Happy Bitey Snake

Frequency

First of all, I want to talk about something everyone knows about him: his quirk is potent enough to shatter glass. Now, when it comes to decibels, it's always important to consider the time and distance a certain note is held for, since these can impact the "hit" a certain sound wave can have when influenced by effects such as the air or vibrations.

(Please keep this in mind for the reminder of this post)

When it comes to glass, however, it breaks almost instantly under the pressure of his voice. Our most constant example of this is the man's poor lenses, but there is a scene I'd like to talk about the most, it being he one where he completely shatters Shigaraki's tank.

One might argue that the glass was already weakened from Mirko's kicks, but that's honestly part of something that makes this so impressive to me; Mirko's legs are strong enough to straight-up rip a high-end Nomu's head clean off, yet this tank was tough enough to withstand two attacks from her - including her ultimate move - before starting to leak; and the fact she was heavily injured doesn't fly here, as we very clearly could see she wasn't holding back one bit.

Now, let's get technical.

According to Google, a normal tone of voice would be around 50 decibels, while the required to shatter glass would be a minimum of 105. For comparison, that's roughly the same volume as a jackhammer. Now, you might be thinking, "Oh, that's not so bad! Some singers can do that!" and you'd be right, but there's also some other things to consider. Allow me to explain.

Some singers can reach a pitch that can make glass vibrate enough for it to break, but I've personally only heard of this happening if the person has their mouth close to a smaller, empty cup, and even then the volume would be distributed around. Hizashi, on the other hand, was standing several feet away from this reinforced tank and was able to shatter it immediately, using the directional speaker around his neck to aim the volume. This would naturally require for him to hit even higher decibels, specially when you take into consideration that one's frequency must match the glass' for it to vibrate, which drastically increases when it's dampened. (Read next topic for more info on this)

And then there's his glasses which, like I've stated before, are the most common thing he breaks with his voice. Obviously, this is not directed and it's not a total shatter, but there is something to be observed; say, did you know the necessary volume for lenses to crack, when not being directly aimed at, would be that of a nearby shot from a highcaliber gun? That's roughly 140-170 decibels.

Harm factor

Boy, oh boy! I'm betting most of you were looking for this part when you clicked the read more, right? Look no further, I've got you covered, you just better remember what I mentioned before about distance and duration.

Hizashi's parents were unfortunate enough to have a mutant child that was born with his quirk already active, and I'm willing to bet a newborn doesn't have the slightest bit of control over a power as destructive as a sonic-powered voice, which immediately resulted in everyone in the room bleeding from the ears.

Sound-related ear bleeding is most commonly associated with a ruptured eardrum, which can happen at around 150 decibels and is about the same as a jet engine taking off. While a baby most likely unleashed his maximum voice power on the first breath, and it was enough to burst eardrums, I believe something like that would, thankfully, only develop fully after puberty, just like with non-powered people like us since, again, his quirk is a drastic intensification of a function and not a new ability altogether.

With that being said... The Finals Exam.

In this, Hizashi was standing very far and, even with the directional speakers, there were many obstacles in the way that kept him from landing direct soundwaves on the students. Regardless, Jirou's ears bled in less than 30 minutes being exposed to this.

This could have happened due to the fact that she has a hearing quirk, which would make hers much more sensitive, but let's study this, shall we? We don't have the exacts of what happened there, but the students are visibly uncomfortable upon the first soundwave, which would suggest it was at about 120 decibels upon impact (with 85 already being enough to cause damage to your ears) and being emitted even higher by him, considering distance muffles volume. Still, I think all that would be nothing compared to the scream he let out after those bugs started crawling on him, with how unfiltered that was.

With Jirou, it comes to no surprise this volume at this distance and time almost rendered her deaf, and realistically would take several months of healing time. How much do you want to bet Hizashi got a solid scolding from Shouta? I mean, it was supposed to be a challenge, but homeboy came this close to breaking her quirk.

Another thing I want to point out is that his voice is powerful enough to actually fucking launch people, and this only happens due to an event called acoustic trauma, basically meaning Hizashi can surpass supersonic levels. Although, it's important to note that this effect is caused mostly due to pressure and not so much as sound, so while it's not freakishly loud (about the same as thunder), it can still cause hearing and psychological damage.

! WARNING !

The following part contains graphic mentions of injury, and death. Do not proceed if these are sensitive topics for you.

Now, we look at the disturbing side of Hizashi's quirk. Buckle in, because it's a wild ride.

Remember what I commented earlier, about him having to hit even higher frequencies to be able to shatter Shigaraki's tank? First of all, as the doctor was sent flying, this qualifies as supersonic, but that's not all. To shatter such a protected tank, with liquid inside increasing the density, he'd have to hit over 200 decibels; which is considered extremely dangerous and most definitely fatal, as the threshold of pain is of 115-140 - this can cause damage such as crushed ear bones, ruptured lungs, or embolism. For comparison, this would come close to standing right next to a Saturn V Moon Rocket during launch, and is no longer considered a "sound" due to the vacuum.

With that being said, the man came very close to dying by Hizashi's hands (voice?) twice. Not only was he so close during the lens incident, literally being inches away from his face and in risk of getting his eardrums ruptured already, but if Mic had decided to raise his voice even more during his rage, it'd be possible for the frequency to make the doctor's inner organs malfunction, or straight-up burst from the pressure.

But that's not the worst part.

After establishing that the lethal amount of over 200 decibels would be necessary to shatter the tank given the circumstances, if he exceeded 240 and the doctor happened to be in the way of this, it would be enough to cause his head to explode upon impact. That old man better be grateful that he was standing a feet few away, and that the supersonic blast blew him away a bit more, or it'd be an immediate game over.

With all this being said, how devastating would it be for this guy to scream his rage out?