ACH and Fallow Times - Where do we Stand?

Recently updated guidance in some parts of the UK has led to debates around the issue of air changes per hour (ACH) and how this impacts on the fallow time following an aerosol generating procedure (AGP).

This document aims to:

  • Define the term ACH.
  • Summarise the current guidelines in relation to fallow times post-AGP across the UK and Ireland.
  • Review various solutions aimed at increasing ACH.

ACH

Air changes per hour (ACH) is a measure of the air volume added to or removed from a space (denoted as “CFM”) in an hour divided by the total volume of the space.

ACH = Cubic Feet per Minute (CFM) x 60 min / Length x Width x Height of room                         

For example: 4 (CFM) x 60 (min) /40m3 = 6 ACH

The faster the air circulation i.e. the higher the CFM, the higher ACH will be, meaning that airborne pathogens (including virus particles) can be removed quicker. Subsequently this will positively impact on the fallow time required post-AGP during the current pandemic.

N.B. Fallow time is calculated from the point that the AGP ceases.

Current Guidelines (for neutral pressure rooms)

England

The latest SOP update from the Chief Dental Officer dated 28 August 2020, recommends the following post-AGP fallow periods:

  • A room with 6 ACH: 60 mins.
  • A room with 10-12 ACH: 20 mins.
  • Windows should be left open where possible and applicable.

Wales

The latest SOP update from the Chief Dental Officer dated 26 August 2020, recommends the following post-AGP fallow periods:

  • A room with ≥10 ACH for Short AGP treatments (<10 mins) +using high volume suction: 16 mins
  • A room with ≥10 ACH for Long AGP treatments (40 mins) +using high volume suction: 18 mins
  • Where other mitigating factors are also used e.g. rubber dam, fallow times cannot be below 10 mins.
  • No AGPs in windowless rooms with <6 ACH.

Scotland

The SOP dated 30 July 2020, recommends the following post-AGP fallow periods:

  • A room with <10 ACH: 60 mins
  • A room with ≥10 ACH: 20 mins
  • No AGPs in rooms without external ventilation (natural or mechanical).

Northern Ireland (NI)

The HSC Board’s Operational Guidance updated on 22 June 2020, recommends the following post-AGP fallow period: 60 mins. A further update is expected imminently to bring NI in line with other UK counterparts.

Republic of Ireland

There is NO FALLOW PERIOD post-AGP for “non-Covid19” patients, and a fallow period of 60 mins for those who are confirmed as Covid19 positive.   

How can ACH be increased?

Proven solutions with a good evidence base:

  1. HEPA filters
  2. Electrostatic Precipitator (ESP) filters

Unproven solutions with a weak evidence base and further issues to note as detailed below:

  1. Air extraction fans - very slow to displace air.
  2. Charcoal filters – minimally effective in removing bacteria and viruses.
  3. UVC lamps – require precise positioning to ensure UV rays assert their effect directly and kill microorganisms. Additionally, direct exposure to UVC radiation can damage the skin and eyes.
  4. Fogging – long term health (respiratory) effects on staff are unknown.

Is there equipment available to meet these guidelines?

DD have carefully selected partners to investigate the saturated space of air filtration to ensure that dentists can procure a range of evidence-based solutions, supported by robust scientific testing carried out by expert engineers with air cleaning and quality management experience. The following selection of products are available that provide for differing situations. Please note that building work for air extraction is not necessary when using the following types of equipment.

Aeramax Professional 4 (wall mounted unit)

Manufactured by Fellowes, who have carried out testing to show that in a 40m3 room, an ACH of 12 can be achieved - resulting in an 18.1 min fallow time. This equipment is wall mounted in the appropriate area.

AirHavn Pro (floor standing)

Manufactured by AirLabs, who have carried out testing to show that in a 40m3 room, an ACH of 20 can be achieved – resulting in a 12 min fallow time. This equipment has wheels on the undercarriage so is more mobile.

DD’s equipment team are working closely with its partners at Fellowes and AirLabs, who have experts on hand to deal with queries and assist with calculating what ACH can be achieved using these unique solutions based on a surgery size. DD’s objective is to help dentists calculate a safe post-AGP fallow time, enabling an increase in patient flow whilst maintaining safe premises.

For further information, please watch DD’s recent webinars delivered by the experts in air cleaning technology.

AirHavn Pro Air Purifier

AeraMax Professional IV Air Purifier - Wall Mounted

DD can arrange for supply of this equipment. Call the team on 0800 585 586 or email equipmentsales@ddgroup.com to obtain a FREE quote and discuss FINANCE PACKAGES should that be necessary.