The factors that shift the sound of fireworks from deafening to delightful
For as much as he enjoys making noise himself, my four-year-old is not a fan of loud noises. The Fourth of July is a stressful holiday, since he like the dazzling colors of fireworks but is very sensitive to the booming explosions created by a professional show. As much as we try to reassure him that there’s nothing to be worried about, he’s not entirely off-base to be worried about the volume levels of large fireworks— the World Health Organization (WHO) recommends that kids not be exposed to sounds more than 120 decibels (dB) to avoid hearing damage. Depending on how they’re made, some fireworks might be as loud as 150 dB, so how can we take our kids to see, and hear, these explosions in the sky each year?
How bad is that boom?
To make sense of this, it’s good to know what’s happening when you hear a loud ‘boom’ in the sky. When a firework shell explodes, the heated particles and gases expand outwards with immense force, slamming into the air molecules already in the sky. The exploded particles push the air outwards, compressing those molecules into a pressure wave moving faster than the speed of sound. That blast wave continues expanding in all directions at once. This is important, because it means that the initial energy of the explosion is being spread out more and more the further outwards it travels. If you’re a reasonable distance away, you’ll only be hit by a portion of the initial explosion’s energy, rather than the whole thing. So a firework that explodes at 140 dB will only reach you at 93 dB if you’re 200 feet away. Most professional fireworks explode at higher altitudes than that, reducing the amount of energy that ever gets to your ear.
This can still be a significant amount of energy though. If you’ve watched a professional fireworks display you’ve probably felt at least a bit of pressure on your body as the wave of knocked air particles slams into you. This may have felt more or less intense depending on the state of that air before the explosion. Humidity helps carry sound, and pockets of cold air below warm air carries blast waves better as well. Back-to-back explosions don’t actually boost each other’s power, but the repeated sounds are perceived as louder to our ears.
In addition to distance from the explosions, timing is important too. Brief exposure to loud sounds isn’t nearly the problem long exposures are. Even if you did hear a 120 dB explosion, your hearing would most likely bounce back to normal, while spending eight hours listening to 87 dB noise could leave you with permanent hearing loss. This isn’t to say that listening to explosions is necessarily pleasant for your ears, as you might experience short-term hearing loss after really loud sounds, but that chances are the firework show won’t last long enough to really be reason for concern.
Deafening by design
The last element to consider is that not all fireworks are created equal. Most professional shows are only punctuated by loud booms and crackles, partially to avoid overwhelming the audience with a wall of indistinct noise that wouldn’t be fun. The loud fireworks are known as salutes, and they actually boom by design. Just as pyrotechnicians use knowledge of chemistry, physics and geometry to create cool colors and patterns in the air, they can also choose to make a particular shell noisier or quieter. For some people, the booming noise is actually a priority, and they work to create louder, more concussive blast waves. The pinnacle of this design theory is the Gabe Morte, or “dead head,” which actually skips the pretty lights altogether to focus on entirely on the size of the sound. Obviously, my four-year-old will be passing on anything following the “thump junkie” school of thought, but hopefully he’ll be able to enjoy the quieter shows most of us enjoy on the Fourth of July… from a reasonable distance.
Source: How Loud Are Different Fireworks? by Kris Zambo, Dynamite Fireworks
