M4/21 - Autoclaves

Autoclave incident resulting in release of biological waste not fully decontaminated


  • Heads of department must ensure that the actions listed below have been implemented.
  • Supervisors must ensure their workers are made aware of the information below, including any changes to the Standard Operating Procedures (SOP). Where necessary, retraining must be given and documented in a training record. 
  • Autoclave operatives must ensure they work to the specified Standard Operating Procedures.
  • Waste producers must be informed, instructed and trained on correct waste disposal routes and be aware of the consequences of the inappropriate disposal of their waste.
  • Departmental safety officer/biological safety officer should support the head of department and supervisors by overseeing the actions listed below, with input for individuals involved in operating the autoclaves. A report must be made to the departmental safety advisory committee.

Legal requirements for inactivation of biological waste

We are required, by law, to inactivate biological waste prior to disposal. In Containment Level 1 and 2 laboratories, this may be achieved using disinfectant (according to the manufacturer’s instructions) for liquid waste and autoclaving for plastic ware.

Autoclaves require regular examination and testing by a competent person under a written scheme of examination, as well as an annual 12-point validation for each load type by a competent person to ensure the load achieves the required sterilisation. In between these 12-month validations, data loggers (either printout or digital) must be checked and stored. Where there has been a failure in the cycle to achieve the specified conditions, the waste must be re-autoclaved or safely transferred to another autoclave for treatment.


Overview of incidents involving autoclaves

  1. Waste was not held at the correct temperature for sufficient time to achieve sterilisation. This was not noticed for a number of days leading to waste being disposed of that had not been fully inactivated. Fortunately all the waste was from low risk class 1 / hazard group 1 work.

    Key findings: The engineer had changed the cycle conditions for servicing; these were not returned to the correct settings afterwards and therefore did not indicate a failure. This was spotted due to the printouts not being as long as normal.

  2. Waste in a yellow clinical waste bag was autoclaved, which damaged the integrity of the bag. The damaged bag was still placed out for collection, which lead to the spillage of the contents when the bag was collected. 

    Key findings: Where clinical waste is required to be autoclaved prior to disposal, the SOP should detail how this must be undertaken. This information should be reiterated in risk assessments and waste disposal policies.

  3. Waste removed from an autoclave before the cycle was run.

    Key findings: Fortunately in this case, the waste was retrieved before being collected by the waste contractor.

Other incidents have included:

  • Inappropriate and unsafe disposal of chemicals into autoclave bags causing a fire.
  • Disposal of gas canisters in an autoclave, which was fortunately spotted by the autoclave operative and not autoclaved.
  • At higher temperatures of inactivation, sharps bins being affected leading to lids coming off or sharps protruding through the sides.

 Actions required by departments

 As a consequence of the recent incidents departments are required to take the following actions: 

  • Ensure an SOP is in place for use of the autoclave(s).
    • Where an SOP is already in place, it must be reviewed to see if any amendments are required, taking into account the above information;
  • Ensure that training is given to all operatives on how to run the autoclave(s).
    • This must include checking the cycle run and not just looking for error codes;
  • Ensure that after an engineer has attended the autoclave (for whatever reason) that all discard cycles are returned to expected conditions.

Guidance on creating a Standard Operating Procedure for autoclaving.

The Standard Operating Procedure for autoclaving should specify as a minimum: 

  • The type of waste to be autoclaved, eg cultures and media, sharps, pipettes, other disposable and reusable articles, gloves and laboratory coats, paper towels and tissues.
  • The type of waste not to be autoclaved.
  • The containers that are to be used, eg for sharps.
  • The required sterilising cycle, eg temperature and time settings, validated for the load type.
  • Whether biological or chemical indicators are to be used and their location in the load.
  • The checks to be made and recorded by users, eg cycle print outs.
  • The loading and unloading procedure.
  • The subsequent handling and disposal of the autoclaved waste.
  • The procedure in the event of a malfunction or failure.
  • The maintenance regime (routine servicing, repair, examination and testing.) This should also detail the requirements in examination of Pressure Systems Safety Regulations 2000 8(1).
  • What personal protective equipment is required.
  • What are the hazards, ie heat, steam, electrical, slips, manual handling etc?

Standard conditions for disposal cycles are:

  • 121-125oC for at least 15 minutes;
  • 126-130oC for at least 10 minutes;
  • 134-138oC for at least 3 minutes.

However, 12-point validations, for example loads (ie plastics, mixed waste, liquid, lab coats, soil etc) should be performed annually to determine how long the temperature should be held for to ensure the entire load reaches minimum conditions.

Training records must be maintained for all individuals operating an autoclave irrespective of whether the autoclave is used for waste or for sterilising clean items. Ideally a document should be in place which details the training an individual must receive before using an autoclave, the level of supervision required and for how long and how frequently competency should be checked. This enables a consistent approach to the training provided, especially if key staff leave the post. Simply reading the Standard Operating Procedure is not a sufficient level of training. This training document should also provide detail on why an autoclave is used and how it works to inactive biological agents or this information can be included in the Standard Operating Procedure.
Existing examples of Standard Operating Procedures

There are some good examples of Standard Operating Procedures for autoclaves that are already in place around the University and these typically have the following details:

  • reference number, version number, title, sign off, date and review date;
  • introduction;
  • scope;
  • responsibilities;
  • safety / hazards;
  • what to do in an emergency, ie burns / leak of steam / setting off fire alarms;
  • operation summary - may include collection of waste, loading, unloading and disposal after autoclaving;
  • storage of cycle records;
  • aborting cycles;
  • cycle options;
  • common error messages;
  • maintenance (cleaning water sensors, draining etc);
  • breakdowns / reporting problems;
  • maintenance record sheet including error codes;
  • training record sheet.

The good examples of Standard Operating Procedures include colour photos or pictures. These documents are far more engaging and can be useful for showing what the text is trying to describe.