It is uncertain exactly what the temperature should be within the range of 60C-90C. However, if a temperature is selected, the process should be repeatable. So therefore if it is established that, for example, 70C is a good temperature, the device should keep the temperature within 68-72 C, so that others who use the same value will get the same result. It is not that any temperature within 60C to 90C will work best. So for example, I currently have written the software to allow for seven settings: 60 C, 65 C, 70 C, 75 C, 80 C, 90 C, 100 C. Also I have seven time delays: 10 minutes, 20 minutes, 30 minutes, 45 minutes, 60 minutes, 90 minutes, 120 minutes. It is important that the device produces repeatable results. Once the device has been programmed with a particular temperature and time interval, one should just ideally have to load the chamber and press a button and the alarm goes off when its done.
The problem is that different masks from different manufacturers may be able to tolerate different temperatures. For example, one mask might tolerate 90 C for 20 minutes, and so many could be disinfected quickly, while others might be more fragile and require 60 C to 120 minutes. There will be some variation in the controls here.
Also, I would prefer if the operations of controlling the heat and time were performed together. The people using this will probably not want to mess with it. They want to press a button and have it work. The less you give them to think about, the less that can go wrong. But if Arduinos are not available or local hobbyists are not available to build a circuit, having an oven timer and oven thermostat is definitely ok, but I am afraid that with all of the chaos going on in healthcare settings right now, the less that has to be messed with, the better. You can not underestimate the things that can go wrong in a healthcare setting especially when there is chaos, people are overworked, and there are emergencies popping up constant and tons of distractions. There must be as little to go wrong a possible.
A fan may be required to equalize the temperature in the chamber if the chamber is large.
I chose wirewound resistors at first (for example, 8 ohm audio loads), especially because low voltage could be used, reducing the electrocution hazard. However, I am more confident that light fixtures and incandescent bulbs are more widely available, hence my suggestion to use these as a heat source. I think they are also safer as well, as the surface of the bulbs usually doesn't get hot enough to ignite wood or other materials.
So a higher cost electronic device, if off-the-shelf, that could control the temperature within the ranges given, and be self-timing, would be best. So far I have found stuff for brewers and electric roasters.
So that's my reasoning behind this device. The attached document describes the circuit and project so far.