Creating an Atmosphere

Architecture, decor, furnishings, floor coverings, fittings, tableware, acoustics, background sounds, music, staff attire, lighting and even smells, number amongst the myriad of factors that combine to give a venue its own special sense of atmosphere. Not least among these factors is the very atmosphere itself. In less enlightened times, atmospheric ambiance was provided for us by our patrons, as they smoked themselves, and everyone in their vicinity, into a risk of respiratory disease and reduced health. Nevertheless, the image of the "smoke-filled bar" remains as an integral part of the culture we see portrayed in books, films and television.

Whether or not you want to your rooms to have the feel of the Cotton Club in the 1930s, without something hanging in the air, many projection, lighting and laser effects simply don't work. There are a vast range of atmospheric effects available, each with its own applications, advantages and problems. Although generically referred to as fog and smoke, the most common effects can be categorized into four main types: smoke, haze, fog and low fog. There is also a water mist effect that is currently only used outdoors.

Smoke can be produced by burning anything from frankincense to car tyres. Despite its ongoing use in the worship practices of many faiths, the indoor use of smoke in public places is not intrinsically safe. Whilst not all smokes are toxic, most smokes contain carcinogenic (cancer causing) agents and all smokes can produce respiratory irritation. In well ventilated situations, such as open outdoor spaces, smoke can be a safe, cost effective, and spectacular effect. Unlike fog, smoke can be produced in almost any colour, by burning the appropriate mix of materials. However, most coloured smokes are toxic.

Hazes consist of very finely divided particles, so small and light that they hang suspended and almost invisible, in the air for prolonged periods. Haze is a great effect for giving a solid look to the beams from lasers, followspots, mirror balls and moving-beam effects lighting, without substantially reducing visibility in a room. It is an ideal effect for creating a subtle atmospheric ambience. Haze machines use very little fluid to maintain their effect.

Fogs are clearly visible clouds that hang in the air for a some minutes before either settling or vaporising. Fog works well with strong beams of light, to create volumes of coloured space on a dance floor or a stage. Effects such as laser cones, gobo patterns and light tunnels work well with a moderate level of fog. Like haze, fog comes in only one colour - white, regardless of the use of colouring agents in the fog fluid. If you need coloured fog, the colour must come from the light that is illuminating it. If overused, fog can become a hazard for visibility and safe movement. However, shutting off the fog generators will allow it to dissipate within a few minutes, particularly if the air exchange system is operating efficiently. Fog machines require moderate quantities of fluid to maintain their effect.

Fogs and hazes are aerosols containing microscopic droplets of liquid. That liquid can be either a light-grade mineral oil, water, glycerine, a mixture of glycols (a family of non-volatile alcohols), or a cocktail of glycols and water. Whilst water is the cheapest, and least controversial of these liquids, it is also the most volatile, and so dissipates most rapidly. Glycols have been widely used for generations, in everything from food production to cosmetics and anti-freeze. Adding glycol to water slows its rate of evaporation, but using all-glycol mixtures produces longer lasting, and visually denser fogs.

In the concentrations found in fogs and hazes, glycols produce virtually no reactions on the skin or in the respiratory system. Of course, all fog fluids come with Material Safety Data Sheets that provide detailed information on the effects of exposure to their contents. Overseas research, in particular work by the US Entertainment Services and Technology Association on Broadway musicals, has produced recommended maximum exposure levels for fog and haze effects that are compatible with working in an environment where atmospheric effects are in constant use. Even opera singers, a group notoriously fastidious about what they breathe, are willing to sing in the midst of modern fog effects.

The fine droplets required for fogs and hazes can be produced by several methods, and it is these methods which serve as the major distinction between varieties of effects machine. Heat based machines, which are the most commonly available systems at the moment, inject a stream of fluid droplets into a heated chamber where they are vaporised. That hot vapour is then ejected from the chamber into cooler air, where it condenses into the tiny droplets that constitute the fog or haze. The exact mix of materials in the fog fluid governs the temperature required in the heating chamber for proper vaporization to take place. The pressure at which the fluid is injected into the chamber has a direct effect on the volume of fog produced, and allows this type of machine to produce variable amounts of fog.

Use of the wrong fluid mixture can result in either incomplete vaporization (characterized by a spray of fluid issuing from the machine instead of fog), or the partial combustion of the fluid (characterized by a small amount of wispy smoke coming from the machine). Neither of these results is particularly useful, and can damage the machine by clogging its plumbing or damaging the heat exchanger.

Cracker systems work by driving large droplets of fog fluid or water through a mechanical process that breaks the drops down into the micropsic droplets that form a fog or haze. These machines use no heating process and are therefore available for instant use. They consume only small amounts of fluid, but generally do not produce large volumes of fog or haze. Cracker systems are widely used for haze production.

Ultrasonic fog systems use high frequency sound waves to agitate a fluid and produce microscopic droplets immediately above its surface. These droplets are then driven out of the machine to be used as fog. Although almost silent in operation, this type of machine is not currently in wide use.

Low fogs are clouds of heavy vapour that cling to low areas and settle or evaporate quite rapidly. They give the sense of being in the cloud tops, or moving through a mystical landscape, and have the great advantage of dissipating almost immediately after the fog generator is turned off. Most low fogs are produced using hot water vapour and cryogenic materials such as Dry Ice or liquid Nitrogen to keep the fog low and to prevent the water in the fog from evaporating. Other low fog systems use a chiller unit, such as a refrigeration plant, to cool the output from glycol-based fog generators and thereby keep it low lying. Low fog machines use substantial amounts of cryogenic coolant and/or fog fluid, and can be expensive to run for long periods.

Specific precautions need to taken when using cryogenic low fogs for more than a few minutes. The Nitrogen and Carbon Dioxide contained in these fogs tends to accumulate in low-lying places, displacing the normal breathable air. It is important to ensure that nobody occupies these low places for prolonged periods. This is critical where there are multiple floor levels, such as chill-out areas or orchestra pits, or where over-enthusiastic revellers may decide to roll around in the fog gathered around their feet.

Some fire detection systems are unable to differentiate between the droplets of a safe non-flammable atmospheric effect and the smoke particles produced by a fire. Precautions need to be taken to avoid nuisance triggering of "smoke" detectors, without compromising the fire safety of a building. Fire system engineers should be consulted wherever atmospheric effects are to be employed, even on a casual basis.

In addition to leaving minute deposits in the respiratory systems of patrons and staff, atmospheric effects have a serious impact on the maintenance regime in the places where they are regularly used. In addition to the risks associated with the of pools of slippery liquids that may accumulate in the immediate vicinity of an effects machine, everything in the room will acquire a coating of the fluids used for the effects. Paintwork, drapes, air conditioning filters, fittings, furniture, glazing, etc, can be treated as if they were coated in kitchen grease. Mechanical and optical equipment requires special treatment.

The reflectors, lenses and LCD panels in all projectors and luminaires require cleaning with an agent that will remove the deposit in question, whilst at the same time not damaging specialised optical coatings. Mechanical systems such as the moving parts of lasers, lighting effects and moving lights, and the internal cooling fans on everything from sound equipment and video processors to lighting consoles, computers and any kind of projector, need to be de-gunked regularly, to prevent premature failure.

The reliability and relative safety of today's atmospheric effects have seen them become an integral part of many leisure and recreational activities. However they're not something that can be introduced, without careful consideration of their economic, operational and safety implications.

by Andy Ciddor, © Copyright The Kilowatt Company