SN 2002(02) - Dry heat (hot air) sterilizers

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January 2002

MANUFACTURER/SUPPLIER
Generic

PROBLEM
Many dry heat sterilizers do not have appropriate controls to provide assurance that sterilizing conditions have been achieved in the load. There is evidence that they are seldom maintained or are not subjected to periodic testing necessary to ensure that they are achieving sterilizing conditions consistently.

For the attention of:

Health Authorities (England) - Chief Executives
NHS Trusts (England) - Chief Executives
Social Services (England) - Directors
Primary Care Trusts (England) - Chief Executives

ACTION
1. Use a Sterilization Service Department (SSD) to reprocess reusable medical devices wherever possible

2. Take dry heat sterilizers out of use if they:

• do not have an automatic controller, or
• do not have door locks that prevent access to the load before a cycle is completed or if the cycle fails, or
•  are not maintained and tested weekly, quarterly and annually to verify that they are achieving sterilizing conditions.

3. Use steam sterilization in preference to dry heat.

DISTRIBUTION REQUIRED
Please bring this notice to the attention of all that need to know or be aware of it. This will include distribution by:

TRUSTS TO:

• Liaison Officers (for onward distribution)
• Control of Infection Teams
• Consultant Microbiologists
• EBME Departments
• Estates Departments
• Health and Safety Representatives
• Nurse Executive Directors
• Sterile Services Managers

HEALTH AUTHORITIES TO:

• Liaison Officers (for onward distribution)
• Chairs of Primary Care Groups
• Registration Inspection Units
• General Medical Practitioners
• General Dental Practitioners
• Practice Nurses
• Nursing homes
• Hospitals in the Independent Sector
• Health and Safety Representatives

SOCIAL SERVICES TO:

• Liaison Officers (for onward distribution)
• Registration Inspection Units
• Local Authority Environmental Health Officers

PRIMARY CARE TRUSTS TO:

• Liaison Officers (for onward distribution)
• Chiropodists
• Acupuncturists
• General Medical Practitioners
• General Dental Practitioners
• Practice Nurses
• Health and Safety Representatives

BACKGROUND
MDA frequently receives reports that dry heat sterilizers are not maintained, tested or used correctly and that they are seldom equipped with the necessary interlocks to ensure that an effective cycle is always completed before the operator can gain access to the load.

The success of a dry heat sterilization process can only be assured if the sterilizer is equipped with an effective controller and is maintained appropriately and tested periodically.

This is exemplified by a report that a general practitioner had used a dry heat sterilizer for many weeks before realising that it had not been switched on and that the loads, which consisted mainly of vaginal speculae, had not been sterilized during that time. Routing testing might have revealed the problem sooner. A recorder attached to the sterilizer would also have revealed the problem.

The supplier of the sterilizer should be able to provide service, maintenance and testing either directly or through a third party. There is anecdotal evidence that dry heat serilizers are often bought via mail order from organisations that seldom have technical back-up or maintenance provision. However, there is a number of independent contractors that should be able to provide these services.

The Annex to this notice provides further information.

ENQUIRIES
Enquiries to the MHRA should quote reference number 20000721.012-12

© Crown Copyright 2002

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Annex

Dry heat sterilization is an acceptable method of sterilization, provided that the load is exposed to one of the following minimum time/temperature relationships:

Sterilizing temperature band °C	Minimum holding time (minutes)
160 to 170	120
170 to 180	60
180 to 190	30

These are the holding times only. The total cycle time will be longer because it includes:

• the heating time, - the time required for every item of the load to reach the sterilizing temperature, which can vary considerably and depends on the composition of the load,
• the holding time, - the time for which the load must be held at the sterilizing temperature,
• the cooling time, - the time taken by the load to cool to a temperature at which the operator can remove items from the sterilizer safely.

To be certain that the sterilizer will produce sterilized devices consistently, it is imperative that:

• the selected temperature is achieved and maintained throughout the load for the duration of the relevant sterilizing time,
• appropriate safeguards operate to prevent normal access to a load during a cycle, or in the event of the cycle failing,

and that the sterilizer is:

• maintained in accordance with the manufacturer's instructions,
• tested periodically to check that safety features (e.g. door locks, overheat cutouts etc) and the automatic controller are functioning properly and the instrument readings are correct,
• not overloaded and it is loaded to ensure the effective circulation of air.

Each sterilizer should have a log book in which comprehensive records of all checks, tests, faults, repairs and modifications are made and retained.

The temperature must reach and remain within the sterilizing temperature band, throughout the sterilizing stage (holding time) and for not less than the required time specified in the table. To ensure this, the user should test the sterilizer at least once each week it is used, to verify that it is producing sterilizing conditions.

The test entails running a test load cycle and recording, or noting, the temperatures and corresponding times throughout the sterilizing stage and comparing them with the Master Temperature Record*. If any value is outside the specified limits, the load must not be used and the sterilizer should be taken out of service, re-tested and repaired if necessary. It should be returned to service only when it is known to be functioning correctly.

All observed values (e.g. from the temperature gauge and stop watch) obtained during the test should be noted and retained in the sterilizer log book. A recorder attached to the sterilizer simplifies the testing procedure.

The test may be performed with a load, provided there is a Master Temperature Record for that load. If the test is satisfactory, the load may be released for normal use.

*The Master Temperature Record should be the record of time and temperature values obtained by a competent test person, using calibrated test probes, when the sterilizer was known to be working correctly e.g. during works tests, validation etc.