The dose makes the poison. The LD50 for lye is 4,090 (rats) - 6,600 mg/kg (mice). The LD50 for fentanyl is 3.1 mg/kg in rats and 0.03 mg/kg in monkeys. So, very different.
The only way someone is ingesting that accidentally is if a classmate is attempting to poison them. There are a lot of other poisons that can be ingested in small doses if someone is trying to injure you. Fentanyl is not going to leap out of someone's pocket and fly down your throat. It's not magic killing dust.
Accidental drug dosing happens all the time, with things with much larger effective doses. People mix up drugs. Drugs absolutely fall out of people's pockets on a near constant basis.
