Technology: Atmospheric effects
Technology: Atmospheric effects
Elation Professional’s Bob Mentele sheds some light on a foggy subject
We’ve become accustomed to the use of atmospheric effects in various types of entertainment. Think of those big, sudden bursts of fog that quickly envelope everything around it, enhanced by the creeping blanket of smoke that makes its way leisurely across a stage, accented by a fine, smoky haze that fills a room and highlights every single beam of light.
The use of fog, smoke and haze effects has become so common, and the technology has been made so affordable, that any amateur hobbyist can purchase an inexpensive machine at their local big-box retailer. It takes many different pieces of equipment to achieve the overall effect.
Types of atmospheric effect
Let us first investigate the different types of atmospheric effects and what types of machines we can use to create them. We often use the various names of atmospheric effects interchangeably but there are distinct differences between them. First, smoke is the byproduct of the combustion process and is composed of solid particles that are released into the air during a combustion reaction. We can only create this effect with the use of fire, combustion through a pyrotechnic material or prefabricated smoke cartridge. Because this effect requires fire or combustion to be involved in its creation, we will rarely see it in live performance situations due to the additional hazards it poses. When it is used, a certified pyrotechnician is required. Luckily, we have safer methods available to create the same effect.
Fog is a similar effect to smoke, but much safer to produce, quickly creating a thick cloud of white smoke. Some allow for variable output, so if a small amount is required over a long period of time, that can be produced as well. The effect is typically meant to be more defined and apparent than others. There are two methods commonly used to create fog, and the method used is dependent on what liquid is used in the machine. The first involves the use of a glycol or glycol and water mixture. The liquid is pushed into a heat exchanger by either a pump or a pressurised inert gas and travels through the heat exchanger until it gets hot enough to vaporise, but not burn. That vaporised fluid is expelled out of the heat exchanger, mixes with the cooler air and the vapour condenses in the atmosphere, causing a cloud or fog to be produced.
The second method is very similar to the first. The glycol-based fluid is replaced with a food grade oil, which is pushed through a heat exchanger, but, instead of becoming vapour, it is simply warmed. Through the use of pressure and heat, the oil is broken down into small droplets, which are expelled from the machine to create a cloud. One method is not better or safer than the other, they are just ‘different’. Typically, oil-based effects do have a longer ‘hang time’ and most use less fluid to create the same amount of fog than their water-based alternatives. Various effects can be obtained with the selection of different fog fluid mixtures. Some are made to hang in the air for a long period of time, while others are intended to dissipate almost immediately.
What if we don’t want to have a heated cloud of fog? How do we create a ‘low fog’ effect? There are a few methods. The first, and safest, is to use a fog cooling device. As its name suggests, it simply cools the fog. Fog rises because it is a hot vapour, which is less dense than the air around it, so is naturally lighter. If we contain the fog, and rapidly cool it before it dissipates, it becomes denser, or heavier, and is unable to rise, therefore staying low to the ground until it warms or is agitated by movement. The colder we can get the vapour, the lower it will hang to the ground and the longer it will last. The easiest method of cooling the fog is by pushing it through a container of ice as soon as it’s created. The melting ice does create water as a byproduct and our reliance on ice limits the duration of the effect. To get a longer-lasting output, we can use a chilling device that works similarly to an air conditioning unit. While we don’t have to worry about the ice running out, and having to drain a container of water, the unit does cause the fog to condensate inside of it, so some liquid is created. These devices also tend to be fairly loud because they rely on a fan to force air into the unit. In a similar device, instead of relying solely on air movement to cool the vapour, CO2 is used instead. This method creates a cooler environment to chill the fog and can create a longer-lasting effect. All of these cooling methods can be effective, but the pros and cons of each are something to consider.
Another common method of creating low fog doesn’t rely on a fog machine, but on water and CO2 in the form of dry ice. Dry ice fog takes advantage of the process of ‘sublimation’ or the changing of the solid dry ice directly into a CO2 gas when brought into a warm environment. In this process, the air around the piece of dry ice experiences a sudden drop in temperature, causing water vapour in the air to condense and form fog. We can accelerate the process and amplify the effect by heating a large amount of water and either submerging the dry ice into the water, or by using a pump to bring water into the ice chamber and pouring it over the dry ice. Either way, this process produces a large amount of water vapour fog which will cover an area in a very low cloud of fog. This method is more effective than using cooled fog because the water vapour gets much colder and heavier. You also do not get any visible dissipation like you will with a fog machine, although it can be dangerous. Dry ice must be handled properly, or it can cause serious harm. Additionally, CO2 gas is released into the air and if too much accumulates in a room, it can cause suffocation. In most large performance areas, this is not much of a concern for a temporary effect, but care should be taken in small spaces or if continuous output is required. Dry ice can also be expensive and hard to obtain in large quantities.
The last type of effect that we commonly see is haze. Haze differs from fog because it is intended as a thin, even layer of ‘atmosphere’ that fills an entire room. It’s not meant to obscure an audience’s vision but to enhance the look of the lighting or to make the room more gritty. Hazers are not typically used for short-term effect but are left running for long periods to provide a continuous level of coverage during an entire event. Haze can be produced similarly to fog but a haze machine will use a fluid specifically designed to hang in the air for hours on end. Haze machines come in both water- and oil-based variations and the process they use to create the haze is the same as with fog, only the fluid or oil usage is much less. To help the effect disperse, there is either a fan built into the machine or compressed gas is used to give the haze more momentum as it exits the nozzle. As for the differences between oil- and water-based machines? There isn’t much. Oil-based machines can be louder due to their reliance on a compressor to push the fluid through, but they typically produce a more uniform, longer-lasting effect. Water-based haze is much easier to clean up and oil-based haze can leave a lot of residual ‘gunk’ on equipment and surfaces when used in a space continuously. However, oil-based machines typically use less fluid than water-based. So again, there are pros and cons to each.
One consideration is the effect that the HVAC system in a room can have. Too much air circulation and you can have a hard time maintaining an even level of haze coverage; not enough and you can inadvertently fill the room too much. Low-lying fog is notorious for being affected by air circulation systems. Each room is different, and it can change as the room fills with people, or as the seasons change and you switch from using heat to air conditioning. When using fog, attention should be taken as to where air supplies and returns are located and if they blow the fog around.
Another system to be concerned with when introducing atmospheric effects into a space is the fire detection system. Every building is required to have a fire detection system of some type but the method that system uses to monitor the building can vary greatly. In any case, when an atmospheric effect is desired, you will want to find out what type of detection is in use. If there are particular sensors present, your effect may cause a false alarm. Water-based effects have a higher chance of tripping the detector, due to the size of the particles they produce, but even oil-based machines can cause issues with some detectors. If you have beam-type detectors in the room, any effect will almost certainly cause an issue. In any case, a system should never be disabled for a simple atmospheric effect. Work with your alarm company and local administration to find a solution.
One last area of concern that comes up is if the effects are safe to breathe. We discussed issues that can arise with CO2-based effects but what about oil- and water-based fluids? There have been numerous groups that have had this researched – when atmospheric effects are produced in accordance to a machine manufacturer’s instructions, using a quality fluid, no significant health concerns exist. Even the fluid themselves are quite safe to handle.
Adding an atmospheric effect into a system can greatly enhance the mood and feel of a service. And it can be easy to implement. The biggest job you have is to decide, based on your unique space and requirements, what machine is the right one for you. Remember to check the power rating of a fogger, which is typically expressed by the wattage of its heat exchanger. For a haze machine, you will want to know the size of the room you want to fill; the maximum output for a machine is typically measured in cubic feet per minute.
How do you want the new device to be controlled? Entry-level models are either ‘on’ or ‘off’ with no remote control or variability. Some models have a wired or wireless remote control. Most professional models have integrated DMX control that allows control from the comfort of your lighting console. Hopefully with this extra information, you can now make an informed choice and cut through the fog that may have clouded your judgement before.