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Friday, September 4, 2020

Ask your boss about the ‘fresh’ air, says trade body

Building managers should urgently review the way their ventilation systems are operating as more workers return to their offices, according to the Building Engineering Services Association (BESA).

The issue of air quality in re-opening buildings has received widespread media coverage including a feature on BBC News, which advocated workers refusing to enter “stuffy” offices as these were most likely to pose a risk of a second spike in Covid-19 infections.

BESA has been advising members of the public, contractors and end users throughout the pandemic period with a consistent message to maximise the amount of outside air being introduced to buildings to dilute the airborne viral load.

Ventilation systems should be correctly set to maximise the amount of air being brought into the occupied spaces and should be regularly maintained. The Association recommends that systems are run for longer and at higher speeds than normal – starting two hours before occupation and kept running at lower speeds overnight and at weekends to purge the building.

It is not a good idea to simply rely on opening windows, according to BESA. If there is little or no wind, the air will not naturally flow into a building from outside particularly if the temperature outside is colder than inside.

“In that case the air will flow out rather than in so even less supply air is available to the occupants,” said the Association’s head of technical Graeme Fox.

Polluted air
Another problem with opening windows is the risk of increasing the amount of polluted air entering the building, particularly in urban areas.

“There is a big difference between outside air and ‘fresh’ air,” said Nathan Wood, chair of BESA’s Health & Wellbeing in Buildings group.  “Bringing in outside air may create other risks to health if it is full of pollutants. It needs to be filtered and air purification technologies could be used in certain circumstances. The latter have been proving their worth in healthcare settings.”

It is, therefore, important to ensure mechanical ventilation and air conditioning systems are working as intended and are well maintained, he added.

Another issue to consider is when offices have been re-configured to take social distancing measures into account with desks moved and partitions erected. “This will change the way air moves around the space and, therefore, needs to be taken into account when reviewing whether the ventilation is still fit for purpose,” said Mr Wood.

Systems that recirculate the air should be switched to ‘full fresh air’ mode to minimise the risk of contaminated air re-entering the building. Recirculation dampers can usually be switched off manually or by using electronic controls. Return air from air handling units should be minimised and ‘purging’ carried out to avoid air moving from the extract side to the supply side of these units.

Filters should be regularly checked and cleaned or replaced and maintenance staff should wear full protective clothing, gloves, respirators and goggles when carrying out this work.

BESA believes that well maintained ventilation systems will play a critical role in reducing any future spread of the virus and criticised some of the evidence used by news channels to portray air conditioning as a source of contamination.

A number of reports have referred to a study that examined a Covid-19 outbreak at a restaurant in China that was blamed on an air conditioning unit. Mr Fox pointed out that the restaurant on the day in question had nearly twice as many customers squeezed in as would normally have been present – it was New Years’ Eve – and there was no outside air entering the room other than what migrated in through the lift shaft.

“The extract system used to remove stale or contaminated air was out of use,” said Mr Fox. “The only extractor was a small toilet fan at the opposite end of the room from where the diners were seated.”

He said it was “simplistic” to blame an air conditioning unit for the spread in the restaurant when it was one of four units in operation and nobody close to the other three picked up the virus.

“This was a flawed study that raised more questions than answers,” said Mr Fox. “It is being quoted repeatedly, which is simply stoking peoples’ fears. The truth is that properly maintained air conditioning and ventilation systems will reduce the risk of a second wave.

“However, if systems are not well looked after and/or there is no overall strategy for maintaining good indoor air quality, then there could be problems. That’s obvious.”

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