Liquid Submersion Indicator location

I have a model a1466 EMC 3178 macbook air. I work for a school system and it is a school owned computer. I have a issue with users that have a spill then will not put that info on a work order. When I go to check it out I find the liquid stains on the inside. I have one that come in and due to it being dead I suspect it, the usual won’t start up type stuff. But inside I found no sticky residue or stains. So I was wondering where the sensors are placed to confirm the issue?