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Smoke Hang Time

The hang time, or persistency of the smoke effect produced by all artificial smoke systems is a function of some key factors:

Boiling range and evaporation rate of the constituent chemicals
The higher the boiling range and lower the evaporation rate of the smoke chemical, the greater the smoke persistency.

Viscocity and surface tension
Generally, within chemical groups, the higher the viscosity and surface tension, the higher the boiling range.

Particle size
The bigger the particle size, the lower the ratio of surface area to volume, hence the greater persistency. However, remember, the bigger the particle size, the faster the settling velocity (ie more chance of residue being left on surfaces).

Ambient temperature
Generally, the higher the ambient temperature of the air in which the smoke is suspended, the faster the smoke will "evaporate".

Many smoke systems (largely those based on the entertainment industry requirements) produce a dense white smoke effect, but one that evaporates very quickly. Hence, although the initial burst is impressive, filling large volumes with smoke becomes problematical, as one quickly reaches the stage where the smoke produced a few minutes ago has evaporated, and smoke density no longer increases. Also, systems which quote a smoke output unqualified by smoke density or visibility are of no use when trying to make comparisons.

The hang time table below better allows a user to establish the relative performance of smoke systems, in particular with regard to large volume or extremely dense smoke concentrations.

Generally, oil based smokes, with their very high boiling range, will produce a smoke effect that lasts for an exceptionally long time. This makes our Phantom Oil Based Smoke Generators particularly suitable for smoke logging exceptionally large volumes, which would need perhaps 10 or 12 times as many high output water based systems to achieve the same performance.

For our most persistent water based smoke, we have selected a water miscible pharmeuctical grade chemical with the highest boiling range in its class, and used a very high percentage of this active ingredient in the mix. This gives the “Holy Grail” in terms of water based smoke of high persistency combined with the small particle size and hence insignificant settling velocity.

Where quickly dispersing smoke is required (localised air flow tracing for example) the PS21 or 2.2kW High Output Smoke Machine with smoke fluid B would be chosen, as the active ingredient has the lowest boiling range of the commonly used simulants.

Using the Hang Time Index in conjunction with quoted smoke output figures, (providing those figures are quantified in terms of smoke density or visibility) allows a simplistic comparison to be made of smoke systems.

This is particularly relevant with larger volumes or denser smoke concentrations, where the persistency of the smoke becomes of greater significance.

Fluid type
Smoke Hang Time (at 20C)
Oil based smoke system
3 - 4 hours
PS27 Type A, PS23, PS25
1.25 - 1.5 hours
PS27 Type B, PS21
2 - 4 minutes


Hand Portable Smoke Machine - units to deliver quick dispersing smoke (PS21) or long lasting (PS23). Off-power facility on basic models. 240/110v. (PS21, PS23 and PS25)
2.2kW High Output Smoke Generator - continuous high output 2.2kW machine with a choice of fluids available for either quick dispersing smoke or persistent. 240/110v. (PS27)
Oil Based Smoke Machine - oil-based smoke machines with continuous high output for large scale applications (see photo below). The generated smoke can withstand high temperatures. The units can also be re-programmed to accept water based fluids. 240/110v.

The Oil Based Smoke Generator in operation

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