Disclaimer; none of the following constitutes engineering or occupational health and safety advice (from LPS). Please see the links to recognized expert guidance from OSHA and similar entities for OH&S advice.

• Occupational Health and Safety Resources

• UPDATE (July 29 2021) OSHA's current web site for Covid-19 guidance
  
• Workers' Right to Refuse Dangerous Work. Your employer cannot order you to work under unsafe conditions. Retaliation or disciplinary action for refusing to perform dangerous work is reportable to OSHA as long as your refusal is based on the four conditions listed by OSHA.
  

• GET THE VACCINE
• The vaccine is safe (my personal experience) and provides excellent protection. The doctors are right and the anti-vaxxers are wrong. This cartoon from 1802 by James Gillray (public domain due to age) shows people who received the Jenner cowpox-based smallpox vaccine (vaccine comes from vache, the French word for cow) turning into cows. Note the reference to the "anti-vaccine society" at the bottom.
  

• Respiratory Protection Information

• The Health and Safety Executive (the UK's counterpart of OSHA) found that respirators and face masks WILL provide varying degrees of protection against COVID-19. The lower levels of protection would almost certainly be deemed inadequate for a workplace where an employer has a duty of care for employee safety, but can be used by individuals for self-protection while shopping and performing other necessary activities. Here are the HSE's results.
• Screwfix mask respirator with filters: 100  (other N95 respirators, which are currently in short supply, may offer similar protection but were not cited in the reference)
  
• Mask respirator with no filter (3M 9913 is in the picture): 78
• Standard surgical mask: 6 (can be penetrated by droplets)
• Improvised from a bra or sanitary towel: 2  
  
• While a 50% reduction may not seem like much, remember that the 2019-2020 flu vaccine is only about 45% effective but it is a lot better than nothng and, if everybody got it, it could suppress contagion to a level at which seasonal flu would not be a problem as opposed to killing 20,000 to 80,000 people every year.
  
• Also (from Public Health England),"Studies in 2008 by Public Health England evaluated a range of household materials that, in the event of a pandemic, could be used by members of the general public to make individual facemasks.  These studies found that t-shirts and pillow cases made into a facemask using the design detailed below may act as a barrier against influenza."
  
• Public Health England adds, however, "'Facemasks must be worn correctly, changed frequently, removed properly, disposed of safely and used in combination with good universal hygiene behaviour in order for them to be effective."
• Reuising respirators and face masks. Rafi Letzter, 2020. "Doctors scramble for best practices on reusing medical masks during shortage"
  
• A kitchen oven at 70 degrees C (158 F) for 30 minutes works.
• Alcohol and chlorine bleach kill viruses and bacteria, but degrade the performance of N95 respirators by breaking down their electrostatic charges. (This might not, however, be an issue for improvised masks made of other materials.)
  
• Hydrogen peroxide and ultraviolet light (30 minutes) kill viruses but the effect on N95 masks' integrity is not fully known. Update; Duke Health Care found that vaporized hydrogen peroxide does not degrade N95 mask protection significantly.
• If using ultraviolet light on improvised masks, do not permit skin or eye exposure to the light. The wavelength used for sterilization (UVC) can cause skin and eye damage; it is NOT the longer wavelength (UVB) used by tanning beds (which are a bad idea anyway). See OSHA's web page for authoritative guidance.
  

• Additional Countermeasures  (does not constitute engineering or OH&S advice):

• OSHA defines as "medium risk" jobs "… those that require frequent and/or close contact with (i.e., within 6 feet of) people who may be infected with SARS-CoV-2, but who are not known or suspected COVID-19 patients." This (LPS's opinion, does not constitute engineering or OH&S advice) makes grocery shopping a medium risk activity for customers and employees. Make shopping aisles one-way to reduce the number of 6 foot proximity contacts between shoppers.
  
• This does not eliminate the risk but it reduces opportunities for the disease to spread, thus reducing its basic repoduction number R0.
• Mazzoni, Alana. 2020. "Calls for Australian supermarket giants Coles, Aldi and Woolworths to enforce one-way aisles and limit the amount of shoppers in each store."
  
• Curbside pickup and home delivery, even if more expensive, reduces face to face contacts between shoppers and store employees.
• Restaurants can consider installation of barriers between tables to reduce opportunities for contagion.
  

• Breaking (rather than Flattening) the Curve: follow the doctors' orders

• (From March 2020): Predictions that the country can reopen for business by Easter are either right or wrong, depending on how well we comply with the advice given by Surgeon General Adams and Dr. Anthony Fauci. If we do what they say to do, this menace will be suppressed by the middle of Spring, and largely wiped out by summer. If we do not do what they say (e.g. by partying on crowded beaches during Spring Break), we could have tens of millions of infections (comparable to the seasonal flu, but far more lethal), hundreds of thousands of dead, and an overload of health care systems. (July 2021): A lot of people did not follow these instructions, or get the new vaccinations, so we still have a problem. The delta variant may be a bigger problem if people remain unvaccinated.
  
• The SIR (Susceptible, Infected, Recovered) model shows how this works. (Its operation is very similar to a chemical reaction kinetics problem.)
  
• The pool of infected people increases at a rate proportional to R0*(S/N) where R0 is the virus' basic reproduction number, the average number of people an infected person will infect before he or she ceases to be contagious. S/N is the fraction of people who are susceptible to the disease, i.e. the people with no immunity divided by the total population.
  
• The pool of infected people also decreases at a rate proportional to 1 as they recover (or, in some cases, die) and can no longer transmit the disease.
• The rate of change in the pool of infected people is therefore proportional to R0(S/N)-1. We know that the top of a curve is reached when the first derivative of the underlying equation is zero. This means the course of the disease will turn around when S/N = 1/R0.
• Vaccination works by reducing S which means that, if enough people get the annual flu vaccine (they don't), we could avoid having an annual flu season along with tens of thousands of deaths and tens of billions of dollars (if not more) in economic losses.
• There is no vaccination against COVID-19 which means that, if its basic reproduction rate is 2.6 (which seems to be the best guess right now) S/N = 0.385 which means 61.5% of the population will have, or have had, COVID-19 when it peaks.
• If however social distancing, hygiene, and everything else recommended by the CDC, Surgeon General Adams, and Dr. Fauci reduce R0 to less than 1 (by simply denying the virus the ability to find new hosts--if it fails to do so, its host's immune system will kill or inactivate it), the first derivative of the infection curve will be negative which means there is no curve to flatten. As the same countermeasures work against seasonal flu, they should end the 2019-2020 flu season as well.
• ANY obstacle, regardless of how imperfect, that reduces the virus' ability to spread will reduce R0.