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Succeed in steam sterilization

Matters needing attention

Now let’s look at five common mistakes.

1.Don’t create a plateau. These points are just potential dead ends. Vapor is usually introduced into the container through nozzles from other nozzles away from the top of the container. The air seems to be stubborn at high points and is not always predictable. I’ve seen peaks at 3 L/d ratios fail to reach the temperature, while peaks at 9 L/d ratios do. Because of this unpredictability, it is best to design forward sweep steam streams at all these points.

2.Don’t believe that air flows downward according to gravity. The molecular weight of air is 29 and the molecular weight of steam is 18. Therefore, it is thought that air falls naturally from high places and is replaced by steam. Steam turbulence is required to disperse the air and steam flow to remove the air from the system during the sterilization time range.

3.Don’t create a dead end. When designing a pipe for steam sterilization, it is easy to create areas of cavitation formation, so that the steam is not fully permeable and cannot reach the appropriate temperature. These dead corners are a problem because if air is present, it may not be possible to sterilize. The only way to really detect a dead end is to measure the temperature or indicate that the spore strips have not been killed.

4.Don’t create overheating conditions. Steam sterilization using superheated steam requires dry heat temperature and time conditions (higher temperature and longer time) and does not follow the wet heat sterilization kinetics.

Two ways to create hot and dry conditions are:

An external source is used to heat the saturated steam to superheat. One example we often watch out for is an autoclave with a steam jacket. Control must be carried out to ensure that the temperature of the steam jacket is always lower than the steam sterilization temperature in the autoclave room to avoid overheating in the room.

To cause a rapid descent of steam (e.g. through a pressure reducing valve). Even if the steam is under lower pressure, it can still retain its heat and thus form an overheated state. Normally, the normal heat loss of the system will restore the vapor to saturation before it reaches the equipment to be sterilized. I have never encountered dry heat in a sterilization facility, but this is what I suggested to a colleague: remove the insulation from the pipe near the pressure relief valve (if it is unlikely that someone will be scalded); Move the pressure reducing valve further upward; Reduce steam pressure or install cooling heat exchanger in stages to eliminate overheating.

5.Do not use regular drains. There is a temptation to connect drainage lines together to save on pipeline costs. Do not do this or at least minimize it before steam traps. In parallel lines, enough steam may flow through one line but not through the other. Drains can be connected behind steam traps if the pipe is large enough to carry condensate water and some leaking steam without creating measurable pressure in the pipe.

The following seven factors are critical to successful sterilization.

1.Expel air from the system. Effective damp heat sterilization depends on saturated steam conditions. When air is present in the system to be sterilized, the saturated vapor temperature and pressure conditions no longer apply.

The air dilutes the steam and applies a lower temperature than expected at a given pressure. Trapped pure air completely prevents steam contact and provides dry heat sterilization conditions. Using saturated steam, one minute of killing was recorded at 121.1°C. The lower temperature takes longer to achieve each F0. Dry heat sterilization conditions require higher temperatures and longer time to produce a kill record.

Two methods are commonly used to eliminate air:

Pre-vacuum circulation. Before the introduction of steam, autoclaves usually rely on vacuum pumps to remove air from pipes, pipes, equipment, clothing, gauze fillers, and chambers. The cycle in which steam is injected after vacuum is often referred to as “prevacuum”. A series of three pre-vacuums is usually sufficient to remove air as long as there are no major leaks. The advantage of the pre-vacuum cycles is that they remove air from porous materials and potentially deeper “dead ends.” The disadvantage is that vacuum pumps must be purchased and maintained.

Steam turbulence and flow. If no substance is present that would trap the air, no vacuum circulation is required. Many autoclave loads and most fermenters and piping systems can be sterilized using “gravity circulation”. The method relies on steam flowing through the system in a directional manner to ensure air is blown out of the system. Steam flows from the entry point to a trap, orifice, or through a valve that allows air, condensate, and steam to leave the system. The ducts are designed with a minimum number of pockets or dead ends to capture air.

One technique for removing air from stagnant areas is to introduce steam by destroying the air and then sweeping it out of the system. The most common location for air retention is a high point that does not exit through a trap or orifice. For example, during the fermentation process, it is important to ensure that nozzles at the top of the tank (containing agitator seals and other ports) do not trap air. Sending steam through a nozzle is one way to eliminate air. Designed to allow steam to flow out through one nozzle into one trap is another. A third method is to draw in steam from another port and point it at a nozzle where air is suspected to be trapped. Steam creates turbulence and disperses air. The steam flowing through the rest of the system (if properly designed) will take the air away.

Systems that need to be sterilized can become very complex, especially when ductwork must be included. Visualizing steam flow and sequencing automatic valves to guide steam flow according to defined flow patterns is therefore an important check in the design process. Also, choose valves without cavitation, such as diaphragm valves.

The advantage of using steam turbulence and flow is that no vacuum pump is required. The disadvantage is that more design skill is required to ensure proper steam flow.

2.Place trap or orifice at low point to drain condensate and ramp lines into them. All true low points in the system to be sterilized should have a steam trap or an outlet for condensation. Otherwise, the steam cools and becomes a condensate below the required sterilization temperature, making it impossible to sterilize the system. The key is to identify all the low points and design the traps or orifice. In addition, the inclined line toward the low point minimizes the buildup of condensate and allows it to be discharged.

Condensation is unavoidable when saturated steam is used, because it forms whenever steam condenses to heat an object or surface. The condensate will be sterile if it remains at the desired temperature for the required time. When it is difficult to maintain the temperature of condensate water in a low pressure line, the solution may be to increase the pressure of steam entering the system, thereby increasing the temperature of the low pressure line. The pressure of steam, the speed at which steam and condensate flow through the orifice plate or trap, the size and slope of the low line, the amount of insulation, and the amount of condensate to be removed all affect the low point. The given sterilization temperature can be maintained.

3.Place temperature indicators at low points and key points. Temperature indicators, usually permanently placed RTDs, provide process engineers with a real-time and ex post troubleshooting method to determine whether the system is properly sterilized during routine production. The trap may fail, the valve may remain closed, and the orifice may become clogged. As a result, a system that was sterilized yesterday may fail today. Temperature indicators are placed at each low point where orifice or trap exists to detect and automatically alarm when temperature conditions are not met. Adding more equipment adds to the cost, but also increases the guarantee of sterility. Permanent placement of temperature elements at other critical locations — at the steam source, in the sterilized container, or at a site of concern — also AIDS in monitoring the sterilization process.

4.Create a system that is as leak-free as possible. All systems should be leak tested before and after sterilization. The spill is bad for several reasons:

Pressurized air may leak into the system and invalidate saturated vapor conditions, or a slight vacuum formed during cooling may introduce microorganisms after sterilization.

In addition, during fermentation, the leak may fill the medium, providing a stagnant “fuse” through which foreign organisms can enter the fermenter.

Steam and condensate may leak out of the system and pose a safety hazard.

The last system I designed performed a computer-aided three-level leak test after the steam sterilization phase. This test ensures that leakage in and out of the system is minimized and that critical valves do not leak when closed, thereby eliminating the risk to the products contained in the system.

Leakage occurred. No leaks are good, but not all leaks lead to pollution. A leak can increase the chance of contamination or reduce the guarantee of sterility. My experience at fermentation pilot plants has shown that not all leaks are the same when it comes to contamination. A high contamination rate occurs when sterile air enters the fermenter from an external source and a leak is detected in the air line. I suspect the Venturi effect caused non-sterile air from the outside to be sucked into the fermenter, contaminating it. However, leakage from the nozzles at the top of the tank resulted in a very low contamination rate.

5.After sterilization, follow the steam with sterile air and maintain positive pressure. After the steam sterilization cycle is complete, sterile air is introduced into the system. If this is not done, when the steam flow stops, the steam will condense and begin to form a vacuum in the system. This vacuum can cause a potentially high incidence of contamination by inhaling non-sterile air from the outside through leaks. Once there is pressure in the system (I recommend 3 to 5 psig), maintain that pressure. It is used as a sterile assurance measure, increasing the likelihood that a leak will flow out rather than inward.

6.Design the system to be easy to clean. In pharmaceutical applications, this is a pretty obvious statement because the product needs to be kept clean. When the work is done manually, as is usually the case with the fermenter, improper cleaning will cause steam sterilization problems:

Clusters, media, or product layers may cause heating to be slower than expected or prevent steam penetration to sterilize the material or system.

Debris can cause the steam trap or orifice used for sterilization to fail to function properly.

7.Look for unexpected temperature changes. You could write a big article on the subject; Here, we can only describe the basics.

When verifying the sterilization of the system, numerous thermocouples are placed in the system along with the permanent temperature element to study the sterilization process. If two properly calibrated temperature elements in the same part of the system differ significantly from one another, there may be air, superheated steam, or excess condensate.

Always suspect and verify temperature element calibration first. Once it is confirmed that the temperature element has been calibrated accurately, if:

Condensation is suspected when the low point is below the sterilization temperature.

Saw below sterilization temperature at high point, suspected air problem.

The temperature is too high for the present pressure, and then the problem of superheated dry steam is suspected.

Unfortunately, when excessively low temperatures are observed, it is not always possible to distinguish the difference between trapped air and excess condensed water. For condensate water, as long as it meets the requirements of temperature and time, it will produce sterilization. However, if air causes a temperature change, it is assumed that no sterilization will occur. Developing the ability to detect temperature changes is important and requires experience. Other devices can detect the presence of air in the system, but temperature changes in the thermocouple can actually help locate the source of the problem.

No hard and fast rules are provided as to how much temperature variation indicates the problem of sterilization, but the concepts presented apply. When creating a standard for determining when a temperature change indicates a sterilization problem, consider the actual temperature element to be used and its given precision.

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