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


Confined Space Rescue Program Manager - North Tree Fire

ViCount use in Hot Fire Trainer

The machine has performed flawlessly up to this point and I purchased the machine from you at least six or seven years ago.

I have to confess I have never cleaned the orifice with the drill as you mentioned.

Actually, after the install, I have never worked on the machine again which, I am sure, is at least neglect on my part.

We originally had two smoke generators in the trainer, one fore and one aft.   The other machine (not Concepts) is quite a bit older
and it quit about two years ago but we found that the ViCount generated so much smoke we did not really need two machines.

The machine is protected from the heat of the trainer by a bulkhead with a port for the smoke to get through.

To give you an idea of the efficiency and quantity and the character of the smoke, the ceiling temperature inside the trainer as verified by two gauges reaches about 1300 degrees F. The smoke level inside the trainer is maintained quite adequately from the floor to about the
four and one half foot level but not much higher due to the temperature. We have found that it burns off at about 450 degrees F (230C).

Your smoke machine has trained hundreds of line Firefighters from all over the US including from major metropolitan Fire Departments such as Los Angeles County Fire, Pasadena Fire, San Jose Fire, Las Vegas Fire, Oakland Fire, Berkeley Fire, Sacramento Metro Fire, Cal Fire, and many federal agencies as well.

The training and experience those fire fighters receive in the intense heat and disorientingly smoky environment the ViCount helps create has without question saved lives and injuries as well as millions of dollars of property damage that may have occurred without the level of training
the ViCount helps provide.

Thank you for your help and support.

Best regards,

Mitch Ward CIHM
NorthTree Fire
Confined Space Rescue Program Manager