Hospital Autoclave Sterilizers

Eighth post in series, “Autoclave Sterilization Basics”

Large autoclaves are essential to every hospital’s functionality. As we learned in our post about preventing the spread of infections in hospitals, the autoclave, also called a steam sterilizer, ensures the sterilization of medical instruments and materials used everyday in surgeries, procedures, and patient services.

In this post we will explore the ins and outs of large autoclave sterilizers, designated by the classification of EN 285 by the European sterilization standards and ANSI/AAMI ST79 by the American standards. Large autoclaves are found primarily in sterile processing departments, ambulatory surgery centers, laboratories and other medical clinics that require a large autoclave chamber for high-volume autoclaving.

How Does a Large Autoclave Work?

Let’s take a look at what happens inside one of these remarkable sterilizer machines. (The process is actually quite similar to the Class B tabletop autoclave, which we covered in our previous post.)

Just like with a conventional oven, we first need to preheat the autoclave, so it’s nice and hot when we are ready to sterilize the first load of the day. Once the autoclave is preheated via the autoclave jacket, we are ready to sterilize… (More on autoclave jackets later in this post.)

  1. We insert the load to be sterilized, set the autoclave to the appropriate cycle, close the door, and initiate the cycle.
  2. The first phase is removing the air from the autoclave chamber by vacuum pump in a series of negative pulses. If we were to use three pulses of 20 kPa to extract the air, they would work like this:
    1. The first pulse would extract about 80% of the air, leaving 20%.
    2. Then in the second pulse, 80% of the 20% remaining would be extracted (leaving 4% of the initial air).
    3. And finally the last pulse would remove 80% of the last 4% of air, which ultimately leaves 0.8% of the original air in the chamber.

    The bottom line is that each pulse removes 80% of the air, so that with each pulse, the amount of air inside the chamber gets much smaller, leaving us with a final number of more than 99% total air removal. This whole process is called fractionated pre-vacuum air removal. Additionally, it gets rid of air pockets and evenly distributes the steam throughout the entire load and chamber.

  3. Now we begin the heat-up phase with positive pulses for distributing the heat and ensuring that every type of material, especially in a mixed load of plastics, stainless steel, aluminum, and glass, which have extremely different heat emissions, will reach the sterilization temperature. Positive pulses (as opposed to negative pulses, which remove air) pressurize the chamber by steam. The number of pulses are determined by the type and size of the load.
  4. The actual sterilization process begins now, also known as holding time. The pressure and temperature remain constant during this phase.
  5. At the end of holding time, sterilization is complete. Next the exhaust valve releases the pressure back to atmospheric pressure.
  6. We have reached the drying stage. The vacuum pump sucks out the moisture on the load by decreasing the pressure to lower than atmospheric pressure. In this way we create a vacuum inside the chamber and lower the boiling temperature to less than the actual boiling temperature of 100℃ (at sea level). This lower boiling temperature causes the water to evaporate into a gas, which is extracted by the vacuum pump, and behold, the load is dried!
  7. We have now reached the last stage, in which we equalize the pressure inside the chamber with the atmospheric pressure outside. Filtered air enters the chamber by way of a HEPA filter (at 0.2μm), which breaks the vacuum, so to speak, and returns the chamber pressure to ambient pressure.
  8. The sterilization cycle is now complete, and it’s safe to remove the load from the chamber.

Keeping the Chamber Hot with Autoclave Jackets

What is a jacket? The jacket is a stainless steel wall that surrounds the entire autoclave chamber. The space between the jacket wall and the chamber is filled with circulating steam to maintain the level of heat of the chamber walls.

In large autoclaves, we use jackets to preheat the stainless steel walls of the chamber in order to reduce the heating time and reduce the amount of steam that must be injected into the chamber. In addition, the jacket improves the drying stage by irradiating heat to the chamber in order to assist in the evaporation of moisture. This limits condensation during the prevacuum/heating phase; the more condensation there is, the wetter the load will get and the more difficult drying is.

In addition, the jacket isolates the chamber from colder ambient temperatures and prevents cold spots in the walls of the chamber, thus maintaining uniform heat distribution. 

To get a visual demonstration of the jacket, check out our video about large autoclaves here.

Maximizing Large Autoclave Capacity with Space Constraints

Large autoclaves can range in size from 120 to 1300 liters. The question of which size to buy is generally complicated by the layout of the room in which the autoclave(s) will operate. Often hospitals, clinics, and laboratories need autoclaving solutions that maximize sterilization capacity in tight spaces.

In many European countries, steam sterilizers are designed to maximize STU capacity as efficiently as possible. STU is the standard measuring unit of autoclaving, measured in 30x30x60cm blocks. 

Autoclave doors and control panels can be built in the most space efficient way possible. For example, though the control panel usually appears on the side of a large autoclave, it can be designed to be on top to make the machine narrower and thus a better fit for a tight space.

Large Autoclave Door Options

Another way to customize large autoclaves is with one of these four styles of one or two doors:

  1. R Door: Regular manual hinged door
  2. A Door: Automatic hinged door
  3. V Door: Vertical sliding door
  4. H Door: Horizontal sliding door
Large Autoclave Medica Sterilizer - Sterilization Basics - TuttnauerVertical Sliding door
Automatic Hinged Door Larg Autoclave Sterilizers - Sterilization Basics - TuttnauerAutomatic Hinged Door

Pass-Through Autoclaves

Many sterile processing departments have three distinct areas: dirty, clean, and sterile. Used surgical equipment comes straight from the operating room covered in bodily fluids and must be cleaned. This occurs in the “dirty” section of the department. After the equipment is thoroughly cleaned of all visible dirt, bodily fluids, etc., it is then disinfected in washer disinfector machines, which are located between the “dirty” and “clean” sections. Finally, once disinfection is complete, the equipment is ready for sterilization in an autoclave, which takes place between the “clean” and “sterile” areas, divided by a single or double wall separation. Disinfected equipment enters from a door facing the clean area and exits from a different door facing the sterile area. Also known as a pass-through autoclave, this system of two separate doors on each side of the autoclave allows for sterilized equipment to remain sterilized and not become recontaminated in the “clean” section of the department. By emerging in the “sterile” section, the autoclaved equipment is ready to be brought back to the OR or stored for future surgery.


How are large autoclaves installed? There are generally two methods.

The most common method is floor-standing autoclave installation. These autoclaves stand on the floor of the facility. Typically, the bottom of the chamber is about 90 cm above the floor.

The other type of installation is pit-mounted. A pit-mounted autoclave is installed in a pit in the floor so that the floor of the chamber aligns with the floor of the facility. This is advantageous for big and/or heavy loads, which can be loaded and removed easily by rolling the cart into the autoclave chamber. This type of installation is available for bulk large autoclaves, which are up to 18,000 liters.

The Rundown on the Large Autoclave

With its substantial capacity, the large autoclave is designed to process loads reliably and efficiently. In this way, large autoclaves are able to keep up with the high-volume demands of hospitals, and other medical/scientific settings.

Let’s review: we explored each step in the sterilization cycle:

  • Air removal by negative pulses
  • Pressurization of the chamber by positive pulses
  • Sterilization time
  • Release of pressure
  • Drying stage
  • Break of vacuum and end of cycle

We then investigated the autoclave jacket and why it is necessary to prevent cold spots inside the chamber. We also looked at how large autoclaves can be custom-built to fit narrow spaces. By providing different options in the layout of the sterilizer, for example with doors and control panels, sterile processing departments are able to make the most of their cramped quarters.

And that’s the rundown on the large autoclave. Come along with us on our next post about laboratory autoclave applications.

Comments and questions are welcome, as always, in the comment section below.


Rio Olympics 2016: No Medals for Infection Prevention

The curtain on Rio’s 2016 Olympics rose August 5, 2016, in the shadow of new threats that seem to break into the media’s headlines each day. First there was the Russian doping scandal, then there were the athletes who were robbed at gunpoint on the streets of Rio. Terrorism is also a topic of concern, as Brazilian police have arrested 10 ISIS terrorists plotting attacks during the Olympics.  And in the background is Brazil’s unsettled political climate with a two year recession, and its President Dilma Rousseff facing an impeachment process.

All these issues are of concern and were widely covered by the media. Our blog, however, focuses on sterilization and infection control, so we will track these issues in the Rio Olympics. Often this topic does not grab headlines unless some catastrophe happens. Unbeknownst to many, there are actually several problems related to sanitation and infection control that are of immediate concern in Rio.

It Takes a Village to Host the Athletes

In the media we see the glorious moments of athletes reaching new heights, but what about all the behind-the-scenes work? Like where do all the athletes, coaches and staff stay? The Rio Olympic Village is an accommodation center built to house all participating athletes, as well as officials and athletic trainers. With a capacity of 17,950 people and a total of 3,604 apartments and 31 buildings, it is one of the biggest Olympic Villages in the history of the Olympic Games.

And properly maintaining such a large accommodation center has its challenges. For example, the sanitary conditions in the Olympic village are problematic due to poor plumbing. The head of Australia’s delegation raised concerns over blocked toilets, leaking pipes and exposed wiring inside the complex of the Olympic Village. The implications of bad plumbing can amount to diarrhea or other diseases carried by unsanitary leaking water.

Another severe problem is the contaminated waters. Athletes taking part in water-based events must also contend with human waste being dumped into the city's waterways, and especially Guanabara Bay, where all open-water events will be held. Rio de Janeiro environmentalist Andrea Correa is well aware of the problem, as she was quoted in The New York Times: “Our biggest plague, our biggest environmental problem, is basic sanitation, The Olympics has woken people up to the problem." Recent tests by government and independent scientists revealed a veritable petri dish of pathogens in many of the city’s waters, from rotaviruses that can cause diarrhea and vomiting to drug-resistant “superbacteria” that can be fatal to people with weakened immune systems.

Guanabara Bay is highly polluted

Government officials and the International Olympic Committee acknowledge that, in many places, the city’s waters are filthy. But they say the areas where athletes will compete — like the waters off Copacabana Beach, where swimmers will race — meet World Health Organization safety standards. During a surfing competition here last year, about a quarter of the participants ended up with nausea and diarrhea. When Brazil won the 2009 bid for the Olympic Games, it pledged to spend $4 billion to clean up 80 percent of untreated sewage. In the end, the government spent just $170 million.

On top of these serious health risks is the Zika virus. Engendering worldwide concern, Zika has caused a number of athletes to withdraw from the Olympic Games. What’s all the fuss about? Who’s at risk? What are the risks? Let’s answer these questions and more about the biggest health scare of 2016.

What is Zika? A short Intro

Let's start with the basics: Zika disease is caused by the Zika virus that is spread to people primarily through the bite of infected Aedes aegypti and Aedes albopictus mosquitoes. The most common symptoms of Zika are mild fever, skin rash, joint pain, conjunctivitis (red eyes), malaise, and headache. Rarely, it can cause brain and autoimmune problems. Symptoms usually show up in 3-12 days, but 60-80% of those infected show no symptoms at all. Zika has been found to still be active in semen 60 days after exposure, and men are advised to wait six months before engaging in sexual intercourse, even if using protection. Brazil has been hardest hit by the disease outbreak, and many physicians, competitors and potential visitors have expressed fears the Olympics could serve as a catalyst to spread the virus globally. Brazilian researchers say they believe that Zika, which has been linked to severe birth defects, came to their country during another major sports event — the 2014 World Cup — when hundreds of thousands of visitors flowed into Brazil. Virus trackers there say that the strain raging in Brazil probably came from Polynesia.

Is Zika Virus Curable?

There is currently no vaccine or treatment for Zika, which is spread primarily through the bite of an infected mosquito. The virus can also be spread through sexual transmission.

At first glance Zika doesn’t seem to pose a serious threat. In agreement with this claim is Professor Jimmy Whitworth from the London School of Hygiene and Tropical Medicine, who claims that “Zika is usually a mild, short-lived viral illness. In fact, most people don’t even realize they’ve been infected.” Although the Zika virus remains in the system for a few months, one wouldn’t expect to feel more than sore eyes, a few rashes and the odd muscular ache. (So if you’re visiting Rio for the Olympics you should probably worry more about muggings :-))

So Why Panic?

The biggest danger is for women who have been exposed to Zika. Children conceived when Zika is contracted are at risk of being born with microcephaly, a condition causing babies to develop smaller-than-normal heads, leading to deformities and brain damage.

Are the Athletes Right to Bail?

Although Zika has been around since 1940, it was largely dismissed as a major health concern until enough cases cropped up that scientists made the connection to microcephaly. Besides the likelihood of babies contracting microcephaly when their mothers were exposed to Zika, it's not clear if there are any other serious long-term ramifications. In terms of other, possibly more dangerous health problems, Zika won’t top the list for the majority of athletes; they may be more likely to contract a gastrointestinal bug. But that doesn’t mean precautions to lower the risk of Zika exposure shouldn’t be taken.

Risk Assessment at the Olympics

The 2016 Olympic Games in Rio attract 10,500 competing athletes and as many as 500,000 visitors. The question is does Zika pose a real threat to those attending the Olympics? There is no clear consensus. We will explore both sides of the issue. 

Why Zika Virus Poses a Real Risk for Olympics Attendants

On May 2016, 150 members of the international academic community recommended that the Olympic Games in Rio be canceled or relocated on the grounds of preventing the spread of Zika. Some athletes have also said they will not travel to Rio to compete due to health concerns associated with Zika.

Why Zika is not a real risk for Olympics Attendants

Most officials, including the World Health Organization, claim that the risk of Zika virus infections at the Olympic Games is both low and manageable. The Zika virus poses a negligible health threat to the international community during the Olympic Games in Rio de Janeiro, Brazil, according to researchers at the Yale School of Public Health (YSPH). In a worst-case scenario, an estimated 3 to 37 of the thousands of athletes, spectators, media, and vendors traveling to Rio for the Olympics will bring the Zika virus back to their home countries, the researchers concluded. The findings support the position of the World Health Organization, which has said that travel to and from the Olympics will not play a significant role in the international spread of Zika. Yale School of Public Health noted that Zika virus may not be as scary as the media portrays it to be—at least not in Brazil. A visitor’s probability of contracting the Zika virus is 1 in 56,300.

What precautions are taken to protect the public at the Olympics?

The Zika virus, which is spread predominantly by mosquitoes, is currently widespread in Rio de Janeiro. Mosquito nets were provided over the beds in the athletes’ village and all the venues will be made as mosquito-proof as possible. Around 17,000 international athletes, volunteers and staff have been tested in the Brazilian capital and so far none have contracted Zika, but some athletes aren’t taking any chances.

Tips that Will Reduce the Risk

  • Use insect repellent and wear light-colored clothing that covers as much of the body as possible.
  • Choose air-conditioned or screened-in accommodations where windows and doors are usually kept closed to prevent mosquitoes from entering.
  • Use condoms while attending the Games and for at least 8 weeks after returning. If one’s partner is pregnant, use condoms throughout her pregnancy.
  • Avoid visiting areas in cities and towns with no piped water or poor sanitation, where the risk of being bitten by mosquitoes is higher.

Tips for staying healthy in Rio Olympics

Who Pulled Out of the Olympic Games?

Although WHO has determined the Zika virus to be of very low risk, there were some athletes who prefered not to take the chance and have withdrawn from the games. Also some journalists and potential attendants avoided Rio for fear of Zika exposure. A list of disciplines and athletes boycotting the Rio Olympics due to their fear of Zika exposure are:

♦ Tennis:
  • Canadian number-seven champ and Wimbledon finalist Milos Raonic
  • Czech tennis star Tomas Berdych 
  • Romanian number five-ranked Simona Halep
♦ Golf is back on the Olympics for the first time in over 100 years. Or is it? The world’s top four players have cited Zika virus as their reason for pulling out.
  • Jason Day
  • Jordan Spieth
  • Rory Mcllroy 
  • Dustin Johnson
♦ Cycling:
  • Tejay Van Garderen
♦ Basketball:
  • LeBron James
  • Stephen Curry 

Not only athletes withdrew from the games, but also many visitors decided to skip the current Olympics. Probably the most famous are Duchess Kate Middleton and Prince William who were planning to go to the Rio Olympics 2016, but the royal couple decided not to travel to Brazil, which was hit hardest by the virus.

As the olympic games are well into the first week no Zika cases have been reported. But Zika and other health hazards are lurking over the olympics. Zika already had an economic toll in the form of 1.2 million unsold tickets to the Olympic Games. We hope that the only drama that arises is from the competition itself. Good luck world!


EN 13060 Class B Tabletop Autoclaves

Seventh post in series, “Autoclave Sterilization Basics”

Class B autoclaves are great space-savers built for high performance. They are microwave-sized autoclaves that fit easily on the counters of busy clinics and dental offices. Available in the compact sizes of 19 and 29 liters, the Class B is the top-of-the-line of tabletop autoclaves.

Essentially they are a miniature version of the larger EN 285 autoclave found in hospitals. The industry consensus about what the “B” in Class B stands for is “big,” not as a reference to size, but rather as a reference to performance. Class B tabletop autoclaves are expected to offer the same advanced performance as the much larger hospital sterilizers EN 285.

The main advantage of Class B autoclaves is the use of a vacuum pump for both removing air and drying the load. Class B autoclaves are able to remove more than 99% of the air inside the chamber, ensuring no trapped air that would prevent steam from reaching the load surface, thus killing microbial life on the load, without external hookups to water or steam (some tabletop autoclaves are connected to water pipes for auto-filling, so operators don’t need to fill them). In other words, the Class B tabletop autoclave is the most advanced “plug-n-play” model on the market today.

Elara 9 D - High Speed Class B Tabletop Autoclave - TuttnauerTuttnauer Elara 9D, Class B Tabletop Autoclave

How Does the Class B Autoclave Work?

1. First we remove the air. How? By use of a vacuum pump, the Class B autoclave uses vacuum pulses to extract the air in the autoclave chamber. This process is able to remove more than 99% of the air inside the chamber.

Let’s say we are going to use three pulses to extract the air. The first pulse will extract about 80% of the air, leaving 20%. Then in the second pulse, 80% of the 20% remaining will be extracted (leaving 4% of the initial air). And finally the last pulse will remove 80% of the last 4% of air, which brings us to the low overall number of 0.8% of air left in the chamber. In other words, each pulse extracts 80% of the air, so that with each pulse, that number gets much smaller, leaving us with a final number of 99% total air removal. This whole process is called fractionated pre-vacuum air removal. It eliminates air pockets and thus improves the penetration of the steam into the deepest point of the load.

Elara 9 D - High Speed Class B Tabletop Autoclave - TuttnauerIn this graph you can see the pre-vacuum air removal pulses (in pink) achieved by the built-in vacuum pump

2. After the vacuum pulses have removed almost all of the air inside the chamber, the pressure and temperature increase.

3. We have now reached the sterilization stage where the temperature and pressure are held constant for the duration of the sterilization time, also known as holding time. This is the phase when the actual sterilization takes place, i.e., goodbye to germs.

4. Next the exhaust valve releases the pressure to atmospheric pressure.

5. The last phase is the drying phase in which the load is dried completely. Again we use the vacuum pump, but this time the vacuum pump sucks out the moisture on the load. How? By decreasing the pressure to lower than atmospheric pressure, we create a vacuum inside the chamber and reduce the boiling temperature to lower than the actual boiling temperature of 100℃. This lower boiling temperature makes the water evaporate into a gas, which is then sucked out by the vacuum pump, and voilà, the load is dried!

At this point, sterilization is complete, the load is dry, and the autoclave is safe to open.

Autoclave Cycles

There are generally two cycles for autoclaving in a Class B tabletop autoclave:

  1. The standard cycle lasts about three minutes and reaches 134℃. This cycle is intended for standard materials like glassware or metal solids, hollows, porous items and textiles.
  2. The delicate cycle lasts fifteen minutes and operates at the lower temperature of 121℃. This cycle is designed for delicate materials like plastics and other delicate items that would not be suitable for the standard cycle.

Be Ready to Use Your Class B Tabletop Autoclave

Let’s review what we just learned about Class B autoclaves. We explained that the main advantage of Class B autoclaves is the use of a vacuum pump for extracting air before sterilization and drying the load after sterilization. We showed how the Class B autoclaves use a set of pulses to extract about 99% of the air inside the chamber, called fractionated pre-vacuum air removal. We looked at each step in the autoclaving process to understand exactly what happens inside the chamber when the cycle takes place. And finally, we described two common cycles, the standard and delicate cycles, and for which materials we would use each of them.

Check out our next post in this series in which we will explore large autoclave sterilizers (EN 285) found in hospitals, medical centers, laboratories and other industries that require sterile processing.

Comments and questions are welcome, as always, in the comment section below.