A strip chart - or the cycle printout that has replaced it on most new sterilizers - is the machine's own record of the run. It plots the chamber's temperature, and usually its pressure, against time. You read it for three things: whether the chamber reached the set temperature, whether the load held that temperature for the full exposure time, and whether the pressure and temperature moved together the way saturated steam requires. It is a process record, not proof that the load is sterile.
That last point is the one people get wrong. A clean-looking chart shows that the sterilizer did what it was programmed to do. It does not show that steam reached the instruments inside the packaging. That is a separate question, and it is answered by chemical and biological indicators rather than by the chart.
What does a sterilizer strip chart record?
The chart captures the physical, or mechanical, parameters of the cycle. The United States Centers for Disease Control and Prevention describes the same record in its sterilization guidance: the mechanical monitors for steam sterilization include "the daily assessment of cycle time and temperature by examining the temperature record chart (or computer printout) and an assessment of pressure via the pressure gauge."
| Element on the chart | What it shows | What a problem looks like |
|---|---|---|
| Temperature trace | The chamber temperature through the run | A short or rounded exposure phase, or a trace that never settles at the set point |
| Time axis | The length of the cycle and of each phase | Exposure shorter than the cycle's specified holding time |
| Pressure trace | The chamber pressure through the run | Pressure and temperature that do not track each other, which can indicate air or non-condensable gas in the chamber |
| Phase markers | The fill, heat-up, exposure, exhaust and dry stages | A phase that is missing, or a cycle that ends before the dry stage completes |
How do you read the exposure phase?
The exposure phase, sometimes called the plateau, is the flat section of the temperature trace where the chamber is held at its set point. Read it as a shape rather than a single number. A valid cycle holds the set temperature for the whole specified holding time, not just for one instant, and the exposure is counted from the point where the load reached temperature rather than from the start of the cycle.
Manufacturer guidance describes the same phases: Tuttnauer's sterilizer knowledge centre places the sterilization, or exposure, stage at 121 to 134 °C and 15 to 30 psi, and a Canadian college clinic's sterilization monitoring procedure notes that the printout is used to verify that the physical parameters required for sterilization were met for each load.
Why is a chart not proof that the load is sterile?
Because the chart measures the chamber, and sterility is a statement about the items inside the packaging. The CDC guideline is explicit that sterilization should be monitored "by using a combination of mechanical, chemical, and biological indicators", and that the mechanical monitors cover cycle time, temperature and pressure. Each type answers a different question.
| Monitor | What it is | What it tells you |
|---|---|---|
| Mechanical | The chart, printout, gauges and displays | The sterilizer ran the programmed parameters |
| Chemical | External and internal indicators, including autoclave tape and indicator strips | The package saw the conditions of the cycle, at the point where the indicator sits |
| Biological | A spore test, for steam using Geobacillus stearothermophilus | Whether the cycle actually killed a known resistant organism |
A passing chart therefore sits alongside, not instead of, a passing spore test. Tuttnauer's monitoring guidance puts the relationship plainly: "A passing cycle printout tells you the autoclave ran the programmed parameters. Indicators, biological challenges, and daily tests tell you whether those parameters reached the instruments inside the packaging."
How should the chart be kept?
As a record. The CDC guideline notes that sterilization records - mechanical, chemical and biological - should be retained for a period in compliance with standards and with state and federal regulations, and a Canadian clinic's retention period is set by its provincial guidance and college expectations rather than by the chart itself. In practice the chart or printout is filed with the load it belongs to, so that a load can be reconstructed later from the cycle record, the indicator result and, where it applies, the spore test. Clinics that want that set in one place can build it from the printable sterilization log sheet and log generators, which arrange the load, service and malfunction fields without an account.
Have a question about your own facility? Send it in and you will get a written answer specific to your setup, with the regulation or standard it is based on cited. Ask your compliance question.
Ordering for a clinic, lab or care home? Wholesale and multi-site ordering covers case pricing and account setup, and the B2B wholesale collection lists the lines stocked for institutional buyers.
Related reading
- How autoclave tape chemistry works: what the colour change actually measures
- Biological indicator monitoring in Canada vs the US: which sterilizer testing frequency applies
- CSA Z314 sterilizer testing after a major repair: how many biological indicators are required
Frequently Asked Questions
Is a strip chart the same as a cycle printout?
They record the same physical parameters. A strip chart is paper that plots temperature and usually pressure against time, and a printout is the digital version of the same data, which is why the CDC guidance treats the temperature record chart and the computer printout as one type of mechanical monitor.
What should I look for first on an autoclave chart?
The exposure phase. Check that the chamber reached its set temperature and held it for the full specified holding time, and that the pressure trace tracked the temperature rather than separating from it.
Does a good chart mean the instruments are sterile?
No. A chart shows the sterilizer ran the programmed cycle. Sterility assurance for the load comes from chemical indicators, which show the package saw the cycle conditions, and from the biological indicator spore test, which shows the cycle killed a resistant organism.
Why do temperature and pressure have to match?
Because saturated steam has a fixed relationship between pressure and temperature. If the two do not match, the chamber may contain air or non-condensable gas, which can reduce the steam's contact with the load even when the cycle looks normal.
How long should autoclave records be kept?
For the period required by the clinic's provincial guidance and college, which the CDC guideline frames as retention in compliance with standards and applicable regulations. The chart or printout is kept with the load record it belongs to.
CliniEco Medical holds Medical Device Establishment Licence MDEL #35334. This article summarises published national guidance from Canada and the United States for information only; it does not replace the sterilizer manufacturer's instructions, provincial infection prevention and control requirements, or the guidance of the relevant regulator for a specific practice setting.
Sources
- Centers for Disease Control and Prevention, Guideline for Disinfection and Sterilization in Healthcare Facilities - Sterilizing Practices
- Centers for Disease Control and Prevention, Guideline for Disinfection and Sterilization in Healthcare Facilities - Steam Sterilization
- Tuttnauer, Autoclave cycle, programs and time frames
- Tuttnauer, Autoclave sterilization monitoring: indicators, tests and daily protocols
- Cambrian College dental clinic, Sterilization Monitoring procedure (PDF)
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