Industry grade equipment have different safety measures while the cheap equipment you get from aliexpress would be lacking in every aspect, better to practice safety than end up a kfc.
Besides, using a flammable solvent isn't recommended if you're a hobbyist. But if you insist in using it you can isolate it in a separate container which works well for small pcbs.
By experience, it seems the probability that ultrasonic could 'explode' alcohol solvent is almost diminish.
I have never watch its ever happened in my whole life.
The probability of static electricity on gas station to burn gasoline seems higher, since i could find lot of video of it.
The probability of Hydrogen explode on H20 electrolysis also higher, since i could find a lot of video of it.
The probability of Lithium battery explode is higher, i even experience it myself. The drone battery spontaneously explode.
Alcohol, even if you intently burn it, theres no explosion, only flame. Sometimes i play this kind of thing.
But instanteously alcohol 'explode' because of ultrasonic wave, thats i have never watch until now.
I even intently want it to happened, but it didn't. Its so difficult to spontaneously explode alcohol, only using ultrasonic.
Even make it spontaneously burn (not explode) using ultrasonic is seems impossible.
Spontaneous explosion is the least thing i ever worried, on using alcohol on ultrasonic.
The probability was so small.
Maybe using a huge power of piezo transducer to generate the ultrasonic, might induce the spontaneous burn.
But using the 'normal' cleaning piezo, it almost never happened.