OH CR4P!

The U.S. Census Bureau estimates that the United States makes over $230 million of fireworks each year, and imports $190 million more. A large portion of these products are expended during the week of the 4^th of July.

(<-- Credit: 500gramfireworks.com)

But if those numbers don't surprise you, these others might: in 2011, 65% of all fireworks injuries occurred within the 30 days surrounding the 4^th of July. Over half of these were due to either unexpected ignition or improper use (e.g. shooting bottle rockets out of your hand). Many of these injuries are minor, caused mainly by sparklers, firecrackers, or small aerial products.

However, these thrills aren't enough to satisfy veteran firework consumers, and this is where things get hairy. Many people every July 4^th holiday get their hands on professional-grade fireworks. If those bad boys aren't enough, some DIYers may even make their own homemade rockets and mortars. Sounds like a fun time, but not for those who forget that what they are playing with is still a dangerous explosive. In 2011, four were killed because of these types of fireworks, and an estimated 9,600 more were injured.

Most of these accidents are the result of faster-than-expected explosions and the unintended flight paths of aerial fireworks. But does that mean that manufacturers or designers are to blame? Let's take a quick look at the composition of the standard aerial mortar used in professional displays. We'll use the diagram by Popular Mechanics (shown right) as a guide.

Fuse - All fireworks contain some type of external and internal fuse which provides the time delay between initial ignition and launch. Simple manual fuses are just rolls of lightweight paper filled with loose gunpowder. More modern fuses and launching systems involve electric matches, which allows remote ignition and sophisticated timing configurations.

Stars - Aerial fireworks contain small spheres called stars. These black powder coated spheres contains the mix of pyrotechnic compounds used to create the bright colors and visuals. The arrangement of these stars determines the shape or pattern of the resulting explosion.

Bursting charge - The stars are contained in a much larger paper shell filled with a bursting charge. The bursting charge is an explosive mixture of black powder and other chemicals which is ignited by the fuse.

Lift charge - A separate compartment of black powder below the shell is called the lift charge. This section is connected to the external fuse and provides the initial explosive launch out of the mortar tube.

Here's another picture from Popular Mechanics showing the cross section of a 6-inch cylindrical shell.

With so many variables in the design that could go wrong, it's important to realize that not every firework product will work perfectly. However, the fault for most accidents can't be put on those who made the fireworks, but on those who used them. Licensed professionals who conduct fireworks shows typically have elaborate firing systems, electric matches and/or timing devices to precisely control ignition and ensure safe launch. Even with these in place, some accidents can still happen. Those who choose to use professional grade fireworks without professional equipment or experience must assume the risks that come with it.

On the consumer level, however, almost all potential injuries involving defective fireworks can be avoided through safe, common-sense practices. This includes making sure the launcher or fireworks being launched are secure and stable, not relighting a failed fuse or dud, making sure the launch area (and area above) are open and clear, and making sure spectators are a safe distance from the ignition spot.

So whether you're going to see a fireworks display or setting off your own show this holiday, please be safe rather than sorry. A few more sparkles are not worth a few less fingers.

References

Fireworks - How Stuff Works

Fireworks Safety Infographic - CPSC

Five Fantastic Fireworks Facts - Live Science

How Fireworks Work - Popular Mechanics