I know the answer to this (I think) but wanted reassurance / back-up / ammunition...
At the weekend my dear partner managed to spill some fluidy stuff he puts in the petrol tank of the car to clean the injectors (or some such) over our son's (20 mths) car seat. Aside from smelling bloody awful and rendering it, at the very least, temporarily useless while it was comprehensively washed, it has melted sections of the polystyrene that's packed into the grooves in the seat under the upholstery. In my book that's not safe now, but he's says polystyrene is not 'structural' and it's fine.
Anyone have any thoughts?