Q: I train at home and I don't have a spotter. Is it safe to bench press alone?
Short answer - NO.
The barbell bench press requires a spotter or a power cage for obvious safety issues. It doesn't matter if you bench 90 pounds or 290 pounds - if the weight is demanding for your current strength level you should always bench with a spotter or in a power cage with the safety pins ready to catch the weight in case you can't complete the rep.
Believe me, you don't want to have a heavy barbell resting on your chest. Also if you experience some muscle cramp or some kind of a sudden and unexpected shoulder, elbow or wrist strain you might lose balance and before you know it the bar will be on your face. I've been in similar situation. I was doing a heavy set of 5 without a spotter. However I was benching with the safety pins set right below my chest. I did 2 reps and the weight turn out to be heavy for a set of 5. Anyway I did the most stupid think I went for another rep. I got the bar over my chest but at some point my triceps and front delts just left me and I lost the bar. It just crashed on the safety pins - right over my throat. As far as I remember I was benching 180 pounds at this time. But in this situation the weight is irrelevant because when you can't do another rep - you can't get the bar away from you. Even if your working weight is 90 pounds you can still hurt yourself. So don't be stupid and find a reliable spotter or bench in power cage with the safety pins just below your chest in order to be able to do a full range bench press BUT at the same time the safety pins should NOT be lower than your throat or face because you want to be able to safely lower the bar in case of emergency. Don't be an idiot and don't do stupid shit.
Watch the video below in order to understand how to set the power cage during a bench press workout.