Fog and Haze 101: A Primer

You’ve seen fog and haze used in movies, concerts, TV shows and theatre productions, whether you realized it was created with a machine or not. Steam from a tea kettle. Billowing smoke after an explosion. An airplane flying through clouds. The appearance of lasers during a magic show. These are all effects made possible by fog or haze machines.

But what exactly is fog anyway? How do you keep it close to the ground? What about haze? Can you make fog or haze in different colors? Are fog and haze safe? Here are the basics of fog and haze. Please hold your questions until the end of class.

Fog Basics

Fog is actually a collection of tiny liquid droplets that are suspended in the air, whether that fog is produced by Mother Nature or a fog machine. Fog machines create fog by vaporizing fog fluid. In other words, fog fluid is converted to an aerosol form, usually by forcing the fluid through a heated pipe at high pressure. This produces a thick, opaque effect that’s purposely uneven and lasts for a short time.

Fog is a smoke-like effect, but it’s not smoke. Smoke is made up of solid particles and created by burning something, while fog is made up of liquid droplets and created through vaporization. Fog fluid is heated during vaporization, but not burned.

Fog is typically used in live and filmed productions to create special events, from the appearance of cigar smoke from an ashtray to thick fog that obscures a huge battlefield after gunfire. 

Low Fog Basics

You can create fog that stays close to the ground by cooling it. This allows you to create the effect of walking on a cloud, add excitement or drama to a dance floor or stage, or make a swamp look spooky. 

The old-school method is to create low fog is to pour hot water over dry ice. But fog output is difficult to control and you’re left with a messy residue. You can also chill fog from a regular fog machine by putting a low-fog converter in front of it. Some machines use cryogenic liquid like liquid nitrogen to cool fog, but this releases gases into the air and potentially cause safety issues. More on that later.

We’ve engineered a single machine that creates fog and runs it through a large cooing chamber to keep it low to the ground. Fog fluid that creates fast-dissipating fog generally works best because the fog will evaporate before it warms and rises.

Haze Basics

Like fog, haze is made up of liquid droplets. Unlike fog, haze droplets are very fine and distributed evenly over a large area to form a mist. Some haze machines vaporize fluid by forcing it through a heater, while others use high air pressure to vaporize the fluid.

Haze is primary used for light enhancement. It makes lasers, sunlight, spotlights and other beams of light visible. Because light reflects off the droplets, you see light that you normally wouldn’t see as it travels through the air. Haze is also used to create a misty atmosphere and make a scene appear three-dimensional.

How to Make Colored Fog or haze

Fog and haze are actually clear. They appear white because the light they reflect is usually white light. The only way to get colored fog or haze is to shine a colored light on the droplets so they reflect that color.

You can also burn substances to create solid particles that are indeed colored, but that’s smoke, not fog or haze. Powder can also be dispersed in the air, but that can be messy. After all, what goes up must come down.

Please, please, please, do not put any kind of colorant, like food coloring, into your fog or haze fluid. It won’t create colored fog. Substances designed to create solid, colored particles will do nothing but ruin your machine. 

Fog and Haze Safety Basics

Fog fluids are generally made of water-soluble glycols such as propylene glycol. These glycols have been used for decades and health data on these substances is widely available. 

There is an American National Standards Institute (ANSI) standard that defines how much glycol a healthy adult can safely breathe (ANSI E1.5 – 2009 (R2018) Entertainment Technology – Theatrical Fog Made With Aqueous Solutions of Di- And Trihydric Alcohols). That said, we always recommend using the smallest amount of fog necessary to produce the desired effect.

As I mentioned previously, fog machines that use cryogenic products to cool the fog so it stays low to the ground add gases like carbon-dioxide and nitrogen to the air. Gas levels must be closely monitored to make sure they don’t reach toxic levels or cause oxygen deficiency.

Haze fluids are typically either water-soluble glycols or highly refined oils. The safe level for oil is different than that for glycols, but is still much higher than the amount typically used for haze effects.

There you have it – a 101-level primer of fog and haze for the entertainment industry. Have questions? Not sure what kind of fog machine, haze machine, fluids and/or accessories you need to create your desired effect? Give us a call at 1-800-426-4189.