TL;DR
Pressure drop during the EtO dwell phase usually means a door seal failure, a valve seat leak, or a chamber penetration fitting loose. Perform a nitrogen leak test before restarting with EtO.
What you might see
- chamber pressure declining during the EtO dwell phase
- cycle abort from dwell pressure falling below limit
- EtO gas consumption higher than normal
- EtO monitor alarm near the sterilizer door during dwell
Likely causes
Chamber door seal cracked or permanently set, allowing EtO to escape
Gas inlet or exhaust valve seat worn or particle-contaminated, allowing back-leak
Chamber penetration fitting loose from thermal cycling
Safety valve set pressure drifted below the dwell pressure
Required tools
- Dry nitrogen supply
- Calibrated pressure gauge
- Soap solution or snoop-type leak detector
- Replacement door seal
- EtO fixed-area gas monitor
Safety first
- EtO is toxic, carcinogenic, and flammable. Never work on the chamber unless the fixed EtO monitor confirms gas-safe conditions below the permissible exposure limit.
- Use nitrogen for leak testing. Never use EtO gas to perform a leak search.
- Wear EtO-rated respiratory protection during any post-cycle chamber inspection until gas-safe status is verified.
Procedure
- 1
Do not reopen the sterilizer until the EtO purge cycle is complete and the fixed EtO monitor reads below the permissible exposure limit.[1]
- 2
After gas-safe status is confirmed, pressurize the chamber with dry nitrogen to the dwell pressure level.
- 3
Monitor the nitrogen pressure over 30 minutes. A rate of decay above the system specification confirms a real leak.[1]
- 4
Apply a soap solution or a snoop-type leak detection fluid to the door seal perimeter, all valve stem packing areas, and all chamber penetration fittings.
- 5
Mark each leak location. Vent the nitrogen before beginning any repair.
- 6
Replace the door seal if leaking. Tighten or reseal any loose penetration fitting. Replace any valve seat that passes nitrogen.
- 7
Repeat the nitrogen pressure hold test after repairs before reloading with EtO.
Sources
Steris Steris EtO Sterilizer EtO Sterilizer general technical documentation, Steris
Steris EtO sterilizer general chamber integrity and leak test procedures (general)
More guides for Steris Steris EtO Sterilizer
How to fix a sterilization cycle abort from a humidity fault on a Steris EtO Sterilizer
Humidity faults abort the cycle because EtO sterilization requires a relative humidity above 30% to kill spores. Check the humidification system and chamber humidity sensor calibration.
How to fix EtO residual levels above specification on a Steris EtO Sterilizer
High EtO residuals on the product are usually insufficient aeration time, an aeration chamber temperature below set-point, or a product load configuration that blocks airflow. Extend aeration and verify chamber temperature first.
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