Dry heat sterilisation process control – Browne's tubes – Type 5

Browne's tubes Type 5 are chemical indicators designed for monitoring dry heat sterilization parameters. They allow verification that the required combination of process time and temperature has been achieved.

The tubes should be placed in various locations within the load, including near the product located in the area most difficult to access for the sterilising agent. This allows information to be obtained on the conditions prevailing in the controlled area of the chamber.

Browne Type 5 tubes – principle of operation

Each tube is made of borosilicate glass and is hermetically sealed at both ends. Inside there is approximately 200 µl of heat-sensitive liquid.

Upon reaching the required time and temperature parameters, the fluid changes colour from red to green. The change allows for an immediate visual assessment of the indicator's exposure to specific process conditions.

If the expected colour change does not occur, this means that the required parameters have not been met. The result should be interpreted in accordance with the manufacturer’s instructions and the procedure in force at the facility.

Parameters of the 7305AB indicator

Browne's tubes with a white spot, marked with a code 7305AB, are designed to control the following time and temperature combinations:

• 160°C for 120 minutes,
• 170°C for 65 minutes,
• 180°C for 35 minutes.

The dimensions of a single tube are 45 mm long and 5 mm in diameter.

Arrangement of the tubes in the batch

The sensors should be positioned in locations deemed to be the most difficult for hot air to reach. The number and layout of the sensors should be in accordance with the approved process control procedure.

Browne tubes are not a substitute for other sterilisation monitoring methods. They form part of the chemical monitoring process and should be used in conjunction with appropriate documentation and other monitoring methods required for the process in question.

Storing Browne tubes

The product should be stored in a cool, dry and shaded place, at a temperature of below 21°C. The manufacturer recommends storing in refrigeration conditions, if the current product instructions allow it.

Incorrect storage temperature may affect the properties of the indicator fluid and render the product unfit for use.

Key information

• chemical indicator for dry-heat sterilisation,
• Browne Type 5 tubes with a white spot,
• product code: 7305AB,
• colour change from red to green,
• control of the combination of time and temperature,
• dimensions of one tube: 45 × 5 mm,
• compliance with the requirements of ISO 11140-1,
• the pack contains 100 pieces.

The indicator result should be assessed in accordance with the manufacturer’s instructions. The colour change observed does not replace comprehensive monitoring, validation or documentation of the sterilisation process.