by Dr. B.A. Colenutt
Uxbridge, Middx. UB8 3PH
Le Maitre smoke fluids are materials supplied by Le Maitre for
use in their smoke generators. A reservoir is charged with the water
based fluids which are forced by pneumatic pressure into a heated
chamber. Here the fluid is immediately vaporised and expands. On
passing into the atmosphere a mist or smoke is formed as a result
of condensation of the vaporised material.
A series of tests have been carried out on the two Le Maitre smoke
fluids and the smoke generated from them. The objectives of the
i) To confirm that the composition of the fluids were as stated
by the manufactures.
ii) To establish whether the water soluble organic components
were involved in any chemical reaction during smoke generation.
iii) To determine the nature of the products of any such reactions.
iv) To review the available evidence for the safety of the atmospheres
generated particularly in respect of individuals who would be exposed
to the atmospheres.
The experimental work primarily involved the technique of gas-liquid
chromatography. This is a sophisticated instrumental technique for
the precise analysis of mixtures of volatile organic compounds.
Mixtures are passed through a column in a stream of carrier gas.
Various components of the mixture move through the column at different
rates and thus the individual components arrive at the end of the
column at different times, that is, the mixture is separated. Column
effluent is monitored by a highly sensitive detector. The time of
passage through the column is characteristic of a particular substance
and the size of the signal from the detector is an accurate measure
of the amount of substance.
2. EXPERIMENTAL AND RESULTS
2.1 Le Maitre
2.1.1. Analysis of the Fluid
The composition of the fluid was supplied and these tests were
to confirm the composition.
Standard samples of the components propylene glycol and water
were obtained and an analytical procedure for their analysis was
developed. Details of the analysis are given in table 1. Although
the system should not produce a response to water there was in fact
an early peak attributable to the compound. This artifact is not
unusual and created no problem. Propylene glycol eluted as a symmetrical
peak within 10 minutes.
When samples of Le Maitre Smoke Fluid were examined a single large
peak was produced in the chromatogram the retention time coincided
with that of propylene glycol. When the sensitivity of the detector
was increased a second peak, which did not coincide with water,
became visible. This was, however, a minor component probably representing
less than 2% of the total. It was concluded that the propylene glycol
and water were the major components and further tests were carried
out on this basis.
2.1.2. Analysis of the Smoke Generated
The primary objective
of the analysis was to confirm that the smoke also contained propylene
glycol and that no products other than stated, resulted. Two series
of tests were carried out. One series examined the smoke as a vapour
injected directly into the gas chromatograph and the other tests
involved condensing the smoke in a liquid and the subsequent analysis
of the resulting solution.
Direct injection of the vapour was done with a 2ml. gas tight
syringe. Samples of the smoke were taken into the syringe from the
exhaust tube of the gas generator and introduced directly into the
gas chromatograph. The analytical conditions were as given in Table
1. The resulting chromatogram showed two peaks, one of which coincided
with water and a second later peak. However, the retention time
was different from that of injections of liquid propylene Glycol
and the peak was broader. When a reference injection of standard
propylene glycol vapour was made the peak coincided with that of
the smoke sample. Peak broadening is an effect often associated
with the injection of relatively large volumes of gas and the phenomenon
may result in the combination of two peaks into an apparently single
peak. Thus although vapour injection was an attractively simple
method of determining the concentration of propylene glycol in the
smoke it was first necessary to establish that its use did not mask
the presence of other compounds. Hence the need to examine condensed
samples of smoke.
Smoke was condensed by trapping in water. The water was contained
in a Dreschel bottle connected to a Factory Inspectorate Mark 1
portable pump. Smoke was drawn from the generator and bubbled through
the water at a rate of 500ml. min. -1. Sampling was carried on for
15 minutes after which time the resulting solution was analysed.
The analytical conditions were the same as previously. 10ml injection
of the solution were made into the gas chromatograph. The only peaks
apparent were those resulting from water and propylene glycol. This
result suggested that propylene glycol was the only organic compound
present and that no decomposition had occurred. Further confirmation
was achieved by using a temperature programming technique. The gas
chromatograph oven temperature was slowly increased in a controlled
way instead of the normal isothermal operation. Temperature programming
allows the separation of peaks which are combined together under
isothermal conditions. A programme from 60 to 2000C at 40C min -1.
was used but once again the only peaks produced were the water peak
and the major peak coinciding with propylene glycol. At this stage
it was assumed that propylene glycol was the only compound of significance,
and so the vapour injection technique could be used for the quantitative
analysis of smoke atmospheres. The peak broadening would not be
masking other substances.
2. Quantitative Analysis of the Atmospheres Produced
The primary objective of the tests was to measure the concentration
of propylene glycol present in the smoke and to express this as
a function of reduced visibility and light intensity. The tests
were carried out using a glass chamber 40cm x 30cm x 30cm. Light
from a source was passed through the chamber and detected by a photocell
positioned on the opposite wall of the chamber. The light path used
was thus 30cm. The reduction in photocell signal was used as a measure
of the degree of obscuration produced when smoke from the generator
was passed into the chamber.
Simultaneously a sample of the atmosphere was withdrawn from the
chamber using a 2ml. gas--tight syringe and introduced into the
gas chromatograph for analysis. The standard analytical conditions
Initially a single atmosphere was generated and repeated samples
taken and analysed in order to obtain information on homogeneity
of the atmosphere. Subsequently further atmospheres were generated
and vapour samples taken for analysis. The results obtained are
presented in Table 2.
2.2. Le Maitre Fluid B
2.2.1. Analysis of the Fluid
The objective was once again to confirm the supposed composition
of the fluid. This was carried out in similar fashion to Le Maitre
Fluid A. Samples of glycerine were injected into a gas chromatograph
operating under the conditions listed in Table 3. Subsequent injection
of the fluid showed glycerine to be the only organic component.
It should be noted that the peaks produced were of poor shape since
glycerine is a substance not readily amenable to chromatographic
2.2.2. Analysis of the Smoke Generated
As for Le Maitre
fluid a two series of tests were carried out. Firstly the smoke
generated was condensed in water by pumping through a Dreschel bottle
containing the absorbing solution. Samples of the condensate were
subsequently analysed and shown to give a similar chromatogram to
that of the virgin fluid. There was no indication of decomposition
having taken place.
Attempts were then made to inject the vapour directly into the
gas chromatograph. This was not successful since the already broad
peaks were so distorted by the injection of the large volume of
vapour as to make them useless. After various unsuccessful attempts
at devising a more suitable system it was decided simply to use
the detector with no attempt at separation. A tube containing only
glass yarn was used to connect the injector to the detector. Even
using this system there was a degree of peak broadening for the
vapours injected but it was useable.
Testing of the opacity of the generated atmosphere also produced
additional problems with condensation of the glycerine on the walls
of the test chamber. To overcome this the light source and photomultiplier
were positioned inside the chamber. This overcame the condensation
problems to a large extent. The result obtained are shown in Table
3.1. Analysis of Smoke Atmospheres
The results show that there was no measurable decomposition of
either propylene glycol or glycerine during the smoke generation
process and so only these compounds need to be considered for the
toxicology studies. There may have been some slight decomposition
but at a level insufficient to be shown by the techniques used here.
Such decomposition if it occurs at all, is unlikely to be significant.
Quantitative analysis of the generated atmospheres shows a potentially
wide range of concentration. It was found that plots of light transmission
against concentration for the two atmospheres were similar and the
following discussion applies to both materials. Attempts were made,
with some success, to relate light transmission and light absorbance
with vapour concentration. In this respect, if absorption of the
radiation by the chemical species was the only mechanism operating
Beers Law would be expected to apply. This draws a linear relationship
between absorbance and concentration given a constant pathlength.
Such a linear relationship is also expected for attenuation of light
by scattering by dilute aerosols. however, as can be seen in Figure
1, this relationship does not apply well here. There is clearly
a curved function indicating that the attenuation of the light in
this case is not well described by simple theory. Since we are dealing
here with scattering by a concentrated (and probably polydisperse)
aerosol, in which multiple scattering events are significant, such
a non-linear relationship between vapour concentration and absorbance
is not an unexpected result.
A further complication is the heterogeneous nature of the generated
atmospheres. Duplicate samples of the atmospheres through the vessel
showed a range of vapour concentration indicating the rather variable
nature of the atmospheres produced. On occasions this phenomenon
was clearly visible as clouds of vapour moved through the chamber.
In this respect Le Maitre B seemed to produce a much more consistent
and stable smoke. Atmospheres of this character are typical of real
circumstances and so are not a disadvantage of the smoke generator.
It does, however, tend to make the correlation of vapour concentration
with light reduction more difficult. As a result there is inevitably
a loose relationship between absorbance and vapour concentration
and in the circumstances the results in Figure 1 are satisfactory.
They show that there is an empirically determined relationship and
serve as a guide to the vapour concentration which can be generated
and used. Highest concentrations measured where 1150 mg.m-3 although
there is little doubt that concentrations well above this could
be generated. in this case the light intensity would have been so
reduced that no meaningful measurements could have been made. It
is estimated that the highest concentration capable of generation
is of the order 1500 mg.m-3. depending on circumstances.
In practical application of the smoke generator, light transmissions
over distances greater than our 'test' distance of 30cm are likely
to be of interest. Accordingly we have estimated, from our data,
approximate light transmissions for concentration of 100, 200, 500
and 1000 mg/m3. of vapour at distances (in each case) of 1,2, and
5m. These datas are presented in Table 5. The table shows, for example,
that a vapour concentration of 200 mg/m3. possesses a light transmittance
of about 3% for a 2 meter path. These data should be taken as approximate
values only, and not necessarily as measures of 'visibility', since
the latter concept involves, in practical situations, questions
of colour and contrast between an object and its surroundings.
3.2. Safety of the Smoke Generated
A MAJOR CONSIDERATION
IN SMOKE GENERATION IS THE SAFETY OF INDIVIDUALS EXPOSED TO THE
SMOKE. Many substances have been shown to be harmful to individual
health either in the short or the long term. Clearly it would be
inadvisable to generate atmospheres containing potentially hazardous
substances. The work described above has shown that only a single
substance other than water is present in the smoke produced.
The recognised limits of industrial exposure to chemicals in the
work place are the threshold limit values (T.L.V.). There are of
i) The time weighted average T.L.V. (T.W.A.T.L.V.) which refers
to a maximum average concentration to which an individual may be
exposed throughout a working lifetime. It assumes an exposure time
of up to 40 hrs/week for many years.
ii) A short term exposure limit (S.T.E.L.) which is a concentration
greater than the (T.W.A.T.L.V.) to which an individual may be exposed
for periods not exceeding 15 minutes.
iii) A ceiling concentration which may never be exceeded.
It must be stressed that the T.L.V. concept relates to industrial
exposure and so is selective in those of the population to whom
it applies. There are not T.L.V. data for every conceivable substance,
and neither propylene glycol or glycerine are listed. The lack of
data cannot be taken to mean that a substance is either completely
harmless or highly dangerous, rather that it has not presented a
particular industrial problem. In this case it is presumably because
under normal conditions they are relatively involatile and so unlikely
to accumulate in significant concentrations. In the absence of T.L.V.
it is necessary to consider what other information is available.
3.3. Toxicology of Propylene Glycol & Glycerine
Propylene glycol is an allowable constituent of foodstuffs and
pharmaceutical products. it is contained, for example, in soft drinks
and suntan lotions. Although neither of these are inhaled there
is no reason why this route should pose an additional hazard. Experiments
on rats and monkeys have shown that exposure to saturated atmospheres
for up to eighteen months produces no ill effects. Equally no effects
have been noted in man as a result of inhalation.
Glycerine is also allowed in foodstuffs and pharmaceuticals and
is very widely used. It is also used as a bacteriostat. No toxicity
effects on animals or man have been noted even at concentration
well in excess of those relevant here.
THUS NEITHER OF THE SUBSTANCES USED IN THE SMOKE GENERATORS HAS
BEEN SHOWN TO HAVE ANY ADVERSE EFFECTS IN MAN.
In general, it is prudent to avoid undue exposure to any substance
but there is no reason to suppose that any harmful effect will result
even from continued exposure to the smoke generated. In typical
use where the exposure is restricted and limited there is every
reason to consider the devices safe.
1) The composition of the fluids were as stated by the manufacturer.
2) There was no evidence that during smoke generation either propylene
glycol or glycerine degraded to form other compound.
3) The generators are capable of producing concentration in excess
of 1500 mg.m-3 which would result in visibility being reduced to
less than 1 metre. At increasing concentration in excess of the
saturation level precipitation may become a problem.
4) No threshold limit values exist for limiting industrial exposure
to either propylene glycol or glycerine. Other toxicological data
show that these compounds present no known hazard to health.
1. Handbook of environmental data on organic chemicals, K. Verschueren,
|Table 1: Analytical Conditions for
Gas Chromatographic Analysis of Propylene Glycol
2 Metre x 1/4in. outer diameter glass
10% Carbonwax 20M
150 Degrees C
250 Degrees C
250 Degrees C
Nitrogen at a flowrate of 30ml/min
|Table 2: Light Penetration of Propylene Glycol
*Measured for 30cm path
|Table 3: Analytical Conditions for
Gas Chromatographic Analysis of Gylcerine
2 Metre x 1/4in. outer diameter glass
100 to 200 Degrees C at 4 Degrees min -1
250 Degrees C
250 Degrees C
Nitrogen at a flowrate of 30ml/min
|Table 4: Light Penetration of Gylcerine Atmospheres
*Measured for 30cm path
|Table 5: Calculated Light Transmittance for Concentrations of Vapor
of Vapor (mg/m3)
|Light Transmittance, % for Distance Indicated
2 x 10-2