How to select an Autoclave for your pharmaceutical applications

What is an Autoclave and its importance?

An autoclave is a device that sterilizes different items and pharma products using steam. The steam is applied under high pressure, generating high temperatures. High temperatures and pressure effectively eliminate harmful bacteria and microorganisms. Relative to temperature, pressure is also necessary as a part of sterilization requirements, which facilitates achieving the desired temperature.

The sterilization temperature is pre-defined and is set after thorough study and validation by the quality department, and it is necessary to keep this temperature. Otherwise, the sterilization will become ineffective, and the items will still contain harmful bacteria and microorganisms.

The typical steam temperature is 121°C for about 30 mins at 15 psi of steam pressure. 

The sterilization occurs in a three-phase cycle, each with definite application, and includes the following.

Pre-Vacuum Cycle - in this cycle, the air is removed from the chamber to create a vacuum inside it. It removes air pockets for easy steam flow inside the chamber. This cycle is applied more than once, typically three types

Sterilization Cycle: In this cycle, steam is applied to the chamber to achieve the desired temperature. In addition to temperature, pressure is also maintained for a pre-defined value. Temperature is kept for a specified time, and after the timer has elapsed, the temperature is decreased to end the sterilization process.

Post - Vacuum Cycle - in this cycle, steam is removed from the chamber to cool it, and items can be easily removed. 

After completion of the post-vacuum cycle, the chamber door is opened to empty the chamber for further process. ,

Autoclaves also consist of instrumentation critical to the equipment's safety and process performance, such as temperature and pressure. 

Temperature is used to monitor chamber temperature and serves two purposes, 

• Ensure accurate sterilization temperature throughout the process and prevent deviation from these  values. This is ensured using a controller that continuously monitors and compares the temperature sensor value with the set value. If there is a deviation, it adjusts it by opening or closing the steam valve.

• Prevent damage to the autoclave due to overtemperature. This is achieved by using a central controller that continuously monitors the temperature sensor, and if it exceeds the safe threshold value, it immediately halts the process.

The pressure sensor monitors the steam pressure inside the chamber and adjusts the pressure according to the set value. Additionally, if chamber pressure becomes abnormally high due to any malfunction, it also sends a signal to abort the process to prevent damage to the autoclave. 

Like other pharma equipment, a central controller operates the autoclave and other automation components, such as the machine Interface, Sensor, and valves. 

At the end of the cycle, a recording device records all the critical parameters, such as temperature and time. This is necessary to ensure the process's integrity and to present it to the regulations during their routine inspection.

Some considerations to look for when selecting an Autclave

Laboratory scale vs. commercial scale

Considering the scale of operation is the first step when selecting an autoclave. Like many other pharma equipment autoclaves are also used in Quality labs and R&D sections of pharma organizations with different specifications from commercial ones. However, their application and work remain the same.

• Laboratory-scale autoclaves have much smaller chamber sizes and the resulting autoclave capacity.

• In addition, there are multiple chamber loading and off-loading profiles, such as front-loading and top-loading. Its selection depends on the item types.

              ◆ Top loading is preferred for liquid or glassware loads

              ◆ While front loading is preferred for items of various sizes.

• They also have less energy requirement compared to those on a commercial scale. Other than that, their operational parameters, such as temperature and pressure, remain the same. 

Commercial-scale autoclaves have much higher physical and chamber dimensions. Their capacity is also very high, and they can autoclave entire batches. Power requirements, such as electrical power and heat, are much higher than the laboratory scale.

Operational parameters

Operational parameters are the ability of an autoclave to achieve the sterilization for which an autoclave and product are designed. 

As described earlier in the article, the autoclaves must achieve operational parameters without difficulty and consume extra resources.

Capacity

The autoclave's capacity is expressed in liters since it resembles vessels. 

The capacity of the autoclave must match the production requirements of the area in which it is installed. For capacity, the buyer should communicate the current production requirements to the manufacturers, who will translate it to its existing model.

Safety features

Safety features are critical for every equipment in the pharmaceutical industry, and there is much more of a requirement for autoclaves. An autoclave is a closed chamber with pressurized steam. It can become deadly if steam pressure exceeds the maximum limit of the equipment's capacity, which can happen due to operational errors. Under this condition, the autoclave chamber can explode, causing tremendous destruction and even becoming deadly. Additionally, safety features also protect the products or items inside the chamber. 

Investing in maximum safety devices is always beneficial for man, material, and machine.

Some safety features for autoclaves include but are not limited to

• Over temperature - This safety is activated when chamber temperature exceeds the set value. In this case, the visual and audible alarm is generated, and the process is stopped in severe conditions.

• Overpressure - This safety is activated when the chamber pressure exceeds the set or threshold value. An audible and visual alarm is activated, indicating the over-pressure. The process is also stopped to prevent damage. 

• Pressure Safety Valve - A pressure safety valve is activated when the chamber’s pressure exceeds the design pressure. The valve's activation pressure is the chamber's over-pressure condition to release excess steam from the chamber automatically.

• Door Interlock - this safety ensures that the door(s) is locked before starting the process. During the process, if the door is opened, it is sensed by this safety, and generates an alarm.

• Less / No water - when the steam generator is used to generate steam, this safety indicates the absence of water in the boiler, preventing the boiler from dry running and causing damage to the boiler.

• Indicating Gauges - in addition to safety devices, mechanical gauges are also installed to monitor physical variables, such as temperature and pressure. They help keep an eye on the process.

Recording Device

Record keeping is an integral requirement for the pharma industry, and regulatory bodies review it. The entire sterilization process must be recorded in a presentable way.

The recording device records the chamber's temperature against time and the current pressure inside the chamber. Recording is continued during the entire process, 

After completing the process, the recording is finished, and the record is maintained. 

The recording can be paper-based or digital. 

In paper-based, a recorder draws the graph on the paper or prints on the paper against the time and existing pressure. 

In digital, the process is recorded digitally, which can then be stored in digital memory devices.

Steam supply - External Vs. Internal

There are two standard methods of supplying steam: internal and external.

In the internal method, a steam generator generates the steam, which is commonly part of the autoclave. The heating source is commonly electrical, which heats the water until it is converted into steam. This allows the autoclave to be operated even when no steam is in the plant. However, it requires a constant water flow ( purified or WFI) to produce steam, and its power requirements are also higher due to the inclusion of heaters. 

In the external method, a boiler is used to supply steam to the autoclave through an appropriate piping network. The steam supply characteristics depend on the boiler steam characteristics.

Double Door Vs. Single Door

Double-door and single-door autoclaves characterize the autoclave according to the door design. 

A double-door autoclave has two doors - one for loading items and the other for unloading the items.  When used for sterile filling purposes, the un-loading door opens the sterile area so that items can be directly processed for further processing without exposing them outside the clean area. 

In a single-door autoclave, there is only one door from which loading and unloading occurs. 

Validation Port

The validation port is an opening in an autoclave that allows the temperature measuring device to be inserted inside the DHS chamber. Its main aim is to record temperature values and verify its performance according to the design parameters.

What can go wrong if an autoclave is not selected appropriately?

Some common problems that we might face if not selected appropriately include

• An autoclave will fail to provide the desired operational parameters, such as temperature and pressure, which will, in turn, disturb the sterilization cycle and affect the product. 

• Chances are that the autoclave could become dangerous due to abnormal behaviors, which will have consequences.

• It will decrease the ability of steam to provide the required temperature, which will increase the sterilization cycle, causing wet load or no sterilization at all

• Poor autoclave performance will result in regulatory actions, such as warning letters, and can even suspend production operations.