The future of gas sterilization

Published by permission of Dan Mayworm .
Infection Control & Sterilization Technology Magazine - August, 1996

100% EtO processing:
Another alternative



An ongoing challenge to hospital CS departments is finding less costly alternatives to 12/88 EtO gas sterilization for the countless items that require low-temperature sterilization. There are drop-in replacements using HCFCs, new plasma systems, new technology in 100% EtO chamber systems, hydrogen peroxide, and perhaps coming soon, ozone systems. They all have their pluses and their minuses.

This article examines one solution to the problem, a 100% EtO system that uses proprietary gas cartridges placed in a plastic bag that becomes essentially the sterilzation chamber. This process is the result of attention to the clinical and safety issues involved and has validation data and usage history to support its claim of efficacy.

Something old. Something new.
Something borrowed. Something blue.


This old folklore, ensuring a bride’s happi-
ness, came to mind while thinking about a re-
cent visit to H.W. Andemen Products, Inc.
(Haw River, NC). It started with my article
on current sterilization technologies (ICST,
September 1995) that mentioned Andersen’s
100% EtO system. Most of the information on
this process came from talking to the sales
manager and reviewing company literature,
since I hadn’t seen the product in use for a
while. Knowing how interested our readers
are in anything new dealing with low-tem-
perature sterilization, I accepted an invita-
tion to visit the facilities when Andersen
Products wanted to show me their “new” ver-
sion of the “old” technology. I also found
something borrowed and something blue.

The “old” technology consisted of break-
ing open an ampoule containing 100% EtO
liquid and putting it into a container that was
loaded with packaged products for steriliza-
tion. The liquid EtO vaporized into a gas,
which then permeated the packages. The
“new” technology is based on the same prin-
ciple, though modernized.

For instance, the ampoule has been re-
placed with a single-dose, two-compartment
cartridge. One compartment contains the liq-
uid EtO and the other, a two-stage expansion
chamber. This construction provides a mar-
gin of safety in that it makes the cartridge
easy to activate and slows the release of EtO
from the cartridge. There is also a double
trigger-guard system to prevent accidental
activation of the cartridge.

To begin the process, you must first choose
the right size container for the load to be ster-
ilized. The company provides guidelines, but
trial and error will show that it doesn’t pay
to overload the bags. The containers are co-
extruded polyethylene/Surlyn@ bags that
come in three sizes; #6 has a volume of 60
liters (2.12 ft3), the #5 is 25 liters (.88 ft3) and
#4 is 15 liters (0.53 ft3). The packaged prod-
ucts to be sterilized are loaded into the prop-
er size bag. Matched to each size bag is the
appropriate size EtO cartridge, a Hu-
midichip@, a Dosimeter@, and a biological in-
dicator. (Figure 1).

These are all placed into the bag, which is
then heat sealed and the cartridge activated.

The Humidichip is a moistened blotter
that evaporates enough moisture vapor at
the chamber temperature to maintain 60%
relative humidity within the bag. Humidity
is an important factor in EtO sterilization,
therefore, care should be taken to precondi-
tion the load prior to sterilization. Highly
desiccated or absorbent loads might cause a
steriliiation problem.

The Dosimeter is a proprietary chemical
integrator providing visual assurance that
conditions for sterilization have been met.
Any biological indicator appropriate for EtO
sterilization (B. subtilis) can he used, either
self-contained BIs or spore strips.

The system “borrows” the name steriliz-
er for a modular chamber that has controls
bolted to it for temperature, exhaust, and
timingmechanisms. The chamber is available
in 6,10,24 and 33 ft3 models as standard but
can also be custom-designed to fit the user‘s
load capacity and equipment requirements.
After activating the cartridge, the bag is
placed into the chamber where it remains in
a 50°C controlled temperature environment.
The gas slowly elutes through the bag and is
then exhausted from the chamber. Steriliza-
tion and aeration is accomplished in 16 hours.
If at any time the temperature deviates from
50”C, the operator is notified both visually
with a flashing light and aurally with a warn-
ing bell.

That’s all there is to it. The secret is in the
controls that are bolted to the chamber and
the safety features incorporated into its de-
sign. For example, operators must input their
discrete code number. Then a fast five-
minute purge cycle evacuates any residual
gas in the chamber before the door will open.
The door can only he left open for three min-
utes, ample time to remove a completed load
andor place a new one into the sterilizer.