Lydia Bourouiba, an MIT professor and director of the Fluid Dynamics of Disease Transmission Laboratory, writes that our current six-foot safety zone is based on decades-old work in a laboratory and that might be putting health-care providers at risk.
In "Turbulent Gas Clouds and Respiratory Pathogen Emissions," Bourouiba shows rather graphically, via a couple of videos, how a sneeze can propel nasal droplets as far as 27 feet. Also:
Recent work has demonstrated that exhalations, sneezes, and coughs not only consist of mucosalivary droplets following short-range semiballistic emission trajectories but, importantly, are primarily made of a multiphase turbulent gas (a puff) cloud that entrains ambient air and traps and carries within it clusters of droplets with a continuum of droplet sizes. ... The locally moist and warm atmosphere within the turbulent gas cloud allows the contained droplets to evade evaporation for much longer than occurs with isolated droplets. Under these conditions, the lifetime of a droplet could be considerably extended by a factor of up to 1000, from a fraction of a second to minutes.
She notes that the current dichotomy between "aerosolized" infections, such as measles, and ones that you pick up by touching infected surfaces and then your face, is based on experiments done in the 1930s, and that the rapid spread of Covid-19 suggests it's time for a new paradigm:
Even when maximum containment policies were enforced, the rapid international spread of COVID-19 suggests that using arbitrary droplet size cutoffs may not accurately reflect what actually occurs with respiratory emissions, possibly contributing to the ineffectiveness of some procedures used to limit the spread of respiratory disease.
She concludes that the findings are particularly important for healthcare workers, because they should, ideally, be using personal protective equipment at distances of more than six feet from a patient - and which can "repeatedly withstand the kind of high-momentum multiphase turbulent gas cloud that may be ejected during a sneeze or a cough and the exposure from them." Current N95 masks, she writes, are not tested for this.