If the concern is that the glycol vapor may hit the hot light bulb in the oven and be ignited, let me describe a little experiment. Cut a 1/2 inch wide strip of paper towel or toilet tissue long enough to reach from top to bottom of the perforated grill that covers the bulb and tape an end of it at the top so you can see the direction of airflow through the grill by the angle of the dangle. Put a cup of water in the oven to prevent overloading the magnetron and turn the oven on for a few seconds. You will see that the flow is from the bulb enclosure INTO the oven. Neither the direction of that flow nor the flashpoint of the liquid being heated will be an issue if no vapor can leave the container of glycol. There are several brands of plastic cling wrap that are microwave safe. It is a simple matter to cover the container of glycol so that vapor does not escape from it, nor is there a chance of a spark entering the container. Leave enough slack in the plastic wrap so that some part of it lies on the glycol surface after it is sealed. You will see that it does not leave the surface until the vapor pressure of the glycol exceeds the atmospheric pressure, which happens at about 370 degrees F where it begins to boil. You can test this with plain water in a pan on a stove top. The plastic wrap will lie on the water surface until the water begins to boil. There is no need to reach the boiling point of water, much less the boiling point of glycol, and certainly not that of TEA. 150 degrees F (66 degrees C) are more than sufficient to speed up the dissolving of the chemicals in any of the developers that use glycol or TEA as solvent. That is well below the flashpoint of either propylene glycol or TEA. It is a simple matter to test an individual microwave oven in steps to calibrate it for these solvents. My microwave heats 500 ml of propylene glycol from 70 to 150 degrees F in 1.5 minutes at highest heat.