My Norelco trimmer instructions say:
“Do not operate, charge or plug in Trimmer outdoors or where aerosol (spray) products are being used or where oxygen is being administered.”
Most electric motors are subject to brush sparking, especially if the brushes or commutators are worn. Flammable aerosols may be ignited by these sparks. They do make some intrinsically safe motors, but most are not.
Exactly. Creating sparks where a possibly alcohol-based aerosol cloud of indeterminate volume is being created - what could possibly go wrong? Also, oxygen in much high concentrations will cause flash fires (if exposed to a spark) where fires may not have started otherwise. Ever seen a demonstration of blowing oxygen on a burning object? (Hint: What does a dog say?) A higher concentration of oxygen lowers the flash point of anything significantly.
So the easy part’s answered. But what about outdoors?
I don’t know what kind of Trimmer you are asking about, but it’s likely not waterproof - they don’t want you to use it where it might get wet.
Since the OP said Norelco, I would guess a beard trimmer. But unless it’s raining, there’d be a greater chance of getting it wet in the bathroom than outdoors.
The power cable is not ruggedised … outdoor power cables have a stronger outer layer.
Per the OP it’s rechargeable. It wouldn’t be plugged in while being operated.