Quote Originally Posted by HK_Katherine:
Evidence? Sounds like numbers you are pulling out of the air. Most countries are using 2m separation outside. For restaurants in HK, it's 1.5m separation INSIDE (and inside is clearly much higher level of risk than outside).
No need to prove any data with you, after your few posts on how you do data analysis.

Jokes aside, 2 meters outside it is probably a safe number due to several reasons, from the droplet travel distance and the evaporation factor (basically from the size of a droplet, it is not particularly complicated to calculate how far they can travel and how they can evaporate, partially or totally).
Consider that normal breathing runs at approximately 1m/s, coughing 10m/s, sneezing can go up to 50.

Having considered the above, a safe distance outside would probably be 2.5 meters (I can agree on 2 in certain scenarios) and I would consider 6 for indoor, however we cannot implement these solutions effectively, specially in crowded places like Hong Kong.
Let's look at the average 茶餐廳 / Cha Chaan Teng, if we had to implement a safe distance of 6 meters, we would most likely have 2xtwo seaters table: not doable.
So we are considering that the majority of droplets of.a certain size are usually evaporating before the 2 meters distance, and we have made a trade off with that, but that is absolutely not a safety distance, but let's say an OK trade off (that I would have not authorised for the whole end of February and March, if I were in the government hands).