Ventilation, air changes and fallow time

As I write, the most important question on most dentists minds is ‘when can we change the fallow time?’

Two new pieces of information from NHS Scotland were published a little over a week ago that may give us a clue about what the guidance from the Chief Dental Officers may look like when it comes.

The first of these is an SBAR (Situation, Background, Assessment, Recommendation) report from a short life working group that was established to review and make recommendations for remobilisation, development of guidance and other related activities such as training; specifically in relation to all aspects of ventilation. Their task was to look at what part ventilation may play in the management of the ongoing COVID-19 situation as it relates to dental practices.

The group also explored the contribution that different factors play in mitigating the associated risk from Aerosol Generating Procedures (AGPs). It included a rapid review of the literature, a critical appraisal of the fundamental requirements for ventilation as a control strategy along with other mitigating requirements, and the modelling of the AGPs with reference to the site and surrounding area.

The document examines the current evidence base and is not intended as specific formal guidance in itself, rather it is intended to provide recommendations to help inform future policy and the development of guidance. It is expected that the Chief Dental Officers will use the findings when the Standard Operating Procedures are updated.

The SBAR document was posted on 4th August, is 82 pages long and has not received a universally enthusiastic response due to many perceived contradictions. This is to be expected though given the lack of definitive knowledge about many aspects of the SARS-CoV-2 virus and given the fact that different papers often reach different and often contradictory conclusions, thereby further reinforcing the view that much is still unknown.

Summary of findings

• The report stresses that the fallow time remains one hour until official, national guidance changes.
• There inevitably needs to be a compromise between risk minimisation and practicability, bearing in mind the risks of transmission between individuals can be mitigated but cannot be removed altogether.
  Ventilation, air change and fallow time – a summary 18.8.20
• Social distancing should be observed in reception and waiting areas, with a minimum distance of two metres maintained between patients. Patients should be encouraged to arrive at their exact appointment time to avoid spending longer than necessary in the waiting room. Patients should be required to wear a face covering when in these areas.
• All team members should wear a fluid-resistant mask at all times in the practice.
• There is no requirement for fallow time following a non-AGP treatment. Apolline note: Our view is that there is no such thing as a non-AGP appointment because breathing and talking and all dental procedures usually referred to as non-AGP do create an aerosol, just not as much aerosol as dental procedures known to produce high volumes of aerosol. We therefore recommend that the surgery is thoroughly cleaned a minimum of 10 minutes after the appointment has finished and the patient has left. The period between the patient leaving and cleaning starting should be used for taking the instruments to the decontamination room, doffing PPE, and writing up patient records. Thorough cleaning should then be undertaken as
  the last process before the next patient comes in.
• You need to know how many air changes an hour your ventilation system is achieving in all
  rooms in the practice and especially in all surgeries.
• The ventilation system should be set to achieve the maximum amount of fresh air and air
  changes it is able to provide.
• If there is no mechanical or natural (large enough open window) ventilation in a surgery, then
  AGPs must not be undertaken in that room. This would be a breach of the Health and Safety
  at Work Act (HCAW).
• A minimum of 10 ACH (air changes per hour) is recommended for a dental surgery.
• If a surgery has natural ventilation only with no knowledge of what the ACH is, then AGPs
  cannot be undertaken until ventilation rates are confirmed. Confirmation of the ACH will allow
  a suitable post AGP fallow time to be calculated.
• If you are unsure what your ACH’s are – you should seek expert advice from a ventilation
  engineer.
• In addition to ensuring your practice complies with the HSAW Act, you should do all you can
  to reduce the infection hazard from aerosols. You should therefore check that your ventilation system in the surgery does not vent into other areas of the practice e.g. waiting room, staff room etc.
• Doors should be kept shut during an AGP appointment. Depending on air circulation in treatment rooms, it is expected that there will be some redistribution of small amounts of aerosol through closed doors into corridors and patient waiting/reception areas. The risk to patients and staff from these small volumes of aerosol that may escape from the treatment room is estimated to be very low.
• Clinical areas should be free of clutter.
• The number of people in the treatment room should be kept to a minimum (only team members essential for the treatment in progress).
• There is some (weak) evidence that the use of high-volume suction and rubber dam reduce the volume of aerosol and droplets in the room following an AGP. 
• Environmental cleaning after an AGP should be systematic, thorough, and documented.
• The droplet settling time is 10 minutes so cleaning can commence 10 minutes after the AGP is completed. Apolline note: This seems somewhat incongruous, since it is likely the patient will still be in the surgery 10 minutes after the AGP is completed and patients should not be in the surgery when cleaning is taking place. The level of PPE required for cleaning depends
  on the risk assessment and the calculated post AGP fallow time.
• Standard infection control procedures should be followed at all times.
• Guidance on what PPE should be worn from PHE and the devolved nations should be followed
  for all procedures.
• Special donning and doffing areas for PPE are not required. Handwashing and PPE disposal
  should be available in the immediate vicinity used for donning and doffing and strict hand
  hygiene measures should be followed.
• With at least 10 confirmed ACH per hour and additional mitigating measures in place, the
  fallow time may be reduced but it must not be reduced below 10 minutes regardless of
  ventilation because that is the time for large droplets to settle out onto surfaces.
• Recirculating air cleaning devices based on HEPA filter systems or UV-C are likely to be effective but there is little evidence of the effectiveness of all other technologies, which should
  be viewed with caution.
• The impact of recirculating air cleaning devices will depend on the air flow rate and the size
  of the room.

The second publication from NHS Scotland was a memorandum that was posted on 8th August: https://www.scottishdental.org/providing-aerosol-generating-procedures-agps-in-practice

The memorandum provides guidance (that is effective from 17th August) that the authors describe as ‘Rule of Thumb’ which they say should be followed until further definitive advice is available, thereby further underlining that much remains unknown.

The Rule of Thumb

• For a dental surgery treatment room with more than 10 air changes per hour (ACH) and for which you have evidence, a minimum of 20 minutes fallow time should be allowed before thorough cleaning takes place. 20 minutes is also the minimum time after which entrance to the surgery without full PPE is permissible.
• For a dental surgery treatment room with external ventilation (either natural or mechanical) with fewer than 10 ACH or with no data on the number of air changes per hour available, the fallow time would be 60 minutes.
• For a dental surgery treatment room with no external ventilation (either natural or mechanical), the absence of air changes means there should be no AGPs undertaken in this room.

Conclusion

• Reduction of the fallow time is dependent on the confirmed number of air changes in a room that are achievable and achieved.
• There are a number of factors that may also contribute to the ability to reduce fallow time safely.

Apolline Final Note
This document is intended only to summarise the contents of 2 new reports. We have not interpreted the guidance; we have merely summarised it.

Until officially confirmed, the national standard and the standard expected by the regulators remains at 60 minutes from cessation of the AGP. Practices that choose to alter the fallow time ahead of national guidance using mitigating factors should ensure they have clearly documented their reasons for doing so and be able to justify their actions if called upon to do so.

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Since the outbreak of the COVID-19 pandemic we have had to start thinking about the risks we face as individuals, as part of our family and home life, and the new risks faced in the dental practice.

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COVID-19 Frequently Asked Questions

We also have a dedicated page to answering the most frequently asked questions about COVID-19 where we tackled questions such as ‘What makes this virus different from other infectious diseases?’, symptoms, and things that affect dental professionals in their professional roles.