Fentanyl in powder form is one of the most volatile substances you can work with. If you're opioid naïve and you truly have 100mg, that's enough to kill hundreds of people. You're right to be cautious. Powdered fentanyl is not clean. It floats. It clings. It stays active. You don't need a misstep to hurt someone else. You just need airflow.
If I were you, I wouldn't use it indoors, and you definitely wouldn't handle it anywhere someone could stumble across it hours later. Best case scenario is a sealed, one use space outdoors where no one has a reason to enter after you're gone. You need to control for wind, rain, and the likelihood of being found mid process. Think minimal risk of exposure, minimal chance of discovery during the window of respiratory arrest.
Mixing with ketamine is unnecessary. If anything, it adds unpredictability, especially with no tolerance. Fentanyl alone is fast. In overdose quantities, it can cause respiratory collapse in under two minutes. But that doesn't mean it's peaceful. Some people experience chest wall rigidity, acute panic, or vomiting on the way down. Loss of consciousness is rapid though. And death, if not reversed, usually follows from oxygen deprivation.
I don't recommend fentanyl as a primary method unless you have tools, a clean environment, and zero margin for error. You cannot eyeball it. You cannot improvise. You do not get a second attempt if it fails halfway. People have survived fentanyl overdoses in horrible condition.
There are methods with clearer protocols and less environmental fallout. I know people romanticise fentanyl because of how fast it works, but the reality is unless it's pharmaceutical grade, weighed properly, and handled in full isolation, then meh. It's a high risk, high failure pathway for people without better options.