Ventilation for Clinical Areas to Minimise COVID-19 Transmission

09 July 2021 (Last updated: 6 Nov 2025 15:12)

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COVID-19 has significantly impacted the performance of a wide range of healthcare investigations due to infection control procedures. The principal mitigation when performing AGP's is changes of room air per hour (ACH).

Simple dilution of old air for new air using a standard heating, ventilation and conditioning system (HVAC) will require 28 minutes to remove 99% of the old air (10 ACH) or 41 minutes to achieve 99.9% removal. We know that fallow time falls exponentially with increasing air changes for example 50 ACH requires 6 minutes for 99% and 8 minutes for 99.9% removal efficiency compared to 2 ACH requiring 138 and 207 minutes for 99% and 99.9% respectively.

HTM03 Ventilation for Healthcare Guidance document sets out ventilation requirements for healthcare premises with minimum ventilation standards for treatment rooms being 10 ACH. However we know that in reality many centres are finding that their rooms do not achieve this standard and consequently are having to have significantly extended fallow times which is negatively impacting on capacity and ability to clear waiting lists and in some areas preventing services from re-starting.

UV-C air sterilising units have been demonstrated to effectively aid in the reduction of fallow time. The link below is to a useful tool that enables departments to calculate air removal efficiency and can also predict how the inclusion of a UV air scrubber can decrease fallow time.

Air Scrubber Clearance Calculator - http://acf-c19-support.com.s3-website.eu-west-2.amazonaws.com/

Using the online tool, below is an example of how to calculate whether or not the addition of an air scrubber would allow fallow time to decrease from 30 minutes to 10 minutes whilst maintaining current air clearance rates:
 
1.    Calculating current air clearance efficiency:
i. Existing HVAC = 5 ACH
ii. Existing ‘chosen’ Fallow Time = 30 minutes
iii. What is the Clearance? X … this is a target

2. Design for reduction in Fallow Time (30 > 10 minutes):

i. Target Fallow Period 10 minutes Y… this is a target
ii. What is the Clearance from above? X
iii. How many ACH do we need to achieve this?

ACHTotal = ACHHVAC + ACHAir_scrubber

Calculate ACHAir_scrubber (given X and Y from above)?
Is this enough to achieve our Clearance within our new 10 minute Fallow Time?

Currently there are no recommendations as to which UV Air scrubbers are most effective however Dame Prof Sue Hill has commissioned a group to look at validating systems to ensure that they deliver against their specifications. 170 systems are currently in use across Wales and pilot data in Dental surgeries across the West Midlands is demonstrating effectiveness in decreasing fallow time. Any system must be able to present independently tested, guaranteed performance results.

Please also see further information regarding this, from the NHSE/I Midlands Ventilation Webinar held on 25th May 2021. Please click here to access the webinar slides.

Best regards,

ARTP COVID-19 Group

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