General Artificial smoke is produced by heating a chemical above its boiling point
within a heat exchanger. The chemical is then vaporised, and it is when the vapour exits
the heat exchanger and mixes with the relatively colder atmosphere that rapid condensation
of the vapour takes place, resulting in a visible smoke (or technically fog).
It is important that the vaporisation of the chemical within
the heat exchanger is complete, otherwise the production of a 'wet' smoke, or a smoke with
a very large particle size will result.
Conversely, it is important that the heat exchanger through
which the chemical is passed is not operating at too high a temperature, otherwise
unpleasant and potentially hazardous pyrolysis products will be formed.
Types of Smoke Chemical
Water Based
The majority of smoke chemicals in use today are generally
referred to as 'water based'. This rather vague term describes chemicals which are water
miscible, and are in the main based on glycols and glycerol.
Water based smokes are dense and white, and the generators
that produce them, such as our Colt, can be simple to operate and very compact.
Typically two-thirds of the 'Smoke Chemical' is made up of
active ingredient, the remaining one-third being purified, de-ionised water.
Different Glycols produce smokes of differing persistencies,
Propylene Glycol generally being the least persistent. Glycerol is by far and away the
most persistent 'water based' smoke.
We would normally recommend that, where dense concentrations
of water based smoke are required (e.g. Fire Brigade Training, Leak Testing), that the
most persistent smoke possible is produced (like our Colt 4 or Spirit 900A). The use of
chemicals with high percentages of glycols, whilst producing dense white smoke, is not
cost effective, as the smoke disperses so quickly that one is having to produce smoke
almost all the time in order to keep up with the rate of breakdown of the smoke.
Glycol smokes begin to layer noticeably at 35-45°C,
Glycerine smokes at about 50-60°C.