The hang time, or persistency of the smoke effect produced by all artificial smoke systems is a function of some key factors:
The higher the boiling range and lower the evaporation rate of the smoke chemical, the greater the smoke persistency.
Generally, within chemical groups, the higher the viscosity and surface tension, the higher the boiling range.
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.
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.
Concept have introduced a Hang Time Index which 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 the ViCount type system 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 Concept’s most persistent water based smoke, (eg Colt 4 ,Spirit 900A) 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 Colt 3 or Spirit 900B 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.
Smoke Type: | Hang Time (20°C) | Index |
Food Quality Oil Based Smoke Concept ViCount |
3 - 4 hours | 10 - 12 |
Persistent Water Based Smoke Concept Colt 4 / Spirit 900A |
1.25 - 1.5 hours | 4 - 6 |
Quickly Dispersing Smoke Concept Colt 3 / Spirit 900B/AirTrace |
2 – 4 minutes | 0.17 |
Typical "entertainment" smoke system | 15- 20 min | 1 |
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> view all"We have used the two Spirit 900 smokes machines every day for the past two months during our "Rapid Intervention Crew" training. Both machines have proven to be very reliable and produce quickly the required volume of smoke. I would highly recommend these machines for any fire department use in any application."
Assistant Fire Training Officer