April 6, 2020
A Look At Gas Sterilization
By Michael D. Shaw
With COVID-19 on the minds of everyone, thoughts naturally flow toward infection control. A classical method of infection control is sterilization, defined as “[A] process that destroys or eliminates all forms of microbial life and is carried out in health-care facilities by physical or chemical methods.” A step down from this is so-called high-level disinfection, defined as “[T]he complete elimination of all microorganisms in or on an instrument, except for small numbers of bacterial spores.”
These concepts are clearly presented in this table (refer to second page of linked article). Most readers are familiar with the process of steam sterilization, whereby three parameters are important: time, temperature, and pressure. In general, the conditions are set to 121° C (249.8° F) for at least 30 minutes by using saturated steam under at least 15 psi (103.4 kPa) of pressure. Various sterilizer designs allow for modification of those specifications.
Steam sterilization is ideal for devices that can withstand the heat and pressure, such as stainless steel instruments, glassware, and reusable gloves. However, there are scores of items that cannot take these conditions, including flexible endoscopes, catheters, equipment with integrated electronics, stents, and wound care dressings. For these, gas sterilization is used. While ethylene oxide is the most common gas used for this purpose, others include ozone, chlorine dioxide, formaldehyde, and nitrogen dioxide.
It is noted that any substance that can kill pathogens will be harmful to humans, as well. That’s why it is standard procedure to monitor the air around sterilization and disinfection equipment to ensure that no gas has escaped from these processes.
Another popular low-temperature sterilization method utilizes hydrogen peroxide gas plasma. “Plasma” is considered a fourth state of matter beyond solid, liquid, and gas. Plasma is a cloud of protons, neutrons, and electrons where all the electrons have come loose from their respective molecules and atoms, giving the plasma the ability to act as a whole rather than as a bunch of atoms. This technology utilizes hydrogen peroxide and takes advantage of the synergism between its gas and plasma states to rapidly destroy microorganisms.
Hydrogen peroxide can be deployed in another manner for infection control purposes, as vaporized hydrogen peroxide. In practice, liquid hydrogen peroxide is vaporized into the air or chamber at a pre-programmed concentration, typically ranging from 140 to 1400 parts-per-million. This vapor is circulated in the space for a set period of time, and then the vapor is extracted back into the generator, where it is broken down into harmless oxygen and water.
Technically, a vapor is not necessarily the same as a gas. Rather, it is a substance in the gas phase at a temperature lower than its critical temperature. As such, a vapor can be condensed to a liquid by increasing the pressure on it without reducing the temperature. Nonetheless, many people in the field refer to vaporized hydrogen peroxide and hydrogen peroxide gas plasma as “gas sterilization” methods.
A very interesting use of vaporized hydrogen peroxide has been introduced by Battelle. Battelle calls it the Critical Care Decontamination System. Now, N95 masks can be processed up to 20 times with this new machine. And, this methodology is being tested to see if it might work on such things as ventilator components.
In operation, the machine uses vaporized hydrogen peroxide to treat the respirator masks for 2.5 hours. The decontamination process also works for SARS-CoV-2.
“The Battelle team mobilized to begin acquiring parts and developing manufacturing processes to deploy systems to help those on the frontline who need essential protective equipment,” said Matt Vaughan, Battelle’s Contract Research President. “We are building the next units and are in discussions with health officials across the country to determine where to best place them.”
How’s that for good news in these strange and difficult times?