Note: Descriptions are shown in the official language in which they were submitted.
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Gas mixture for testing the functioning of smoke detectors
Description
The invention relates to a gas mixture for testing the
functioning of smoke detectors, consisting of a propellant gas
and at least one aerosol component that is admixed to said
propellant gas with a mixing ratio of no greater than 2
percent by weight and consists at least of one of the
materials sebacic acid-bis-2-ethyl-hexylester, sebacic acid-
diester containing diverse ester groups, paraffin oil, dibutyl
phthalate, phthalic acid-bis-2-ethyl-hexylester and
butyloxyethanol.
Smoke detectors are used to detect smoke particles or aerosols
which can arise during a fire. Commercially-available smoke
detectors include both ionization smoke detectors and
especially scattered-light smoke detectors which measure the
light scattered on smoke particles or aerosols in an optical
measuring chamber.
Smoke detectors and smoke detector systems mostly have an
operating life of several years and require periodic function
checking to insure that they operate without any problems,
said checking generally being undertaken by a test gas which
simulates an aerosol being applied to the measurement chamber.
Thus for example propellant gases with a high molecular weight
have been used which were capable of simulating an aerosol
without additional substances. A propellant gas mixture with a
suitable boiling point of the components, between -20 C and
+10 C, has shown itself to be very effective and applicable
for all detector types. The most widely used propellant gases
were the chloroflurocarbons, which also fulfilled the
conditions of non-inflammability and non-toxicity. One of
these gas mixtures is described in CH-A-501 284.
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According to the Treaty of Montreal concluded in September
1987, the use of chloroflurocarbons has been banned from 1995
onwards in all countries because of their damaging effect on
the ozone layer, and thus the above-mentioned propellant gases
can no longer be used.
EP-A-0443 912 describes a gas mixture which does not damage
the ozone layer and which contains a proportion of dimethyl
ether and a proportion of 1,1,1,2-tetrafluoroethane. Although
this mixture produces good results when used in refrigerating
devices and as a propellant gas, it is however not very well
suited to specific use as a test gas for smoke detectors since
it does not contain any aerosols. And this characteristic
leads to condensation being able to be formed by the cooling
down of the air and thereby an alarm possibly being able to be
triggered.
EP-B-0 663 432 describes a gas mixture of the type given
above, which consists of 80 to 60 percent by weight of
1,1,1,2-tetrafluoroethane and 20 to 40 percent by weight of a
pressure-reducing gas, which consists of at least one of the
materials n-butane, iso-butane, a mixture of propane/n-butane,
a mixture of propane/iso-butane, dimethyl ether (CH3-O-CH3),
methylal (CH3-0-CH2-CH3) and ethylene methyl ether (CH3-0-CH-
CHZ). This gas mixture contains an admixed aerosol-forming
component which consists of at least one of the materials
sebacic acid-bis-2-ethyl-hexylester, sebacic acid-diester
containing diverse ester groups, paraffin oil, dibutyl
phthalate, phthalic acid-bis-2-ethyl-hexylester
butyloxyethanol, triethylenglycol and triethylenglycol-diester
and is admixed to the gas mixture in a ratio of maximum 2
percent by weight.
The gas mixture described in the said EP-B has been very well
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proven over many years for testing the functions of smoke
detectors, but contains a fluorinous substance, which was
banned in Denmark a short time ago and will presumably also be
banned in other countries.
The invention is now intended to create a gas mixture for
testing the functioning of smoke detectors, which, with the
same good characteristics as the gas mixture described in EP-
B-0 663 432, does not contain any fluorinous substance.
In accordance with the invention this object is achieved by
the propellant gas consisting of iso-butane or n-butane or
propane or any given mixtures thereof
As well as the new requirement to dispense with fluorinous
substances, the requirements have previously existed for gas
mixtures used for testing the functions of smoke detectors for
the gas mixture to be a liquid between -10 C and +50 C and be
incombustible, and for it to have vapor overpressure of <- 11
bar at +50 C (specification for spray cans). Since in
principle no gas mixture exists which fulfills all these
requirements, the invention forgoes the incombustibility of
the gas mixture.
The inventive gas mixture is thus combustible like any paint
or deodorant spray and, compared to previously known mixtures
for testing the functions of smoke detectors, has a better
shelf life, lower manufacturing costs and a smaller average
molecular weight. The latter means that it diffuses more
quickly into the detector on application and diffuses more
quickly from the detector on evacuation.
Preferred and advantageous embodiments of the inventive gas
mixture are claimed in the dependent claims.
The inventive gas mixture for testing the functioning of smoke
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detectors is described in greater detail below with reference
to exemplary embodiments, with the gas mixture being referred
to as the "test gas".
The important condition for the test gas is the preservation
of the ozone layer. Using this as the starting point, only
chlorine-free gases are considered as propellant gases, since
chlorine is known to break down the ozone layer. The test gas
may also not contain any chlorofluorocarbons, since fluorinous
substances are banned at least in Denmark. For these reasons
the propellant gas of the test gas consists of iso-butane or
n-butane or propane or any given mixtures thereof, preferably
of a 1.1 0.2/0.9 0.2 mixture (mol/mol) of iso-butane and
propane or of a 1.0 0.2/1.0 0.2 mixture (mol/mol) of n-butane
and propane.
The at least one aerosol component of the test gas contains at
least one of the following materials:
= Sebacic acid-bis-2-ethyl-hexylester
= Sebacic acid-diester containing diverse ester groups
= Paraffin oil
= Dibutyl phthalate
= Phthalic acid-bis-2-ethyl-hexylester
= Butyloxyethanol
with the total proportion of all aerosol components amounting
to <- 2 percent by weight. Generally the proportion of the
aerosol components ~ is 0.5 percent by weight, in a preferred
embodiment of the test gas it lies between 0.001 percent by
weight and 0.3 percent by weight.
The test gas is put into a pressurized container of the normal
test gas canister type which is used in a REG type detector
test device made by Siemens Schweiz AG, Building Technologies
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Group (formerly Cerberus AG). For the test process the
detector tester is pushed over the detector. By pressing the
detector tester onto the detector the test gas is sprayed onto
the detector, flows into its measuring chamber and thus
simulates the presence of fire aerosols.
Practical trials involving checking the functions of
ionization smoke detectors and of optical smoke detectors with
the inventive test gas have led to the following results:
= The new propellant gas with the same spray time but
with a smaller concentration of the at least one
aerosol component, produces a relatively long-lived
aerosol and larger scatter signals are measured than
with known test gases.
= Because it has a lower molecular weight, the aerosol
penetrates rapidly into the measuring chamber of the
detector and diffuses rapidly from it once testing is
at an end.
= For a similar concentration of the aerosol components,
iso-butane produces a less long-lived aerosol than
propane.
