https://www.hse.gov.uk/coronavirus/equipment-and-machinery/air-conditioning-and-ventilation/index.htm

Sorry Herb you are going to have to provide the information where the HSE have said "No":

The law says employers must make sure there’s an adequate supply of fresh air (ventilation) in enclosed areas of the workplace. This has not changed during the pandemic.

You should be maximising the fresh air in a space and this can be done by:

natural ventilation which relies on passive air flow through windows, doors and air vents that can be fully or partially opened mechanical ventilation using fans and ducts to bring in fresh air from outside, or  a combination of natural and mechanical ventilation, for example where mechanical ventilation relies on natural ventilation to maximise fresh air

You shouldn't have staff working in a poorly ventilated place in the first instance so my first thoughts would be to either increase ventilation or move the staff to a well ventilated spot rather than whether fans can be used in a poorly ventilated area.

Fans do not provide ventilation; they simply move the air about and have a cooling effect on the skin. Ventilation refers to the supply of fresh clean air either naturally from a window or similar,  or by artificial means. If it is ventilated by artificial means the air supplied must be “clean” , that is means it can’t be the same old being recirculated through the room. It will be filtered and topped up with air from outside. Such a system must be maintained etc.

Adding to this the concerns with airborne microorganisms especially  Covid-19, means a fan is even less appropriate. See https://www.hse.gov.uk/coronavirus/equipment-and-machinery/air-conditioning-and-ventilation/index.htm

If the windows are all open it probably isn't poorly ventilated.

I wouldnt say offices are poorly ventilated, thats a personal opinion on whether the aim is humid or not.  personally as someone who has asthma, I can detect the humidity of a room immediately and it can cause a slightly more difficulties in breathing, however not to the point that it becomes dangerous to me.

If you were working in  a confinded space, such as a backup generator which are normally enclosed in brick and a meter all around it, then yes, this is poor airflow, therefore breathing aparatus is used.

Originally Posted by: biker1

Given the current concerns about transmission and spread of COVID, I would say that desk fans in an office are a definite no-no.

I'm not a great lover of fans but understand they have their uses.

I'm sure I read a headline about the perspex screens that everyone seems to have in the office being a negative now as they prevent air circulating around the office. The wondows and any air handling system will of been designed/placed to suit the office, we then go and place all these perspex screen in and completely ruin the flow of air around the office.

Incidentaly, has anyone removed the screens yet?

Same as SteveM, never needed to put them up as we had ample space and opportunity to arrange the office so that everyone is 2m+ apart

The effectiveness of ventilation as a Covid measure is dependent on it bringing in fresh air.  Just circulating what is already there is useless at best.  But proper ventilation is now accepted as a useful control measure to the extent that it is listed as a "priority measure" for businesses to take - see for example Offices and contact centres - Working safely during coronavirus (COVID-19) - Guidance - GOV.UK (www.gov.uk)