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       Hazards, number 152, 2020
VENTING | Coronavirus risks are mostly up in the air
Hands, face, space. We all know the mantra. But you can’t stop breathing and if the workplace air is going nowhere and is chock-full of coronavirus, you’ll still be at risk. Hilda Palmer of the Hazards Campaign explains the critical importance of ventilation and why it is necessary to clear the air.


Coronavirus is in the air. It spreads like smoke in tiny aerosol particles exhaled by infected individuals with every breath. The prevention three amigos of ‘hands, face, space’ deals with contact and droplet risks - but does not address transmission of virus-laden airborne aerosols.

A microscopic, invisible virus-carrying cloud – a ‘far-field aerosol’ – can get you at a distance. It is likely to be the most important mode of transmission.

PROBLEM AIRED  There is ‘overwhelming evidence’ that inhalation of the coronavirus represents a major transmission route for Covid-19, scientists have said. The warning from experts from six US universities reinforces the findings of other studies, and demonstrates the critical importance of suitable ventilation to protect workers. more

This isn’t just theory - infectious disease experts, aerosols scientists and epidemiologists have established the risk of aerosol transmission in Covid-19 case studies, sentinel cases, super spreader events, cluster outbreaks and laboratory experiments. 

It was months before the UK government, Public Health England and the UK government’s SAGE scientific advisory panel conceded the airborne transmission risk (Hazards 151).

And specific guidance from the workplace safety regulator the Health and Safety Executive (HSE) was late and remains weak and unenforced. The consequence has been hundreds of workplace clusters each week, some seeing hundreds of workers test positive and some die [see: Covid-19 deaths at 3.4 times the rate for all other work fatalities].

Every breath you take

SARS Cov-2, the coronavirus responsible for Covid-19, infects a person when it is inhaled (droplet and airborne transmission) or gets into the mouth and nose via touch (fomite transmission). 

BUTCHERED Several major food processors have seen outbreaks at several of their plants. In December, the multinational Bakkavor agreed to pay self-isolating workers at a plant their full pay after a second worker died of Covid-19. In November, meat processing plants in Aberdeenshire and Cornwall operated by Kepak were hit by large Covid-19 outbreaks, with a total of around 200 workers testing positive.  more

Droplets in spit or exhaled can evaporate to become smaller aerosols, and spread further. Aerosols can fill a room and linger in the air for seconds to hours, often after the infected person has left. They fall out of the air, are deposited on surfaces and can be recirculated by air currents.

Virus concentrations can build up in indoor areas that are poorly ventilated, where workers breathe shared air for hours at a time. Aerosols persist longer in colder, drier air, an added occupational risk in jobs like food processing [see: Bad jobs cause virus spread in meat plants].

Face masks can help, but good ventilation is critical to reducing the viral load in the air. Lower loads reduce the risk of infection and the severity of infection. Effective ventilation removes stale air and brings in cooler, drier air containing more oxygen, less carbon dioxide (CO) and water vapour and fewer microbes. 

The concentration of carbon dioxide in indoor air provides a useful indication of how well the ventilation is functioning. Carbon dioxide increases from 0.04 per cent to 4 per cent in exhaled breath. Outside air contains 300-400 parts per million (ppm) carbon dioxide near ground level.

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.

A November 2020 working paper for the global foodworkers’ union IUF found poor ventilation was one of the key factors responsible for major and frequently deadly outbreaks in meat processing plants around the world, with this compounded by overcrowding, a lack of paid sick leave and other factors including low temperatures, a lack of PPE and incentive pay schemes.

AND BREATHE Carbon dioxide (CO) monitors can give a rough indication of how well your workplace ventilation – whether it’s via an open door or a full-on mechanical system – is working.

It noted “well designed and maintained” ventilation systems “can be an important factor in preventing Covid from spreading indoors by increasing clean air flow and maintaining indoor conditions (temperature and humidity) that discourage virus survival.”

Poor ventilation, recirculation of shared air and poor maintenance of air conditioning systems can all increase transmission in workplaces.

There is no one silver bullet that is 100 per cent effective to prevent infection from coronavirus in near- and far-field aerosols. But a combination of good ventilation, 2 metre minimum distancing and PPE all contribute to overall protection.

This is doubly important as it now seems clear most people who are infectious will be exhibiting no symptoms. A study published in the journal Clinical Epidemiology on 8 October 2020 reported over threequarters (76.5 per cent) of people in England testing positive for the coronavirus responsible for Covid-19 – SARS-CoV-2 – had no symptoms on the day of the test, with another 10 per cent having none of the core symptoms.

In the absence of routine, effective and comprehensive workplace testing, this means infected individuals will inevitably end up at work.

Ventilation rules

An infectious person may exhale 100,000 to 10 million virus particles an hour, so effective ventilation is essential to infection prevention. UK guidance was slow to recognise this.

It was as recently as 26 November 2020 when the UK business department BEIS issued updated workplace guidance, with an ‘objective’ recommending “ventilation to mitigate the transmission risk of Covid-19.”

The BEIS guide notes: “Good ventilation can be different for areas depending on how many people are in there, how the space is being used, and the particular layout of the area. Therefore you will need to consider the particular ventilation requirements in the area you are considering.” 

‘Ventilation and air conditioning during the coronavirus (Covid-19) pandemic’, an HSE guide published in December 2020, notes: “Good ventilation, together with social distancing, keeping your workplace clean and frequent handwashing, can help reduce the risk of spreading coronavirus.”

The Workplace (Health, Safety and Welfare) Regulations lays down the legal ventilation requirements at work. The regulations note: “Effective and suitable provision shall be made to ensure that every enclosed workplace is ventilated by a sufficient quantity of fresh or purified air. The fresh-air supply rate should not normally fall below 5 to 8 litres per second, per occupant. When establishing a fresh-air supply rate, consider the following factors: the floor area per person; the processes and equipment involved; whether the work is strenuous.”

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 and repeats the importance of avoiding recirculating air. That’s your benchmark.

Assessing the risks

Ventilation systems can be as simple as opening windows and doors to complex centralised Heating Air Conditioning Ventilation systems (HACV). Find out the type of ventilation system in your workplace, how well it is performing in removing stale shared air and bringing in fresh air.

The employer should provide safety reps with information about the workplace ventilation system – is it providing the recommended air flow, is it maintained properly, are the correct filters in use and replaced and maintained frequently? Ask for monitoring and maintenance data, including CO levels.

A paper published in the journal Toxicology and Industrial Health on 26 November 2020 noted: “Given the current debate regarding transmission of small airborne aerosols, ventilation systems should be used and maintained correctly in order to maximize the utility of the system, reduce the risk of indoor airborne infection, and reduce the possibility that the systems themselves may transmit and spread the disease (as has been reported by some authors).

“Checking the ventilation system to make sure that the system is properly configured, maintained, and cleaned, that proper filters are installed, that everything is working properly, that there is an increase in the amount of outdoor air, and that there is constant air movement can reduce the risk of Covid-19 transmission. However, just having a ventilation system installed in a building is not enough.”

Workplace risk assessment must consider all the factors affecting the risk of inhaling near- and far-field aerosols. Key factors to consider are:

Location  Outdoors less risk, indoor workplaces higher risk, increasing with factors below.

Occupancy  Halving occupancy is equivalent to doubling the ventilation rate. Remember, though, that aerosols can linger for minutes or hours, so previous occupancy levels may create lingering risk.

Infection levels  Research suggests that around half of coronavirus transmission could be from people with no symptoms (asymptomatic).

Proximity  2 metres physical distancing is a rough minimum distance to avoid inhaling high concentrations of near-field aerosols or being sprayed with droplets.

Duration  The longer spent in a space with poor ventilation, the higher the risk.

Activity  Aerosols are exhaled when breathing and talking. Loud talking, singing, aerobic activity result in more potentially virus-loaded aerosols being exhaled.

Environment  Cooler, darker and drier conditions assist aerosol spread and persistence; higher temperature and humidity shorten the survival time of the virus.

Air flow  The lower the air flow the higher the risk. Doubling the ventilation rate per person can halve the infection risk.

Masks  Face masks use can reduce the amount of virus in the air and is particularly effective if they are used ‘properly’ and by all occupants of the room.


Safety reps’ checklist

Do risk assessments consider ventilation requirements?
Have safety reps been consulted on the Covid risk assessments?
Is the ventilation system effective and maintained?
Is the air flow at least 10 litres per second per person with a minimum of six air changes per hour?
Is the ventilation system set for 100 per cent outdoor air to prevent recirculation, turned on 2 hours before occupation, and automatic CO sensor switching off or set to 400ppm?
If there is no ventilation system, does natural ventilation create an unhealthy or uncomfortable work environment (temperature, noise, pollution) or pose a risk of spreading infection?
Are areas with inadequate ventilation taken out of use or are alternative methods to reduce risk used (eg reducing occupancy, use of upper room UV disinfection, portable HEPA air filtration units)?
Are rooms subject to periods of no occupancy to allow contaminants to dissipate?
Are rooms cleaned regularly to reduce recirculation of any virus deposited on surfaces, adsorbed on dust?
Is the relative humidity too low and the air too dry?



Hazards Campaign
• Linsey Marr, Applied Interdisciplinary Research in Air, Virginia Tech.
• Shelly L Miller, University of Colorado Boulder.



Airborne virus a ‘major’ transmission risk

There is ‘overwhelming evidence’ that inhalation of the coronavirus represents a major transmission route for Covid-19, scientists have said. The warning from experts from six US universities contradicts a position promoted by the World Health Organisation (WHO), which has played down airborne risks and said transmission by larger droplets is the predominant mode of transmission.

However the letter published in Science magazine on 30 September 2020, notes “aerosols containing infectious virus can also travel more than 2m and accumulate in poorly ventilated indoor air, leading to superspreading events.”

The letter adds: “Individuals with Covid-19, many of whom have no symptoms, release thousands of virus-laden aerosols and far fewer droplets when breathing and talking. Thus, one is far more likely to inhale aerosols than be sprayed by a droplet, and so the balance of attention must be shifted to protecting against airborne transmission.

“In addition to existing mandates of mask-wearing, social distancing, and hygiene efforts, we urge public health officials to add clear guidance about the importance of moving activities outdoors, improving indoor air using ventilation and filtration, and improving protection for high risk workers.”

In September 2020, Public Health England departed from the WHO line, with revised guidance noting: “Airborne transmission may also occur in poorly ventilated indoor spaces, particularly if individuals are in the same room together for an extended period of time”. The US Centers for Disease Control followed suit in October.

Airborne transmission helps explain the high number of outbreaks in non-health and social care workplaces, and high death rates in a wide range of jobs.

Kimberly A. Prather, Linsey C Marr, Robert T Schooley and others. Airborne transmission of SARS-CoV-2, Science, 5 October 2020. DOI: 10.1126/science.abf0521
COVID-19: epidemiology, virology and clinical features, PHE guidance, updated 30 September 2020.

Back to main story

Bakkavor agrees sick pay after deaths

Workers at a Bakkavor factory claimed a massive victory after the major fresh food supplier agreed full pay for staff off work because of a Covid outbreak.  The GMB said the company also agreed a roll out of mass testing at the Tilmanstone salads site in Kent.

The food supply multinational, which supplies major retailers including Marks and Spencer, has also carried out a deep clean of the factory. The move came in December 2020 after confirmation of two Covid-related deaths of workers from the Tilmanstone factory. GMB said cases in an outbreak at the factory had ‘rocketed’ from around 35 in the third week of November to 99 as of 3 December.

Frank Macklin, GMB regional organiser, said: “These changes will help save lives and go a long way to making Tilmanstone Salads factory as safe a place as possible to work in during this current crisis. Full pay for staff who test positive, now means that our members can sleep easy at night, safe in the knowledge that if they do test positive their wage is secure and they won’t have to worry about putting bread on the table.”

He added: “After a tragic few weeks we’ll be working with Bakkavor to roll out these measures which we hope will lead to a significant drop in Covid cases.”

Bakkavor changed tack after GMB lodged a formal collective grievance on behalf of its members at the plant, with the GMB officer stating “we believe the health and safety of our members has been seriously compromised at the factory.”

The company has faced criticism for its safety record previously and has been prosecuted twice in the last three years for criminal safety offences following two workplace deaths in separate incidents.

On 30 November, the TUC warned food processing factories could become “super spreaders” of Covid-19 in the run up to Christmas.

The union body says people working in food plants already face a higher chance of contracting Covid-19 due to the lack of airflow, lack of social distancing and low temperatures. With the number of temporary workers in food manufacturing set to increase by more than 40 per cent this Christmas, the union body says the risk of workplace infections will grow.

Since March, several UK food factories have been forced to close during the pandemic after reporting hundreds of cases of coronavirus, among them suppliers to major supermarkets.

The TUC warns that current workplace safety guidance for food production is “out-of-date”. Studies have shown the significance of airborne transmission, with Covid-19 aerosols remaining suspended in the air for hours.

But the existing government guidance is still largely based on stopping spread of droplets which fall to the ground in seconds. The TUC wants stricter controls on ventilation, face coverings, workplace temperatures and physical distancing.

TUC general secretary Frances O'Grady said: “There is a real danger that food factories could become 'super spreaders' of Covid-19 as they produce turkeys and other seasonal fare for Christmas. Out-of-date guidelines on food production, combined with the seasonal increase in staff, will put factory workers at an even higher risk of infection.”

The TUC leader added: “Ministers urgently need to update the guidance for food production. They must require employers to publish their risk assessments. And they must resource the HSE properly, so it can get into food factories and crack down on unsafe working. That’s how to make sure everyone is safe at work this Christmas.”

The TUC said too little official safety enforcement action is taking place, with the Health and Safety Executive (HSE) issuing just 31 enforcement notices for Covid-19 safety breaches between April and the end of November 2020.

Many major food processors have seen outbreaks at several plants. In November, plants in Aberdeenshire and Cornwall operated by Kepak were hit by large Covid-19 outbreaks, with a total of around 200 workers testing positive.

Back to main story

Bad jobs cause virus spread in meat plants

Bad work practices have a clear link to the high rates of Covid-19 outbreaks in meat processing plants, public health experts have warned. The findings by a team of researchers led by Dr David Nabarro, the co-director of the Institute for Global Health Innovation at Imperial College London, come in a working paper for the global foodworkers’ union IUF.

The paper recommends ‘essential and practical steps employers and regulatory agencies should take’ to mitigate against the spread of the disease in meat and other cold food processing environments. The report notes employment conditions which incentivise reporting systems and provide financial support to workers when sick or isolating are critical in the successful fight against the disease.

It notes temperature, humidity and poor ventilation all play a role in the spread of the disease. Crowded workplaces, the speed of production, and aerosols combining with dust, feathers and animal waste, are all factors which encourage transmission of the coronavirus, it adds.

IUF assistant general secretary James Ritchie commented: “A healthy and safe workplace established through the elimination and control of hazards, thorough testing and contact tracing systems enacted by appropriately funded public health authorities, and adequate paid sick leave for workers who are sick or must isolate, are the essential components of a strategy to keep essential food workers safe and to fight the spread of the coronavirus. There is no excuse to delay implementation.”

A study by a team from St Johns Institute of Dermatology, Guy’s Hospital reached the same conclusions, noting low temperatures, low air exchange rates, air recirculation and other poor elements of job design contributed to the high number of outbreaks.

In an editorial in the journal Occupational Medicine, they noted other contributory factors included “insufficient distancing between workers, poor compliance with facemask use, presenteeism because of insecure poorly paid employment, voice projection against a background of loud machinery, hyperpnoea [faster breathing] because of heavy manual labour, limited or non-existent hygiene measures and overcrowded domestic accommodation for migrant workers.”

COVID in cold environments: risks in meat processing plants, full working paper for IUF in in English, French, German, Portuguese and Spanish, 11 November 2020.
Louise Cunningham, Paul J Nicholson, Jane O’Connor, John P McFadden. Cold working environments as an occupational risk factor for COVID-19, Occupational Medicine, kqaa195, Published: 28 November 2020. https://doi.org/10.1093/occmed/kqaa195


Air conditioning win for bus drivers

The announcement that London buses have been fitted with an improved, safer air conditioning system has been greeted by Unite as a ‘major victory’. All London buses have had changes made to their air conditioning systems so that the air entering the driver’s sealed cab comes directly from the outside and does not pass through the passenger area of the bus.

The union says the change will greatly reduce the risk of bus drivers being exposed to the coronavirus while driving. Unite first raised concerns about the air conditioning system with Transport for London (TfL) and bus operators in February, before the initial national lockdown.

Unite lead officer for London buses John Murphy said: “This is a major victory in Unite’s continuing campaign to improve the safety of London buses during the pandemic. Unite highlighted its concerns about the air conditioning system when the first cases of Covid-19 began to emerge and it was instrumental in ensuring the air conditioning was turned off and a replacement system introduced.”

He added: “While this was a positive development, Unite will not rest on its laurels and is continuously ensuring that drivers’ safety is maintained and improved throughout the second wave of the pandemic. London bus drivers have continued to work throughout the pandemic and have kept London moving, with too many paying a tragic price, it is incumbent on everyone involved with buses that no stone is left unturned in ensuring their safety.”


Top of the page






Hands, face, space. We all know the mantra. But you can’t stop breathing and if the workplace air is going nowhere and is chock-full of coronavirus, you’ll still be at risk. Hilda Palmer of the Hazards Campaign explains the critical importance of ventilation and why it is necessary to clear the air.

Every breath you take
Ventilation rules
Assessing the risks
Safety reps’ checklist

Other stories
Airborne virus a ‘major’ transmission risk
Bakkavor agrees sick pay after deaths
Bad jobs cause virus spread in meat plants
Air conditioning win for bus drivers

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Work and health

See the dedicated Hazards coronavirus resources pages.