Why is the 2 metre rule for social distancing rules safe?

As the UK gradually returns to work the question often asked is why does keeping 2 metres away from people stop the spread of Coronavirus. In particular how does this rule apply to a risk control measure to help prevent Covid-19 in the workplace.

The hospitality industry in particular has asked the prime minister to look into whether customers and staff must stay two metres apart. So what factors were considered when deciding upon the 2 metre rule.

Research from the 1930s found that droplets of liquid released by coughs or sneezes actually evaporate quickly in the air or fall to the ground. In fact most of these droplets would land within 1-2m of the person coughing or sneezing.

It is now accepted that Coronavirus and thus Covid-19 can be spread in droplets of liquid from an infected persons cough or sneeze.

So, now we know, coughing or breathing out from an infected person has little chance of droplets reaching another person and thus infecting them. However, a sneeze - well that is an entirely different matter.

Simply put, the nearer you are to an infected person, the greater your risk of catching the virus. The World Health Organization takes a different view from the UK government and recommends keeping a distance of minimum 1m.

Other countries have adopted different social distance rules, often reduced where the wearing of face masks is compulsory.

• 1m distancing rule - China, Denmark, France, Hong Kong, Lithuania, Singapore
• 1.4m - South Korea
• 1.5m - Australia, Belgium, Germany, Greece, Italy, Netherlands, Portugal
• 1.8m - US
• 2m - Canada, Spain, UK

UK latest studies and reports on social distances

The Lancet medical journal has just published a report into how coronavirus spreads. Some of the conculsions were:

• Keeping at least 1m from other people could be the best way to limit the chances of infection.
• The risk of being infected is estimated to be 13% within 1m, but drops to only 3% at more than 1m.
• For every extra metre of distance up to 3m, the risk is further reduced by half.

Distance is not the only factor

The amount of time spent near an infectious person also plays a part. The longer you spend near an infected person, the bigger the risk.

Current research says spending six seconds at a distance of 1 metre from an infectious person is the same as spending one minute at a distance of 2 metres.

However this risk changes dramatically if the infectious person coughs. Then being 2m away from a single cough is the same risk as talking to you for 30 minutes from the same distance.

Ventilation also matters

We have probably all heard via various sources that you are less likely to be infected by coronavirus outside in the fresh air. A crowded stuffy room is always going to increase the chances of infection as infectious droplets are not dispersed.

However the flow of air is also important - for instance is a draught or fan behind an infectious person pushing any droplets they breathe out towards you?

A good supply of fresh air can be vital. For instance air conditioning units in a restaurant in China were implicated in spreading the coronavirus to 9 people, by recirculating contaminated air rather than just opening a window.

Japanese researchers have estimated the chances of infection are nearly 19 times higher indoors than outside.

What about where it is impossible to stay more than 1 or 2 metres apart?

Plastic screens are one suggestion, changing shift patterns to minimise the workers in at any one time. Arranging seating so people are not face to face is helpful in lowering the risk. Wearing a face covering is almost certain to be more and more widely adopted.

There is lots more useful information and how to carry out a workplace risk assessment in our online course COVID-19 | Workplace Preparedness