In addition to the high temperature, steam must be
saturated so that it will quickly release heat through
condensation when it comes into contact with a cool
object. Sterilization will not occur unless all air is
eliminated from the chamber at the beginning of the
process and periodically throughout sterilization. The
packaging of supplies and loading of the sterilizer must
be done so that steam comes in contact with all areas or
surfaces of the items being sterilized.
Flash sterilization is defined as the sterilization of
unwrapped items in a gravity displacement or
prevacuum sterilizer with recommended minimum
exposure times and temperatures. Steam sterilization
by this unwrapped method is not recommended. It
should be used only for emergency sterilization.
Types of Steam Sterilizers
A steam sterilizer, also know as an autoclave, is
a pressure-type vessel with a door or cover, valves to
control the entry and exit of steam and air, and
monitoring devices to allow the operator to observe
conditions inside. It is designed to hold items and
allow steam under pressure to penetrate these items.
Steam sterilizers are available in many sizes, ranging
from portable countertop to the fixed room-size
sterilizer. Two of the most common types of steam
sterilizers used in the Navy are the gravity
displacement and prevacuum sterilizers.
sterilizer is loaded and the door is closed as shown in
figure 10-10, steam is admitted through an inlet and the
sterilization process begins. A typical standard for
steam sterilization is achieved at 250°F or 121°C after
20 to 30 minutes at 15 psi. It is important to refer to the
manufacturers instructions for operation, since
exposure times can vary according to the design of the
You should observe the following precautions
when loading the sterilizer chamber:
Do not overload. The passage of steam from the
top of the chamber to the bottom should not be
Place all packages on edges, with large packs at
the bottom of the chamber, and small packages
in an upper layer crosswise to the lower layer.
This allows free passage of steam.
If mixed loads of metal items and linen are
sterilized together, the linen is placed on the
upper shelf and the metal items on the lower.
Articles that require the same amount of time
and the same final steps should be sterilized
Enclosed fluids are sterilized separately because
the pressure must be slowly released.
Load all packages at the same time when you are
ready to sterilize.
A standard operation chart for the correct exposure
period of all supplies should be prepared and posted for
easy daily reference. It is important to note that
sterilizing conditions are based on temperature rather
than on pressure. Effective steam sterilization and
exposure time are measured from the moment the
thermometer in the discharge line indicates the desired
preset temperature. The pressure inside the sterilizer is
not an indication of positive sterilization because other
factors determine the pressure inside the sterilizer.
Pressure merely maintains temperature.
PREVACUUM STEAM STERILIZER.The
prevacuum steam sterilizer (fig. 10-11) was designed
to help overcome the trapping of air in the chamber.
Trapping of air is one of the greatest dangers
encountered when using saturated steam under gravity
cycles. When errors are made by improperly
packaging items or overloading the sterilizer chamber,
cool air pockets may form resulting in items not being
The speed and efficiency of the steam
sterilizer may be improved by removing air from the
chamber with a powerful pump, creating a nearly
perfect vacuum before steam is introduced into the
chamber. This procedure allows fast and more positive
heat to penetrate the entire sterilizer load. The
improved sterilizer is referred to as the prevacuum
Full heating of the loads is faster in the prevacuum
sterilizer than in the gravity displacement sterilizer.
For example, wrapped instruments can be sterilized at
270°F (131°C) after 4 minutes exposure in a
prevacuum steam sterilizer. Consult the manu-
facturers instructions for specific details on operation
and user maintenance information.
The Bowie-Dick type test was developed for
prevacuum sterilizers to determine if the air has been
removed from the chamber during the prevacuum
stage. Air must be removed so that steam can penetrate
the load instantaneously. It must be understood that
this is not a test for adequate exposure to heat in terms
of time-at-temperature. A commercially prepared
Bowie-Dick type test can be used by carefully reading
and following the manufacturers instructions. All