During installation, it is required that there must be a special exhaust pipe system, and the exhaust pipe material must be ethylene oxide which cannot be penetrated through, such as copper pipe. There shall be no combustibles or air inlets such as doors or windows in the building within 7.6m from the exhaust port; if the length of the vertical part of the exhaust pipe is more than 3m, a water collector must be installed, so as not to make the exhaust pipe sunken or looped to cause water gas accumulation or ice in winter to block the pipe; the exhaust pipe shall be led to the outdoor and reversed downward at the outlet to prevent water gas from remaining in the pipe wall or causing pipe wall block ; professional installation engineer must be employed and the installation must be carried out according to the requirements of ethylene oxide sterilizer manufacturer. For example, if ethylene oxide is discharged into the water, the whole discharge system (pipeline, water tank, etc.) must be sealed, otherwise a large number of hot ethylene oxide will overflow from the water and pollute the surrounding working environment.
Then the load goes through a long and complex sterilization cycle. Requirements of such a system are:
Accurate temperature control.
Availability of the control system.
Accurate pressure and vacuum control.
Easy displays of process phases
Dedicated customer recipes.
Auto batching release through tolerance tests.
Security interlocks between actuators.
Shut down strategies.
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During this cycle, accurate temperature control is important and a heating jacket is used. As the overall duration of this cycle is around 60 hours, high availability of the system is vital and system redundancy is required. Doubling sensors, actuators and controllers as well as changeover facilities on these components, helps to ensure the product is sterilized even on hardware or software failure.
After the doors have been shut down and sealed correctly, the cycle can be started either manually or automatically. If any problem with door sealing is detected the cycle is interlocked and cannot start. Security interlocks are also used between air and EtO valves.
Once the cycle is started, easy to use displays are required to show:
The actual phase of sterilization
All the key set points and tolerances as loaded by the recipe
All the key process values for the auto batch release facility
Control of vacuum and pressure is also required. Due to the toxic effect of EtO, water ring rotary pumps are used. The vacuum process needs to perform the emergency evacuation phase for a fast evacuation of gas.
The sterilization phases are:
Cycle start delay to enable the system to start in stable conditions
General cell temperature check
Initial vacuum phase
Leak rate test
DEC (Dynamic Environmental Conditioning)
EtO gas injection
Sterilization dwell time period under EtO
Post dwell vacuum level
Final air admission
Final chamber re-evacuation delay
During execution of these phases a batch report is generated. This report will include: tolerance checks, phase changes, alarms, events and critical process values. A key feature of the system is “auto batch” release. During the sterilization cycle if any abnormal condition occurs, the batch will be automatically stopped and condition(s) causing the stoppage will be identified. With this “auto batch” release facility operators do not have to wait until the end of the cycle and spend time going through the batch report to understand why it went wrong. With this feature, provided that batch is completed satisfactory it will be automatically forwarded to the degassing room without human check of tolerance, process values and alarms.