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When you open your sterilizer door, the last thing you want to find are wet packs, which are packs in which condensation has collected and pooled on the instruments, providing a pathway for organism migration into the pack. OR managers and personnel have been grappling with this problem for years. In this article, I'll discuss the factors that may cause wet packs and discuss some simple steps you and your staff can take to prevent them.
It all starts with steam
Ensuring excellent steam quality is the first step for preventing wet packs. You must first understand how steam sterilization works. Here's a quick review (for more on steam sterilization, see my February 2001 article, "A Primer on Steam Sterilization"):
Water can exist as a solid, liquid or gas, depending upon the temperature of the water. Water below a temperature of 0o C (32o F) will turn to a solid (ice). Water above 100o C (212o F) will turn to a gas (steam). It takes energy, in the form of heat, to convert water from its liquid to its gas state. On reaching 100o C, it takes considerably more energy to convert the water to steam. At this point both the water and the steam are at the same temperature (this is called the saturation temperature) but the steam has considerably more energy. This difference in energy is called the latent heat of vaporization. When a cold object (such as a surgical instrument) is placed in this steam, the steam gives up some of its latent heat to the object in the form of condensation.
A temperature of 100o C is insufficient to kill most microorganisms, so a sterilizer uses a sealed pressure vessel to increase the saturation temperature to 121o C or higher. At this temperature, liquid water is 785 times more dense than the steam. Therefore, during condensation, the volume occupied by the steam decreases by a factor of 785, creating a vacuum that is immediately filled by the steam that did not condense. This constant replenishment of steam at the site of condensation explains steam's excellent penetration capabilities-the vacuum continually pulls the steam into the package.
It's not enough to have hot steam-you also have to have high-quality steam, which means steam that is relatively dry. Steam quality is defined as the mass of steam divided by the mass of liquid in the steam plus the mass of steam.
Steam quality =
It all starts with steam
Ensuring excellent steam quality is the first step for preventing wet packs. You must first understand how steam sterilization works. Here's a quick review (for more on steam sterilization, see my February 2001 article, "A Primer on Steam Sterilization"):Water can exist as a solid, liquid or gas, depending upon the temperature of the water. Water below a temperature of 0o C (32o F) will turn to a solid (ice). Water above 100o C (212o F) will turn to a gas (steam). It takes energy, in the form of heat, to convert water from its liquid to its gas state. On reaching 100o C, it takes considerably more energy to convert the water to steam. At this point both the water and the steam are at the same temperature (this is called the saturation temperature) but the steam has considerably more energy. This difference in energy is called the latent heat of vaporization. When a cold object (such as a surgical instrument) is placed in this steam, the steam gives up some of its latent heat to the object in the form of condensation.
A temperature of 100o C is insufficient to kill most microorganisms, so a sterilizer uses a sealed pressure vessel to increase the saturation temperature to 121o C or higher. At this temperature, liquid water is 785 times more dense than the steam. Therefore, during condensation, the volume occupied by the steam decreases by a factor of 785, creating a vacuum that is immediately filled by the steam that did not condense. This constant replenishment of steam at the site of condensation explains steam's excellent penetration capabilities-the vacuum continually pulls the steam into the package.
It's not enough to have hot steam-you also have to have high-quality steam, which means steam that is relatively dry. Steam quality is defined as the mass of steam divided by the mass of liquid in the steam plus the mass of steam.
Steam quality =
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