3M Attest Technical Information
3M™ Attest™ Steam
Chemical Integrator
Technical Information
STEAM
Dynamics of Steam Sterilization
Steam sterilization has been used for over 100 years. Decades of research have
shown that the ecacy of a steam sterilization process is the function of three
basic parameters: time, temperature and the presence of saturated steam. All
three are critical process variables for eective steam sterilization.
The importance of saturated steam is demonstrated when dry heat sterilization
is compared with steam sterilization. The use of steam allows faster sterilization
than dry heat. For example, dry heat sterilization requires a sterilization time of
60 minutes at 320°F (160°C), while steam sterilization at the same temperature
would take less than a minute.1 Clearly, steam quickens the kill time of living
organisms by many orders of magnitude and is generally preferable to dry heat.
2
3M™ Attest™ Steam Chemical Integrator Technical Information
Once a saturated steam environment is obtained, the
independent variables of time and temperature can be
determined by the following formula:
t = Fo × 10
Where
t = time for 100% kill at temperature T
(2 50-T )/Z
2
T = processing temperature (0°F)
Fo = kill time for Geobacillus
stearothermophilus with a z-value of
18°F (10°C) and D-value of 1 minute at 250˚F
(121˚C)
z = rise in temperature required to increase
the rate of kill by a factor of 10 (usually
about 18˚F (10˚C))
Interpretation of this formula shows that the
relationship of processing time (t) versus temperature
(T) can be plotted as a logarithmic function. Expressed
dierently, it means that a small uctuation in the
temperature results in a large change in the actual
processing time required for 100% kill. Figure 1 shows
the thermal death time at dierent temperatures for
1 million live spores of Geobacillus stearothermophilus.3
This curve can be expressed mathematically by the
following formula which shows that it takes 12 minutes
to kill 1 million living spores in a 250°F (121°C) steam
sterilization cycle.
t = (12)10
(250-T)/18
Where
Fo = 12 min for G. stearothermophilus
z = 18°F (10°C) for G. stearothermophilus
In order to show the high sensitivity of kill time to
temperature, the above formula can be solved for
247°F (119°C).
t = (12)10
t = (12)10
(250-247)/18
(0.167)
= (12)(1.47)
t = 17.6 minutes
In theory, therefore, if the inside temperature of a
sterilizer were actually operating at 247°F (119°C)
instead of 250°F (121°C), a time of 17.6 minutes
would be required to kill the 1 million spores of G.
stearothermophilus at 247°F (119°C) versus the 12
minutes needed to kill the spores at 250°F (121°C).
This interdependence of time and temperature (in
saturated steam) is an important relationship which
should be understood by all personnel responsible
for providing sterility assurance for steam sterilized
items. Consider the ramications if a sterilizer was
inadvertently set at a processing temperature at
247°F (119°C) instead of 250°F (121°C). Or, if the load
was processed at 247°F (119°C) as a result of a minor
malfunction of the sterilizer (e.g., air pocket or small air
leak), a slight calibration error or a natural drift in the
temperature monitoring system, incorrect loading or
packaging.
Because even small decreases in temperature during
steam sterilization may signicantly increase the time
necessary for assurance of sterility, an accurate means
of monitoring internal sterilizer and pack conditions
are essential.
3M™ Attest™ Steam Chemical Integrator Technical Information
Integrating Indicator vs. Biological Death Curve
3
100.00
10.0
1.0
Time (min.)
Theoretical G. stearothermophilus
Thermal Death Time
0.1
118 122 126 130 134 138
Three Typical Stated Values
™
Attest™ Steam
for 3M
Chemical Integrators
Temp (°C)
Pack and Load Control
The dynamics of steam demonstrate the need for
accurate monitoring of internal sterilization conditions.
Pack control is the use of chemical indicators for the
internal monitoring of packs, trays, containers, and peel
pouches. Internal chemical indicators should be used
inside each type of packaging to address the potential
for interference with proper steam sterilization
conditions in all of these types of packaging.
Several problems can occur in the packaging and
loading of individual packs that can inhibit air removal
and steam penetration which leads to a lower
temperature. Packing problems include:
• Incorrect packaging or container system chosen
for the cycle parameters;
• Incorrect preparation of the container for use
(i.e., lters and valves or inappropriate bottom tray);
• Placing a folded peel pouch inside another
peel pouch;
• Placing a peel pouch inside of an instrument tray
or container system (if not recommended by the
manufacturer);
• Preparing textile packs that are too dense to sterilize
in the cycle parameters chosen;
4,5,6
Figure 1. Graph comparing three
typical Stated Values of 3M™ Attest™
Steam Chemical Integrators with the
theoretical death curve of Geobacillus
stearothermophilus spores.
• Over loading the individual packaging or container
system chosen (an over weight package).
Loading problems include:
• Stacking container systems (if not recommended
by the manufacturer);
• Laying peel pouches at or on top of each other
instead of on edge;
• Improperly placing peel pouches on edge (plastic
sides not facing all in one direction);
• Turning instrument trays on edge;
• Laying fabric packs or basins at;
• Placing packages too close to each other impeding
air removal and sterilant penetration around and
through the load;
• Rigid containers systems loaded above wrapped
or pouched items.
Malfunctioning equipment can also result in
insucient sterilization conditions inside of
packaging as the result of:
• Incomplete air removal;
• Inadequate cycle temperature;
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