Key questions to ask your employer on ventilation in your workplace/classroom.

Dear Barnet UNISON members

In light of the Governments’ decision to reopen schools our branch want to make sure that we can provide as much support for all of our members who are going into work.

Good Ventilation is key to making a workplace/classroom safe.

I hope this briefing will provide useful for our members to be able to use for your workplace Risk Assessments which need to be updated. We have provided some questions you may want to submit to your employer.

Please let us know if you need help.


  • Covid Spread widely in school last term and contributed to the huge rise in overall community infection rate leading to increased restrictions and lockdown.
  • Government accepted this and closed schools to face to face teaching in January, apart from key workers’ and vulnerable children.
  • Early Years provision continued and so did the rate of infection in those age groups with many outbreaks in Nurseries and schools affecting children, staff and families.
  • New Covid variants which became common  in the Autumn are now known to be be more transmissible- maybe 30-70% more transmissible- and also more lethal.
  • It is imperative to reduce transmission of this airborne virus and measures taken last year in school need to be improved far more due to the new variants.

The Government SAGE EMG group reviewed the need for mitigations to reduce transmission of the new Covid variants and recommended that previous ventilation measures should be increased by 1.5 to 1.7 times.

Mitigations to reduce transmission of the new variant SARS-CoV-2 virus, 22 December 2020 (;:

Relevant para: 12. Transmission via the air is primarily mitigated by effective ventilation vi. This is most important in workplace and public settings where people interact, and is also important in the home, especially if there are visitors from outside the household, or someone within it has COVID-19. Where provision of adequate ventilation is difficult, the use of air cleaning devices may be a suitable alternative vii . Higher viral load associated with people who have the new variant could have significant implications for transmission via the air, as previous modelling suggests that viral load is a major determinant of airborne transmission risks. As a precautionary measure it is recommended that ventilation rates stated in previous EMG papersvi are adjusted accordingly to account for the increased risk (potentially 1.5-1.7 times higher). Application of ventilation controls is currently very variable between different settings, and it is essential to ensure that all public and workplace spaces include ventilation as part of their COVID secure risk assessment, and adopt appropriate measures to ensure it is effective (high confidence).

HSE references technical guidance from the building services professional body, CIBSE.

An October 2020 CIBSE update recommends a minimum of 10 litres per second per person of outside air in offices/classrooms and repeats the importance of avoiding recirculating air.

CIBSE Version 4 CIBSE – Emerging from Lockdown;

See Hazards Magazine Venting

  • Measuring CO2 levels is a rough proxy measurement of ventilation
  • Indoor air at 600 to 800 ppm carbon dioxide indicates a relatively well-ventilated room.
  • Over 1,500 ppm means very poor ventilation and action is needed.
  • A minimum of six air changes per hour is recommended.

Key questions on ventilation in your workplace/classroom to ask your employer.

1. What is the airflow level in the workplace/classroom when unoccupied and occupied?

2. What level of outdoor/fresh air per person per second does the ventilation system provide in each workspace/classroom? (Please note CIBSE recommends airflow of 10 litres per person per second of fresh/outdoor and the WHO recommends 6 Room Air changes per hour)

3. Is data provided from a proven competent expert?

4. What are you using to monitor safe airflow levels in each workplace/classroom? For example CO2 monitors can provide a rough proxy measurement of ventilation: 600 to 800 ppm carbon dioxide indicates a relatively well-ventilated room.

5. How regularly are you monitoring safe airflow levels in each workplace/classroom during the day before occupancy and during occupancy?

6. What is the plan of action if airflow levels are unsafe? 


You can contact the Barnet UNISON branch on 0208 359 2088 or email