8 Preparing for sterilization
Thermo Scientific
41
50112712_082007_GB
Diagram 1: Sterilization cycle at 134 °C / 304 kPa with fractionated prevacuum
e.g. P
1
Instruments (load up to 8.5 kg),
P
2
Textiles 1 (load up to 8 kg), Textiles 2 (load up to 7.5 kg)
Process description:
t
bv1
-t
bd1
:
The chamber is evacuated to more than 90 % up to 7 kPa. The double
wall is preheated to sterilizing temperature. The load still contains “thin
residual air”.
t
bd1
-t
bd2
:
The steam penetrates from all sides up to 170 kPa, “compressing” the
residual air within the load. The steam condenses in the marginal zones
as the heat is released to the cooler load.
t
bv2
-t
bd3
:
The chamber pressure is reduced (7 kPa) and released (170 kPa) sev-
eral times. As a result, the condensate inside the chamber evaporates
and another portion of the residual air is evacuated from the chamber.
At the same time, the double wall is heated.
t
bd3
-t
bp
:
The sterilizing chamber is heated by inflowing steam until the target
temperature is reached (304 kPa). Saturated steam is forming inside
the
chamber.
t
bp
-t
eh
:
The sterilizing chamber is completely filled with saturated steam. Micro-
organisms are destroyed by the action of moist heat.
t
eh
-t
bt
:
The chamber pressure is released until 120 kPa is reached, and the
remaining condensate is evacuated. Then the steam is siphoned from
the chamber, causing the pressure to drop and therefore the remaining
condensate to evaporate.
t
bt
-t
et
:
When 20 kPa are reached, the drying phase starts. Throughout the
drying phase, the double wall is maintained at sterilizing temperature.
t
et
-t
ez
:
The sterilizing chamber is aerated via the sterile air filter.
Sterilization cycle at 134 °C/304 kPa with fractionated prevacuum
0
20
40
60
80
100
120
140
160
180
200
220
240
260
280
300
320
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
Time (min)
Pressure (kPa)
pressure
Atmospheric pressure
t
bv1
t
bd1
t
bv2
t
bd2
t
bv3
t
bd3
t
bp
t
eh
t
bt
t
et
t
bv1
= Beginning of the first evacuation phase
t
bd1
= Beginning of the first steam entry phase
t
bv2
= Beginning of the second evacuation phase
t
bd2
= Beginning of the second steam entry phase
t
bv3
= Beginning of the third evacuation phase
t
bd3
= Beginning of the third steam entry phase
t
bp
= Beginning of the holding phase
t
eh
= End of the holding phase
t
bt
= Beginning of the drying phase
t
et
= End of the drying phase
