On This Page On This Page 10-Step Guide to Autoclave Temperature and Pressure Written by: Bill Warren In labs and sterile processing departments, autoclaves play an important role in ensuring that equipment and instruments are free of contaminants that can compromise experiments, research, or patient safety. But how do these machines guarantee sterility? The answer lies in their use of temperature and pressure to create the kinds of environments that are lethal to harmful microorganisms. Read on to discover more about how autoclave sterilization works, the role of essential elements, and much more. How Autoclave Sterilization Works No matter the setting or application an autoclave is used for, most models rely on a combination of temperature, pressure, steam, and time to achieve sterilization. Each of these elements play a crucial role in the process, serving the following purposes: Temperature — In a steam sterilization cycle, the temperature within the autoclave chamber is raised to a degree in which contaminants (such as bacteria, viruses, fungi, and spores) are unable to survive. Pressure — Steam is an Ideal Gas, for which pressure and temperature are predictably related. Steam at a given temperature will always exert a predictable pressure. Autoclave sterilizers must be designed to withstand these pressures, and sensing equipment that reads pressure can be used to verify that steam within the chamber is still behaving correctly. Steam — During the sterilization process, steam acts as a conduit that transfers heat to microorganisms, ultimately destroying them. Steam is a much more efficient medium for transferring heat than air, which is why it is frequently used in autoclaving cycles. Time — It takes varying amounts of time to achieve sterilization. The rate at which contaminants are destroyed is expressed as time at a given stable sterilization temperature. How long a cycle lasts depends on the load type and desired Sterility Assurance Level. Though the process of achieving sterilization remains consistent across the majority of autoclaves, there are a variety of different model types that are used for different purposes, depending on the setting. Some of the most common are: Gravity displacement autoclaves — These are primarily used for processing laboratory media, water, pharmaceutical products, regulated medical waste, and nonporous articles whose surfaces have direct steam contact. High-speed pre-vacuum sterilizers — Ideal for wrapped goods (such as surgical packs), pipette tips and other high-density polyethylene products (e.g. syringes), media solutions in containers (tissue culture flasks), and medical textile items (such as textile-based personal protection equipment). Table-top steam sterilizers — These models are mostly used in outpatient, dental, and rural clinics and are designed for small instruments, such as hypodermic syringes, needles, and dental instruments. Bulk sterilizers — Large, room-scale sterilizers are employed mainly at central sterile departments and other high-throughput settings. They are typically constructed into a building, such that the floor of the autoclave chamber is level with the floor of the building, allowing sterile technicians to load goods into the autoclave on rolling racks. It’s important to note that autoclave manufacturers establish temperature and pressure settings, so that each unit arrives with predefined, validated cycles. This way, you don’t have to set the temperature and pressure for each cycle you run. Still, it’s useful to understand the role that these elements play in the sterilization process. Optimizing Temperature for Steam Sterilization While the temperature within the chamber needs to reach a certain threshold in order to effectively sterilize a load, exact temperature requirements will vary depending on different considerations — namely load type and cycle length. For example, some items — such as thermoplastics, sensitive liquids, and some medical devices — can’t withstand higher heat and must be sterilized at lower temperatures for longer periods of time to maintain integrity of the product. Common temperature ranges for steam sterilization include the following: True low-temperature cycles are typically run between 158°F–212°F (70°C–100°C) and are most appropriate for non heat-stable objects or materials that easily congeal or shouldn’t be exposed to temperatures that are higher than atmospheric steam. As these cycles are less effective at eliminating the total microbial burden of a given load, they are not used in healthcare settings. Instead, low-temperature cycles are ideal for purposes where the aim is reduction of the microbial burden. 250°F (121°C) is a common sterilization temperature for wrapped goods where the higher heat of pre-vacuum treatment is unviable. Cycles at this temperature take significantly longer than cycles at higher temperatures, but the tradeoff may be advisable for more heat-sensitive goods. 270°F (132°C) is typically used for shorter, immediate-use cycles when a single item is urgently needed for a procedure and time for steam to penetrate an entire load is not a concern. A temperature of 275°F (135°C) is reserved for pre-vacuum sterilization of durable items — such as wrapped goods, packs, cages, and porous materials — that can withstand greater temperatures. With any cycle, it’s important to keep in mind that temperature has a direct impact on sterilization outcomes. If the temperature is too low, achieving full sterilization may take an extremely long time. Conversely, if the temperature is too high, you risk damage to the items in a load. The relationship between sterilization temperature and time is exponential, with slight changes in temperature having major impacts on time. The Role of Pressure in Autoclave Sterilization As previously mentioned, high temperature alone is not enough to achieve sterilization — pressure must also be present. This is for several reasons. Primarily, as steam follows the Ideal Gas Law, pressure predictably raises the temperature of the steam within the chamber to reach a degree that’s optimal for killing harmful microorganisms. The addition of pressure also makes it possible for liquids to undergo sterilization without boiling. This is because when pressure is raised, so is the liquid’s boiling point, if only temporarily. For example, liquid water can be sterilized at 250°F (121°C), 38°F (21°C) over its normal boiling point as a result of the pressure within the chamber during the sterilization cycle. By slowly reducing the pressure as the liquid cools, it can then be safely removed from the chamber after sterilization. Pressure also has a direct impact on sterilization effectiveness… If the pressure is too high, loads can become damaged, steam can escape or become superheated, and temperatures can become too elevated. If the pressure is too low, the cycle may take too long for loads to achieve sterility, steam may not sufficiently penetrate the load, and temperature may be too low to effectively remove all harmful contaminants. Though these are risks to be aware of, many modern autoclaves have precise pressure controls that ensure the proper pressure is achieved and maintained during sterilization cycles. Additionally, some autoclaves are also equipped with vacuum systems, which enable the unit to apply negative pressure to goods before and after sterilization, aiding in the removal of air and moisture from porous goods. Overcoming Autoclave Temperature & Pressure Challenges Maintaining ideal temperature and pressure isn’t without challenges. For example, occasionally, an autoclave may not fully pressurize. This could be for a couple reasons: Perhaps problems with the water supply or heating element inhibit the unit’s ability to reach its pressure setpoints, or bellows and door gasket issues could be allowing pressure to escape the chamber. Similarly, an autoclave may struggle to reach temperature. In this case, check the steam generator to ensure it’s powered on or to inspect any potential damage. If the steam generator is in working order, look to see if the chamber drain is clogged, whether there’s a problem with the steam trap, or a malfunctioning valve. If any of the fixes to these issues involve major repairs, it’s always best to call in a professional to address the problem. 10 Tips for Maximizing Autoclave Performance So how can you ensure you’re getting the most value out of your autoclaves’ performance? These 10 tips are a good place to start: Follow loading best practices, such as allowing for ample room between items, placing empty containers upside down, and being sure not to overload the autoclave. Set up a regular service schedule for your autoclave lineup. Email [email protected] to get in touch with your local service group. When ordering your autoclave, ensure that it’s equipped with the best loading options for the goods you plan to sterilize. Use packaging that allows for full steam penetration and holds up to the temperature of sterilization. Always allow the cooling phase to fully complete before opening the chamber. This is especially critical for liquid loads. Monitor and save cycle records to watch out for any changes in autoclave performance. Validate your existing autoclave lineup using biological indicator tests to ensure a given cycle and load will achieve sterility. Then, document those cycles in a standard operating procedure for consistent results. Validate any newly purchased autoclaves after installation using qualification tests. Regularly run test cycles such as Bowie Dick and Vacuum Leak tests. Ensure that your autoclaves’ steam generator and valves are not being taxed and reduce water bills by engaging standard sustainability features. Autoclave Safety Protocols As autoclaves operate at high temperatures and pressures, they can pose significant risks to user safety. To protect technicians from harm, strict safety practices related to the autoclave should always be in place and followed carefully. At the very least, safety measures should include the following: Personal protective equipment should be worn on eyes and hands at all times while loading and unloading an autoclave. It’s crucial to remember that jacketed autoclaves preheat prior to a cycle being run, so the walls and door of the autoclave will already be at a temperature hot enough to cause contact burns on bare skin, even while loading. Always check the chamber pressure gauge on the front of the autoclave prior to attempting to open the door. Even a small amount of pressure inside the chamber could cause the door to open at force. Materials such as polystyrene, polyethylene, bleach, hypochlorite, and other corrosive chemicals can melt or create hazardous gasses if exposed to the temperatures of steam sterilization. If you would not heat a material past the melting point of water using a bunsen burner, you should not run the material through a sterilization cycle. The pressure inside the autoclave will temporarily raise the boiling point of liquids during a cycle. If a proper liquid cycle (which has a slow pressure ramp-down to allow for cooling) is not run, liquids may boil over or glassware containing liquids may explode when exposed to cooler temperatures following a sterilization cycle. If water pools underneath the autoclave or steam exits the unit while the door is closed or no cycle is running, safety mechanisms may be preventing an unsafe buildup of excess pressure. Immediately engage safety stops and mark the machine as unsafe to use until qualified service personnel can diagnose and address the problem. Keep Your Autoclaves Running at Peak Performance Whether it’s issues related to temperature, pressure, or something else entirely, it’s crucial to avoid running into the problems that can take your autoclaves offline and sideline your facility’s operations. Routine maintenance is essential to ensure that your steam sterilizers continue to function properly for years to come. Download your free copy of our eBook: How to Properly Maintain Your Autoclave for everything you need to know about keeping your autoclaves in top shape. Have questions? Our team of sterilization experts is here to help. Contact CSS today to get the answers you need. 17 Questions to Ask Before Buying Your Next Autoclave We created this 17-question eBook as a framework to help you explore and discover the exact type of autoclave best suited to your needs. Get eBook Tweet Like Share
10-Step Guide to Autoclave Temperature and Pressure Written by: Bill Warren In labs and sterile processing departments, autoclaves play an important role in ensuring that equipment and instruments are free of contaminants that can compromise experiments, research, or patient safety. But how do these machines guarantee sterility? The answer lies in their use of temperature and pressure to create the kinds of environments that are lethal to harmful microorganisms. Read on to discover more about how autoclave sterilization works, the role of essential elements, and much more. How Autoclave Sterilization Works No matter the setting or application an autoclave is used for, most models rely on a combination of temperature, pressure, steam, and time to achieve sterilization. Each of these elements play a crucial role in the process, serving the following purposes: Temperature — In a steam sterilization cycle, the temperature within the autoclave chamber is raised to a degree in which contaminants (such as bacteria, viruses, fungi, and spores) are unable to survive. Pressure — Steam is an Ideal Gas, for which pressure and temperature are predictably related. Steam at a given temperature will always exert a predictable pressure. Autoclave sterilizers must be designed to withstand these pressures, and sensing equipment that reads pressure can be used to verify that steam within the chamber is still behaving correctly. Steam — During the sterilization process, steam acts as a conduit that transfers heat to microorganisms, ultimately destroying them. Steam is a much more efficient medium for transferring heat than air, which is why it is frequently used in autoclaving cycles. Time — It takes varying amounts of time to achieve sterilization. The rate at which contaminants are destroyed is expressed as time at a given stable sterilization temperature. How long a cycle lasts depends on the load type and desired Sterility Assurance Level. Though the process of achieving sterilization remains consistent across the majority of autoclaves, there are a variety of different model types that are used for different purposes, depending on the setting. Some of the most common are: Gravity displacement autoclaves — These are primarily used for processing laboratory media, water, pharmaceutical products, regulated medical waste, and nonporous articles whose surfaces have direct steam contact. High-speed pre-vacuum sterilizers — Ideal for wrapped goods (such as surgical packs), pipette tips and other high-density polyethylene products (e.g. syringes), media solutions in containers (tissue culture flasks), and medical textile items (such as textile-based personal protection equipment). Table-top steam sterilizers — These models are mostly used in outpatient, dental, and rural clinics and are designed for small instruments, such as hypodermic syringes, needles, and dental instruments. Bulk sterilizers — Large, room-scale sterilizers are employed mainly at central sterile departments and other high-throughput settings. They are typically constructed into a building, such that the floor of the autoclave chamber is level with the floor of the building, allowing sterile technicians to load goods into the autoclave on rolling racks. It’s important to note that autoclave manufacturers establish temperature and pressure settings, so that each unit arrives with predefined, validated cycles. This way, you don’t have to set the temperature and pressure for each cycle you run. Still, it’s useful to understand the role that these elements play in the sterilization process. Optimizing Temperature for Steam Sterilization While the temperature within the chamber needs to reach a certain threshold in order to effectively sterilize a load, exact temperature requirements will vary depending on different considerations — namely load type and cycle length. For example, some items — such as thermoplastics, sensitive liquids, and some medical devices — can’t withstand higher heat and must be sterilized at lower temperatures for longer periods of time to maintain integrity of the product. Common temperature ranges for steam sterilization include the following: True low-temperature cycles are typically run between 158°F–212°F (70°C–100°C) and are most appropriate for non heat-stable objects or materials that easily congeal or shouldn’t be exposed to temperatures that are higher than atmospheric steam. As these cycles are less effective at eliminating the total microbial burden of a given load, they are not used in healthcare settings. Instead, low-temperature cycles are ideal for purposes where the aim is reduction of the microbial burden. 250°F (121°C) is a common sterilization temperature for wrapped goods where the higher heat of pre-vacuum treatment is unviable. Cycles at this temperature take significantly longer than cycles at higher temperatures, but the tradeoff may be advisable for more heat-sensitive goods. 270°F (132°C) is typically used for shorter, immediate-use cycles when a single item is urgently needed for a procedure and time for steam to penetrate an entire load is not a concern. A temperature of 275°F (135°C) is reserved for pre-vacuum sterilization of durable items — such as wrapped goods, packs, cages, and porous materials — that can withstand greater temperatures. With any cycle, it’s important to keep in mind that temperature has a direct impact on sterilization outcomes. If the temperature is too low, achieving full sterilization may take an extremely long time. Conversely, if the temperature is too high, you risk damage to the items in a load. The relationship between sterilization temperature and time is exponential, with slight changes in temperature having major impacts on time. The Role of Pressure in Autoclave Sterilization As previously mentioned, high temperature alone is not enough to achieve sterilization — pressure must also be present. This is for several reasons. Primarily, as steam follows the Ideal Gas Law, pressure predictably raises the temperature of the steam within the chamber to reach a degree that’s optimal for killing harmful microorganisms. The addition of pressure also makes it possible for liquids to undergo sterilization without boiling. This is because when pressure is raised, so is the liquid’s boiling point, if only temporarily. For example, liquid water can be sterilized at 250°F (121°C), 38°F (21°C) over its normal boiling point as a result of the pressure within the chamber during the sterilization cycle. By slowly reducing the pressure as the liquid cools, it can then be safely removed from the chamber after sterilization. Pressure also has a direct impact on sterilization effectiveness… If the pressure is too high, loads can become damaged, steam can escape or become superheated, and temperatures can become too elevated. If the pressure is too low, the cycle may take too long for loads to achieve sterility, steam may not sufficiently penetrate the load, and temperature may be too low to effectively remove all harmful contaminants. Though these are risks to be aware of, many modern autoclaves have precise pressure controls that ensure the proper pressure is achieved and maintained during sterilization cycles. Additionally, some autoclaves are also equipped with vacuum systems, which enable the unit to apply negative pressure to goods before and after sterilization, aiding in the removal of air and moisture from porous goods. Overcoming Autoclave Temperature & Pressure Challenges Maintaining ideal temperature and pressure isn’t without challenges. For example, occasionally, an autoclave may not fully pressurize. This could be for a couple reasons: Perhaps problems with the water supply or heating element inhibit the unit’s ability to reach its pressure setpoints, or bellows and door gasket issues could be allowing pressure to escape the chamber. Similarly, an autoclave may struggle to reach temperature. In this case, check the steam generator to ensure it’s powered on or to inspect any potential damage. If the steam generator is in working order, look to see if the chamber drain is clogged, whether there’s a problem with the steam trap, or a malfunctioning valve. If any of the fixes to these issues involve major repairs, it’s always best to call in a professional to address the problem. 10 Tips for Maximizing Autoclave Performance So how can you ensure you’re getting the most value out of your autoclaves’ performance? These 10 tips are a good place to start: Follow loading best practices, such as allowing for ample room between items, placing empty containers upside down, and being sure not to overload the autoclave. Set up a regular service schedule for your autoclave lineup. Email [email protected] to get in touch with your local service group. When ordering your autoclave, ensure that it’s equipped with the best loading options for the goods you plan to sterilize. Use packaging that allows for full steam penetration and holds up to the temperature of sterilization. Always allow the cooling phase to fully complete before opening the chamber. This is especially critical for liquid loads. Monitor and save cycle records to watch out for any changes in autoclave performance. Validate your existing autoclave lineup using biological indicator tests to ensure a given cycle and load will achieve sterility. Then, document those cycles in a standard operating procedure for consistent results. Validate any newly purchased autoclaves after installation using qualification tests. Regularly run test cycles such as Bowie Dick and Vacuum Leak tests. Ensure that your autoclaves’ steam generator and valves are not being taxed and reduce water bills by engaging standard sustainability features. Autoclave Safety Protocols As autoclaves operate at high temperatures and pressures, they can pose significant risks to user safety. To protect technicians from harm, strict safety practices related to the autoclave should always be in place and followed carefully. At the very least, safety measures should include the following: Personal protective equipment should be worn on eyes and hands at all times while loading and unloading an autoclave. It’s crucial to remember that jacketed autoclaves preheat prior to a cycle being run, so the walls and door of the autoclave will already be at a temperature hot enough to cause contact burns on bare skin, even while loading. Always check the chamber pressure gauge on the front of the autoclave prior to attempting to open the door. Even a small amount of pressure inside the chamber could cause the door to open at force. Materials such as polystyrene, polyethylene, bleach, hypochlorite, and other corrosive chemicals can melt or create hazardous gasses if exposed to the temperatures of steam sterilization. If you would not heat a material past the melting point of water using a bunsen burner, you should not run the material through a sterilization cycle. The pressure inside the autoclave will temporarily raise the boiling point of liquids during a cycle. If a proper liquid cycle (which has a slow pressure ramp-down to allow for cooling) is not run, liquids may boil over or glassware containing liquids may explode when exposed to cooler temperatures following a sterilization cycle. If water pools underneath the autoclave or steam exits the unit while the door is closed or no cycle is running, safety mechanisms may be preventing an unsafe buildup of excess pressure. Immediately engage safety stops and mark the machine as unsafe to use until qualified service personnel can diagnose and address the problem. Keep Your Autoclaves Running at Peak Performance Whether it’s issues related to temperature, pressure, or something else entirely, it’s crucial to avoid running into the problems that can take your autoclaves offline and sideline your facility’s operations. Routine maintenance is essential to ensure that your steam sterilizers continue to function properly for years to come. Download your free copy of our eBook: How to Properly Maintain Your Autoclave for everything you need to know about keeping your autoclaves in top shape. Have questions? Our team of sterilization experts is here to help. Contact CSS today to get the answers you need. 17 Questions to Ask Before Buying Your Next Autoclave We created this 17-question eBook as a framework to help you explore and discover the exact type of autoclave best suited to your needs. Get eBook Tweet Like Share
9.30.24 Horizontal vs. Vertical Autoclaves: 6 Key Differences and Benefits → If you’re looking for a new autoclave for your facility, chances are you’ve considered several options during your search for the right one. When it comes to the question of whether a vertical or horizontal autoclave is the right fit for your lab or medical facility, understanding their key differences is crucial. To help you […]
9.26.24 Autoclave Pricing & Industry Averages → Whether you’re replacing outdated or broken units in your sterilizer lineup, expanding your sterile processing department (SPD), or opening up a brand new healthcare facility, there’s a lot to consider when selecting the right autoclaves for the job. While specs like chamber capacity, overall size, and performance are all important, price is more often than […]
9.25.24 10-Step Guide to Autoclave Temperature and Pressure → In labs and sterile processing departments, autoclaves play an important role in ensuring that equipment and instruments are free of contaminants that can compromise experiments, research, or patient safety. But how do these machines guarantee sterility? The answer lies in their use of temperature and pressure to create the kinds of environments that are lethal […]
