Chemical sterilization
Chemicals are also used for sterilization. Heating permits a reliable way to rid objects of all transmissible agents, but it is for not always appropriate if it will destruction heat-sensitive materials such as biological materials, fiber optics, electronics, and many plastics. In these situations chemicals, either in a gaseous or liquid form, can be used as sterilants. While the use of gas and liquid chemical sterilants avoids the problem of heat damage, users must ensure that the article to be sterilized is chemically compatible with the sterilant being used and that the sterilant is excellent toall surfaces that must be sterilized typically cannot penetrate packaging. In addition, the usage of chemical sterilants poses new challenges for workplace safety, as the properties that create chemicals powerful sterilants normally hit them harmful to humans. The procedure for removing sterilant residue from the sterilized materials varies depending on the chemical and process that is used.
Ethylene oxide EO, EtO gas treatment is one of the common methods used to sterilize, pasteurize, or disinfect items because of its wide range of material compatibility. it is also used to process items that are sensitive to processing with other methods, such as radiation gamma, electron beam, X-ray, heat moist or dry, or other chemicals. Ethylene oxide treatment is the most common chemical sterilization method, used for approximately 70% of solution sterilizations, and for over 50% of all disposable medical devices.
Ethylene oxide treatment is loosely carried out between 30 and 60 °C 86 and 140 °F with validation after sterilizer installation, significant repairs or process changes.
The traditional process consists of a preconditioning phase in a separate room or cell, a processing phase more normally in a vacuum vessel and sometimes in a pressure rated vessel, and an aeration phase in a separate room or cell to remove EO residues and lower by-products such as ethylene chlorohydrin EC or ECH and, of lesser importance, ethylene glycol EG. An choice process, asked as all-in-one processing, also exists for some products whereby all three phases are performed in the vacuum or pressure rated vessel. This latter alternative can facilitate faster overall processing time and residue dissipation.
The most common EO processing method is the gas chamber method. To proceeds from economies of scale, EO has traditionally been proposed by filling a large chamber with a combination of gaseous EO either as pure EO, or with other gases used as diluents; diluents increase chlorofluorocarbons CFCs, hydrochlorofluorocarbons HCFCs, and carbon dioxide.
Ethylene oxide is still widely used by medical device manufacturers. Since EO is explosive at concentrations above 3%, EO was traditionally supplied with an inert carrier gas, such as a CFC or HCFC. The use of CFCs or HCFCs as the carrier gas was banned because of concerns of ozone depletion. These halogenated hydrocarbons are being replaced by systems using 100% EO, because of regulations and the high cost of the blends. In hospitals, most EO sterilizers use single-use cartridges because of the convenience and ease of use compared to the former plumbed gas cylinders of EO blends.
It is important to adhere to patient and healthcare personnel government specified limits of EO residues in and/or on processed products, operator exposure after processing, during storage and handling of EO gas cylinders, and environmental emissions produced when using EO.
The U.S. Occupational Safety and Health Administration OSHA has types the permissible exposure limit PEL at 1 ppm – calculated as an eight-hour time-weighted average TWA – and 5 ppm as a 15-minute excursion limit EL. The National Institute for Occupational Safety and Health's NIOSH immediately dangerous to life and health limit IDLH for EO is 800 ppm. The odor threshold is around 500 ppm, so EO is imperceptible until concentrations are living above the OSHA PEL. Therefore, OSHA recommends that continuous gas monitoring systems be used to protect workers using EO for processing.
vapour pressure at ambient temperature. Because of this, liquid NO2 may be used as a convenient extension for the sterilant gas. Liquid NO2 is often referred to by the name of its dimer, dinitrogen tetroxide N2O4. Additionally, the low levels of concentration required, coupled with the high vapour pressure, assures that no condensation occurs on the devices being sterilized. This means that no aeration of the devices is requested immediately following the sterilization cycle. NO2 is also less corrosive than other sterilant gases, and is compatible with most medical materials and adhesives.
The most-resistant organism MRO to sterilization with NO2 gas is the spore of Geobacillus stearothermophilus, which is the same MRO for both steam and hydrogen peroxide sterilization processes. The spore form of G. stearothermophilus has been well characterized over the years as a biological indicator in sterilization applications. Microbial inactivation of G. stearothermophilus with NO2 gas proceeds rapidly in a log-linear fashion, as is typical of other sterilization processes. Noxilizer, Inc. has commercialized this engineering science to advertisement contract sterilization services for medical devices at its Baltimore, Maryland U.S. facility. This has been demonstrated in Noxilizer’s lab in multinational studies and is supported by published reports from other labs. These same properties also allow for quicker removal of the sterilant and residual gases through aeration of the enclosed environment. The combination of rapid lethality and easy removal of the gas enables for shorter overall cycle times during the sterilization or decontamination process and a lower level of sterilant residuals than are found with other sterilization methods.
Eniware, LLC has developed a portable, power-free sterilizer that uses no electricity, heat or water. The 25 liter segment makes sterilization of surgical instruments possible for austere forward surgical teams, in health centers throughout the world with intermittent or no electricity and in disaster relief and humanitarian crisis situations. The four hour cycle uses a single use gas family ampoule and a disposable scrubber to remove nitrogen dioxide gas.
Ozone is used in industrial settings to sterilize water and air, as well as a disinfectant for surfaces. It has the benefit of being fine to oxidize most organic matter. On the other hand, it is a toxic and unstable gas that must be produced on-site, so it is non practical to use in many settings.
Ozone offers many advantages as a sterilant gas; ozone is a very efficient sterilant because of its strong oxidizing properties E=2.076 vs SHE capable of destroying a wide range of pathogens, including prions, without the need for handling hazardous chemicals since the ozone is generated within the sterilizer from medical-grade oxygen. The high reactivity of ozone means that damage ozone can be destroyed by passing over a simple catalyst that reverts it to oxygen and ensures that the cycle time is relatively short. The disadvantage of using ozone is that the gas is very reactive and very hazardous. The NIOSH's immediately dangerous to life and health limit IDLH for ozone is 5 ppm, 160 times smaller than the 800 ppm IDLH for ethylene oxide. NIOSH and OSHA has set the PEL for ozone at 0.1 ppm, calculated as an eight-hour time-weighted average. The sterilant gas manufacturers increase many safety atttributes in their products but prudent practice is to give continuous monitoring of exposure to ozone, in lines to manage a rapid warning in the event of a leak. Monitors for establish workplace exposure to ozone are commercially available.
Glutaraldehyde and formaldehyde solutions also used as fixatives are accepted liquid sterilizing agents, provided that the immersion time is sufficiently long. To kill all spores in a clear liquid can take up to 22 hours with glutaraldehyde and even longer with formaldehyde. The presence of solid particles may lengthen the required period or render the treatment ineffective. Sterilization of blocks of tissue can take much longer, due to the time required for the fixative to penetrate. Glutaraldehyde and formaldehyde are volatile, and toxic by both skin contact and inhalation. Glutaraldehyde has a short shelf-life <2 weeks, and is expensive. Formaldehyde is less expensive and has a much longer shelf-life if some methanol is added to inhibit polymerization to paraformaldehyde, but is much more volatile. Formaldehyde is also used as a gaseous sterilizing agent; in this case,it is prepared on-site by depolymerization of solid paraformaldehyde. Many vaccines, such as the original Salk polio vaccine, are sterilized with formaldehyde.