USP 797 has been implemented by compounding pharmacies, hospital labs, and other healthcare facilities for almost 20 years now. But maintaining sterility is still a common source of confusion, and as humans are the biggest source of contamination in a cleanroom, it is generally a process that must be vigilantly monitored, evaluated, and improved.
But with patient health and lives on the line, it is imperative that cleanrooms facilities themselves as well as tools, equipment, and cleaners be sterile.
As we review the types of sterlization below, take note of the links that will take you to additional resources for related product selection. Here we will not discuss cleaning methods such as rotating cleaners to maintain sterility as we have covered that in our cleanroom cleaning procedures checklist .
This information is a general overview and any changes to your Standard Operating Procedures (SOPs) should not be based on this high-level information. Do your due diligence.
Sterilization Using Steam
The most common and reliable method of sterilization in cleanrooms is using steam. It is the most popular method not only because it is extremely effective, but also, because it is very economical. And, though something we rarely think about with steam, but it is vitally important: it uses no chemicals so it is very ecological and safe for workers.
Steam should be used for specific durations at specific pressures for the material being treated (metal, fabric, etc.). Steam is quite effective because it kills all types of microorganisms quickly including bacteria, molds, yeasts, viruses, protozoa, and algae (including bacterial spores) and it permeates beyond surfaces such as on fabrics.
Typically, steam is utilized in a cleanroom through autoclaves. Autoclaves use high pressure and heat to steam-sterilize laboratory supplies, reusable apparel, components of equipment, and some liquids by steam-cleaning. The pressurized enclosure raises the temperature of water to above boiling making the water vapor efficient at killing most microorganisms.
Though common, convenient, and cost-effective, the autoclave has complexities that must be monitored to ensure that its steam sterilization functionality remains reliable. For example, the presence of air in an autoclave sterilization cycle reduces steam penetration of the materials being sterilized. cGMP calls for routine verification testing of air removal during the pre-vacuum cycle. The testing demonstrates that entrapped air is completely removed so that it cannot interfere with the effectiveness of the steam sterilization process. Failures of the air removal verification test indicate a need for maintenance of the autoclave to repair leaks in the chamber or piping.
Learn more about air removal verification testing, pulse cycles of steam sterilization, and other key concepts of autoclave function at this Cleanroom Technology steam sterilization article.
Sterilization Using Dry Heat
Dry heat sterilization utilizes super-heated air with minimal or no water in it. While less common, it offers many of the benefits of steam sterilization and even has some advantages over steam:
- less maintenance as there are no water pipes and only one utility, electricity
- saves space as there is no need for water pipes, drain, and pit that can take up valuable space in your facility
- less intensive technology results in less frequent repair and maintenance of seals, gauges, etc.
- more cost effective than steam
To sterlize an object, heat absorbed by the object’s exterior transferring the heat toward the center of the object until the entire object gradually reaches a temperature required to sterilize. The temperature depends on the type of material.
Sterilization Using Chemicals
Some cleanroom items such as delicate medical devices cannot take the heat of steam or dry heat sterilzation. In this case, sterilizing chemicals are utilized.
The most prevalent sterlization chemical used is Ethylene Oxide (EtO). EtO gas eradicates microorganisms.
View in full screen mode by clicking the arrows at bottom right of this slideshare on EtO sterilzation.
Wrapped objects are placed in a vacuum chamber similar to steam sterilization where air is removed and replaced with EtO. After the prescribed duration for sterilization (depending on type of object), the sterilant gas is removed and replaced with air.
This method of sterilization carries great risks as it is very dangerous to humans. It also is less efficient as the objects such as apparel treated with the dangerous gas must be quarantined during an outgassing period of usually a wekk but could be up to 14 days until residual EtO levels drop. Because of this, EtO is rarely any longer to sterilize cleanroom apparel as it is not as safe as other alternatives and extra apparel is required to accommodate the long cleaning cycle. Today, irradiation is used on most cleanroom apparel.
Other chemicals are used and new ones always being developed, but it is a challenging form of sterilization because of the dangers, inconveniences, and risks of using chemicals that damage devices or cleanroom facilities.
It is a frequent misconception that all sterilizers will do work on any device or application. But this is simply not the case. The manufacture of the objects to be sterilized cleaned should provide a list of chemicals that are acceptable to use as well as those that are damaging to them.
Sterilization Using Radiation
Various types of radiation including Gamma rays, ultraviolet (UV) light, and x-rays can be effective in eliminating microbes. Irradiation works by destroying microorganisms’ DNA rendering them harmless. UV light is a safer method than Gamma rays and x-rays, but its penetration capabilities are less. But it is a good choice for small areas with hard surfaces such as laminar flow hoods. In aseptic cleanrooms, (UV) irradiation is used to sterilize large areas.
View in full screen mode by clicking the arrows at bottom right of this slideshare on EtO sterilzation.
Gamma rays and x-rays are higher penetrating make them very effective for sterilization, but also much more dangerous to humans. Gamma irradiation is the high-energy ionizing radiation method most commonly used for sterilizing cleanroom apparel. Gamma rays emitted from the nucleii of a decaying radioactive isotope of cobalt, cobalt 60. Gamma rays’ electromagnetic radiation are similar to x-ray but with a shorter wavelength.
Gamma irradiation is common in large scale manufacturing of sterilized products such as our lint-free sterile wipes, sterile gloves, and sterile bunny suits. Cleanroom apparel and supplies such as wipes are cleanroom laundered, packaged, and exposed to gamma irradiation at a contract sterilizer until achieving the minimum dose specified.
There are two types of contract gamma facilities, continuous and batch. To determine the appropriate dosage a validation protocol in AAMI/ANSI/ISO 11137-1-2006 for the object to be sterilized is utilized to establish the correct dosage, formerly measured in rads and today measured in grays. Accurately determining the dosage needed to achieve the desired sterility assurance level is important as gamma irradiation is destructive so the minimum and maximum specified dose should be as low as practical.
Understanding how sterilization is used inside your cleanroom facility and on apparel, supplies, and equipment before they are delivered to your facility helps ensure you are better prepared to follow USP 797 and protect your patients. Our cleanroom consultants have direct access to top manufacturers’ representatives so any question you have that we don’t know, we can get your answer.