A lot has changed since Ed Vanasek lit fireworks by hand 25 years ago.

In the old days, they’d bury 10 or so metal tubes — called “mortars” — in the dirt and light each of them by hand.

It wasn’t as safe as the modern method of letting a computer do the dirty work, but he never got hurt badly.

Vanasek, his wife, Shari, and two others spent Independence Day in a Minnesota State University parking lot under a hot sun, first assembling rack upon rack of mortars, then doing the electrical work to ensure they all go off.

Here’s how he describes the behind-the-scenes work that makes all those ooo’s and ahhh’s possible:

First, the racks with mortars of various sizes are set up, row by row. Some are angled to the left or right, to spread out the show and prevent the effects from mixing.

In the industry, the explosive power of a firework is measured by the diameter of the mortar needed to launch it.

For Mankato’s fireworks, the tubes are between three and six inches wide. Mortars more than two feet wide are used in some displays, but due to the location — occupied buildings are too close — six inches is the biggest they’re allowed to shoot.

The fireworks themselves (most of which seem to be slightly larger than a fist) are individually loaded into each mortar with a wire attached.

Each firework actually has two fuses.

The first one, only a tiny fraction of a second long, triggers the gunpowder-like material that propels the charge skyward. The second ignites the charge and explodes the firework.

The length of the second fuse is determined by the size of the firework. The rough rule is that for every inch in diameter, the firework should travel 100 feet in the air.

Nearly all of the fireworks have smaller charges attached to them.

One type, a mixture of chemicals, provides a high-pitched whirring noise. Another type provides the smaller, trailing explosions often seen as a firework shoots skyward.

Very few fireworks are alike; there are hundreds of varieties with suggestive names like “gold glitter crown” and “silver bowtie.”