Smoke Hang Time Index

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.

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.

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

Demonstration movies

scroll through the slides,
click on a thumnail and
view the movies

latest news

Latest News

> view all articles

Colt 4 Twin Turbo - New Product

Concept Smoke Systems are one of the leading smoke machine manufacturers... Read more >

ESS 2015

Concept are pleased to be exhibiting and supporting the Emergency Servic... Read more >

> view all


Bekonscot - Managing Director

For several years we went through numerous smoke generators to simulate a "burning building", an important feature in our presentation.  Although the effect produced was good, the reliability, servicing and running costs of the system were always a headache, with smoke machines sometimes lasting a few weeks before they failed.

In June 2000, on recommendation, we contacted Concept Smoke Systems regarding the smoke installation.  A ViCount system was installed and commissioned later that year and has been operating without failure ever since!! Smoke chemical consumption has fallen dramatically, serviceability has been 100% and the effect is as impressive as ever.  Minimising issues relating to maintenance, and maximising reliability has given all of our visitors (some 200,000 per year) the benefit of seeing the smoke effect.

We wouldn't hesitate to recommend these systems to other users who need reliable and cost-effective smoke!