Toast Test--Simulated Testing of Indoor Spaces for COVID Spread
Introduction: Toast Test--Simulated Testing of Indoor Spaces for COVID Spread
COVID is spread by micro droplets that hang in the air for hours. Statistically it does not appear to be spread by surfaces so a lot of the rules that we use for keeping safe are unlikely to help--breath barriers, obsessive washing of everything. Incredible real life examples of how it is spread are now obvious in retrospect: an airplane packed with 400 spreaders of virus, not respecting distancing, half the time with their masks off, no breath barriers between seats--no one gets COVID. Why? Airplanes change out their air once every three minutes and 75% of it is from outside. You should be so lucky with your teammates for a beer after a game at the corner bar....Well now you can be with the Toast Test. It is a simple reproducible way of evaluating the factors that make for a safe COVID environment.
Much scientific study has gone into modeling of indoor environments for the spread of virus particles. The algorithms used are very complex and rely on an untold number of assumptions. In-Vivo virus distribution experiments have also been done with a variety of closed environments but they rely on extensive testing methods and are dangerous if using live virus. What is needed is a test that mimics the movement of viral aerosols, is easy to track, reproducible, and responds to the same forces that we know decrease virus transmission risk: diluting air movement, HEPA filtration and ventilation.
The Toast Test has nothing to do with the great news that Toast of London is now signed up for a new season. Rather it is an easily built, battery operated, unit that uses the virus simulating effects of a toaster smoke plume to follow the potential for COVID safety in inside environments.
Step 1: The Theory
Much recent work supports the concept that these coronaviruses behave like other respiratory viruses tending to spread in particles that are below 2.5 microns in size. Hacked particles from coughing that behave like missiles and hit the ground or evaporate quickly are eliminated by their large physical size do not predominate. A super spreader with a normal speaking voice can manufacture a floating cloud of 6000 particles in about 10 minutes. Symptomatic cough spreaders produce the chunks that do not go deeply into your lungs like the small floaters that dive toward your alveoli. It's rare these days to see a symptomatic cougher out in public.
Smoke particles from Burning Toast are about 2.5 microns in size. They are used frequently for the testing of the efficiency of HEPA filtration systems. 225
(Wirecutter does their annual test of HEPPA filtration by lighting 4 matches for their smoke to fill a test room.) They behave like any particle in this size range--hanging for hours and blown about by fans, filters and out open window. The great thing about them and the basis of the toast test is that very cheap and accurate sensors exist for following their level and enable you to accurately count them without resorting to massive computer simulations or risking peoples lives by assaying live viruses.
Step 2: Gather Your Materials
The Toast Tester is a very simple build requiring only a PM2.5 sensor, Lipo battery, ESP32 microcontroller and power boost. The sensor I choose was nice as it displays values above 1000--many do not. Most of these PM2.5 sensors have been well studied for their accuracy and are good. All the components were carefully chosen for the bespoke case design printed in PLA.
1. PM2.5 Air Quality Sensor and Breadboard Adapter Kit - PMS5003 Adafruit $40
2. Lipo Battery 700 mah $4
3. TTGO T-Display ESP32 CP2104 WiFi bluetooth Module 1.14 Inch LCD Development Board $11
4. PowerBoost 1000 Charger - Rechargeable 5V Lipo USB Boost @ 1A - 1000C Adafruit $18 --but you can use generic for much cheaper
5. NeoPixel Stick - 8 x 5050 RGB LED with Integrated Drivers $6 Adafruit
6. On-Off Power Button / Pushbutton Toggle Switch Adafruit $2
Step 3: 3D Printing
The body of the Toast Tester was made in three parts. All are printed in PLA without support. The back case is designed to snap into position. The front dog nose is glued on with superglue. Make sure you align up the nostrils with the input and output holes for the sensor as it samples the air through these holes.
Step 4: Wiring It
The wiring for this device is fairly easy. 152