A day of devastation

I don't think so, it's basically baking soda with potassium instead of sodium. It will be stable until it gets wet or mixed with something acidic, but even then it won't produce any harmful by-products. You can use it in baking as a low salt alternative to baking soda.

Apart from being more effective, another reason it's used instead of baking soda in gardening/farming is that you don't want too much sodium going into the soil, whereas the extra potassium will benefit a lot of flowering plants.

I just weighed a tablespoon of my potassium bicarbonate and it was about 17 grams, so to be more precise, in a UK gallon that's a 0.37% solution which is well under what would be harmful to plants, and a lower concentration than I have used with no ill effects.

Armicarb is a fungicide used by organic farmers in Europe, and it's essentially potassium bicarbonate plus detergent and a wetting agent. The detergent is sodium lauryl sulphate, which is found in a lot of liquid hand wash.

I think it's likely that another ingredient in the hand wash is the culprit. My preference is unscented liquid castile soap, since it's pure soap and typically doesn't contain any other ingredients.