Chemical Indicators for Steam Sterilization

Chemical indicators for autoclaves and steam sterilizers play a critical role in sterility assurance programs. There are many types of chemical indicators, such as bowie dick test packs and chemical indicator strips.

All chemical indicators are designed to respond to physical conditions inside the sterilizing chamber. This validates that an autoclave or steam sterilizer is working properly. It also verifies that it met the conditions for sterilization to occur.

Standards for Chemical Indicators

The International Organization for Standardization (ISO) issues many standards for sterilization processes. Chemical indicators must adhere to these manufacturing and application standards, and guidance documents.

ISO 11140-1:2014 is identical to:

  • BS EN ISO 11140-1:2009
  • ANSI/AAMI/ISO 11140-1:2014

ISO 11140-1:2014 replaces previous standards:

  • EN867-1
  • ANSI/AAMI ST60:1996

The most current standard is ISO 11140-1:2014. It defines 6 different types of chemical indicators for sterilization.

6 ISO Types of Chemical Indicators for Steam Sterilization

ISO 11140-1:2014 classifies chemical indicators for autoclaves and sterilizers as follows:

  • Type 1: Process Indicators
  • Type 2: Specific-Use Indicators
  • Type 3: Single-Variable Indicators
  • Type 4: Multi-Variable indicators
  • Type 5: Integrating Indicators (Integrators)
  • Type 6: Emulating Indicators (Cycle Verification Indicators)

The types are not ranked by level of importance. Type 1 is not better than type 6. Each type simply denotes performance characteristics and intended use of chemical indicators.

ISO 11140-1:2014 section 4.1
“The classification structure used is solely to denote the characteristics and intended use of each type of indicator when used as defined by the manufacturer. This classification has no hierarchical significance.”

Since performance requirements are distinct, chemical indicators should only comply with one type. This chart summarizes the different ISO types of chemical indicators. It also provides examples of applications and STERIS Life Sciences products available for each type. Use it to help choose the correct chemical indicator for monitoring specific sterilization processes.

6 ISO Types of Chemical Indicators for Steam Sterilization

Type 1: ProcessOne or more critical variables in the sterilization process

The unit has been directly exposed to the sterilization process

Autoclave tape or chemicalindicator strips

Located inside or attached to the outside of packs

Provide visual confirmation of exposure to sterilization process

VERIFY Valueline Class 1 Steam Chemical Indicator (PCC009)

Steam Indicator Tape (260010)

Type 2: Specific-UseDefined in relevant sterilization standards for specific test procedureBowie-Dick test packs

Test air removal in a prevacuum steam sterilization cycle

Steraffirm® Bowie-Dick Test Pack (EQC003)

VERIFY Bowie-Dick Test Packs (EQC009, EQC010)

Daily Air Removal Test–DART® (NB113, NB215)

VERIFY Bowie-Dick Test Card (S3095)

Type 3: Single-VariableOne critical variable in the sterilization process

Exposure to a sterilization process at a stated value (SV) of the variable

Chemical pellet

Melts at a specified temperature

Demonstrates the steam sterilization process has achieved a specified temperature

Not currently available
Type 4: Multi-VariableTwo or more critical variables in the sterilization process

Exposure to a sterilization cycle at stated values (SVs) of the variables

Chemical indicator tubes

Change color only when exposed to a given temperature for a specified time in a steam sterilization application

Steraffirm Sterilizer Control Tube
Steam at 121°C/250°F for:
-15 minutes (PCC024)
-12 minutes (PCC025)
Type 5: Integrating (Integrators)All critical variables in the sterilization process

Stated values (SVs) meet or exceed performance requirements in the ISO 11138 series for biological indicators

Moving front indicators

Respond to all critical process parameters

VERIFY Steam Integrating Indicator (PCC065B, PCC065, PCC064)
Type 6: Emulating (Cycle Verification)All critical variables for specified sterilization cycles

Stated values (SVs) are generated from the critical variables of the specified sterilization process

Cycle-specific indicators

Typically placed in the pack, pouch or container

Respond to all critical process parameters for a specified sterilization cycle

Steraffirm Steam Class 6 Emulating Indicators
-121°C/ 250° for 15 minutes (PCC012)
Critical Variables in Steam Sterilization    Time    Temperature    Steam