How Does Hollywood Make Explosions?

Movies aren’t like real life. Showing up outside your ex’s place at 2 a.m. is stalking, not romantic. If you start singing in a restaurant, the other patrons won’t join in—with a dance number to boot. And cars don’t explode all the time.

Actually, most things don’t explode very often. And when they do, they look very different from how they appear in Hollywood movies. Let’s dig into the world of special effects.

What a Real Explosion Looks Like

Real explosions don’t look very much like Hollywood explosions. When a high explosive like TNT is detonated, there’ll be a bit of a flash and a lot of dust, but not much in the way of flaming clouds. Most of the destructive energy goes into an almost-invisible pressure wave. It’s this that does the damage, knocking down walls and flipping cars. You can see a real explosion in the clip below from the Discovery TV show, Mythbusters. Here, they’re setting off 850 pounds of ANFO (ammonium nitrate/fuel oil), and, in the high-speed footage, you can see the blast wave traveling faster than the speed of sound.

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A near-invisible wave of destruction isn’t particularly photogenic, so Hollywood has to amp it up to look good on film.

Also, real explosions are very, very dangerous. Moviemakers want to get the biggest bang possible—without anyone dying or destroying a city block. The explosion has to look dramatic, but it can’t be that dramatic.

Practical Effects

Hollywood explosions have to look the part. A loud bang, a dust cloud, and lots of instantaneous destruction just don’t give the main character much of an opportunity to drop a good one-liner. Instead, most movie explosions are slower with dramatic fireballs that look destructive, even if they aren’t. After all, an action movie is only as good as its biggest explosion.

To get the flames, pyrotechnicians do the obvious: they use lots of stuff that burns. Flammable liquids like kerosene and gasoline are popular, as are dry powder mixes. The largest movie explosion ever, from the James Bond movie Spectre, used 8,418 liters of fuel and only around 70 pounds of high explosives. It makes a big enough bang, but more, it makes a mighty fireball.

https://www.youtube.com/watch?v=YAg_jqthRY4

To get the other visual effects of explosions, like car doors and people flying through the air, Hollywood fakes it. To throw physical objects, special effects departments often turn to air mortars. These use compressed air to launch whatever’s needed, whether it be debris, blood, or a truck, into the air. Since the amount of pressure applied can be controlled precisely, they’re much safer than explosives.

When people need to go flying through the air, the stunt department is called in. Stunt performers regularly use small trampolines (that are digitally removed in post-production) or wires to jump into the air. By timing the explosion with the stunt performers leaving the ground, it looks like the force of the blast threw them up.

Going Digital?

Most big blockbusters still use practical effects for explosions for a couple of reasons:

• It still looks better. Audiences can often tell if something is 100% CGI, especially when it’s a closeup.
• Stunt performers have an easier time reacting to physical effects than a cue. They’re often what sells the best explosions.
• It creates buzz for the movie. Audiences still love knowing there are physical stunts. It’s always big news when a star, like Tom Cruise, does their own.

https://www.youtube.com/watch?v=ent02yItm60

With that said, physical explosions are almost always enhanced with CGI in post-production. Wires, mortars, trampolines, and more are edited out, while extra flames and bigger dust clouds are added. In the video above, you can see how Mad Max: Fury Road uses mostly physical effects that get amped up in post.

And that’s how it’s done: a mix of clever CGI, crazy stunt performers, and lots and lots of flames is what makes a Hollywood explosion look so good—without blowing any unintended doors off.