within predetermined limits. Astell Scientific is a UKAS accredited company. For further details contact our Service Department. TEMPERATURE/PRESSURE CORRELATION The table below shows Pressure and Temperature correlation for Saturated Steam, and the Maximum/Minimum acceptable Temperature display Values for a Correlation Accuracy of +/- 2%. It applies to ASTELL Sterilizers only. Pressure Temperature Temperature - Tolerance Bar Deg C Min Temp Max temp

9 Astell - Pioneers in Sterilization Technology Astell Scientific have been pioneers in the manufacture and validation of Scientific and Laboratory equipment for over 80 years. In the last decade the company has concentrated on becoming market leaders in Sterilization technology and is now one of the premier manufacturers in this field in Europe. A wide range of standard front and top loading microprocessor controlled Autoclaves are offered including circular section units from Litres and Square Section Sterilizers from litres. In recent years Astell has successfully developed its bespoke manufacturing facility and offers a wide range of non standard units in capacities up to 1000 litres. All of the units feature the secure micro-computer controller, which is user friendly and fully programmable. A variety of options and accessories can be supplied with all models to ensure optimum performance and user flexibility in the most demanding situations. These range from Data Printers, Load Sensed Process timing and a variety of cooling options to reduce cycle time. The Astell range can be catogorised as follows: NB. For further information on Astell s Autoclaves and Sterilizers please refer to our separate brochure: The Autoclave Range or visit our Website at Swiftlock Compact Autoclaves, 23, 40 & 60 Litres This range of circular section autoclaves from Astell offer guaranteed precision and versatility for a wide range of applications. Featuring many of the benefits associated with Astell s larger units these stylish yet economical models meet the demanding requirements of current Sterilization procedures. These are now available in the Classic and Autofill versions. Secure micro-computer control 316L stainless steel pressure vessels Temperature range C ( Bar) Super-quick New Swiftlock door mechanism Compact ergonomic designs Automatic cycle control Built in drying system (Autofill version) Integral reservoir and/or condensate bottle 10 Year Pressure Vessel Integrity Warranty Media holdwarm feature (Classic version)

10 Autoclaves, Swiftlock, 90 to 330 Litres A range of top loading and front loading microprocessor controlled autoclaves in volumes from 90 to 330 Litres. The easy open/close Swiftlock closure combines with a user-friendly control system to ensure simple operation for all applications, whilst a comprehensive range of safety features ensures peace of mind for the user. Cost Effective Full Heated Jacket Available for Optimum Drying Secure Microcomputer control PIN restricted user programming Single action closure Holdwarm for Media Preparation Timed freesteaming 316L Stainless Steel Vessels Cooling locks for the safe Sterilization of liquids Single or multi-program models available Temperature Range o C ( Bar) Optional Vacuum/AirBallast. 10 Year Pressure Vessel Integrity Warranty Autoclaves, Square Section (including models with Vacuum & Air Ballast) A comprehensive range of Square and Rectangular Section front-loading autoclaves, in standard volumes from 100 to 490 litres Maximum Space Utilisation Easy Loading PIN restricted user programming Fully interlocked sliding door. 316L Stainless Steel Vessels Temperature range o C ( Bar) Standard sectional jacket with water cooling. Optional Vacuum & Air Ballast Double door units available 10 Year Pressure Vessel Integrity Warranty The modular internal chamber dimensions of these units ensure maximum space utilisation for all Sterilization purposes. The models with vacuum facility are especially suitable for difficult discard loads, ensuring efficient air removal prior to Sterilization. All units now feature the New LogiColor Colour Touch Screen Controller. For further information on Astell s Autoclaves and Sterilizers please refer to our separate brochure: The Autoclave Range or visit our Website at Continuing efforts to improve products may necessitate alterations to specifications without notice.

11

12 Astell Scientific Limited, Powerscroft Road, Sidcup, Kent DA14 5DT United Kingdom T +44 (0) F +44 (0) E [email protected] Direct Sales: T +44 (0) /3/2 F +44 (0) Certificate No: Q536