(COVID-19) UPDATE AND RESOURCES (March 28 2020)
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
- Occupational Health and Safety
- Respiratory Protection
- 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
- 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
- Standard surgical mask: 6 (can be penetrated by
- 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
- 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.
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.
(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
- This does not eliminate the risk but it reduces
opportunities for the disease to spread, thus reducing its basic
repoduction number R0.
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
- Restaurants can consider installation
of barriers between tables to reduce opportunities for contagion.
- Breaking (rather than
Flattening) the Curve: follow the doctors' orders
Takeaway: FOLLOW THE
DOCTORS' ORDERS AND DON'T HESITATE TO TELL (POLITELY) ANYBODY WHO
DOESN'T HOW THEY ARE ENDANGERING THEIR OWN SAFETY AND THAT OF OTHERS.
- 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
- 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.
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
- ANY obstacle, regardless of how imperfect, that
reduces the virus' ability to spread will reduce R0.