|
|
|
|
|
|
|
|
|
|
|
|
History
The Dräger Oxyboks series is intended for
self-rescue when working underground and
stands for a maximum of safety in extreme
situations. Since 1986 Dräger sold up to
100.000 of these reliable units.
In developing this oxygen self-rescuer,
Dräger Safety gave consideration to the
high requirements of the South African
mining industry with respect to lightweight
design, ergonomic carrying and handling,
ease of donning the rescue pack, ruggedness,
reliability, inhalation temperature, breathing resistance and length of time
for which protection is required. The fact
that the Oxyboks, in an emergency, is worn
with a comfortable head harness means
that miners can move freely even when
narrow and low openings make upright
standing impossible.
For the use in an emergency the Oxyboks
K series is worn directly over the head. This
method of carrying was made possible by
means of consistent weight optimisation.
The self-rescuer is thus such that it affords
the user a great deal of mobility along the
escape route. This is particularly beneficial
when the person concerned has to crawl.
Wearing the apparatus over the head – a
concept proven a million times over with
filter self-rescuers – makes for minimum
restriction of head movement. The head
harness can be adjusted and thus adapted
on a case to case basis. These features
were defined from the South-African mining
authorities in 1985 for the safety of the
South-African miners.
Breathing cycle
The oxygen required for breathing is
supplied by a solid chemical substance,
potassium dioxide (KO2). After entering the
KO2-cartridge, the exhaled air – containing
water vapour (H2O) and carbon dioxide
(CO2) – initiates a reaction in which the
chemically-bound oxygen (O2) is released
and the CO2 is absorbed in the KO2.
Alternating between inhalation and exhalation,
the breathing air flows from the
breathing bag through the KO2-cartridge
to the heat exchanger and back again.
On account of the generated heat, which
warms the breathing air, the Oxyboks is
thus provided with a simple, but reliable
heat exchanger. When the user inhales, the
warm air flows trough the heat exchanger
and is cooled on its internal cooling surfaces
to such an extend that it can be
inhaled again without problem. The heat
exchanger is re-cooled by the exhaled air
which flows around the same cooling surfaces
in the opposite direction at a temperature
of 37 °C. The air absorbs the heat
and conveys it back into the KO2 cartridge.
The breathing bag downstream of the
cartridge assumes all the exhaled air after
it has passed once in its entirety the KO2-
cartridge in the outward direction. During
inhalation, this volume flows again through
the KO2. Such to and fro respiration employed
by the KO2 cartridge, through which
the breathing air flows twice on this occasion,
leads to an extremely high degree of
purification of the used air.
As the chemical reaction of the KO2 produces
somewhat more oxygen than it consumes,
a relief valve is required. This valve
allows surplus oxygen to flow off, but prevents
ambient air from entering the circuit.
The Oxyboks features a starter cartridge
which supplies oxygen via the mouthpiece
immediately and independently of the
initial breathing phase. This is specially
important in situations where every second
is important.
Features of the new SABS Standard
In 2001 the new standard SABS 1737:2001
for “Body worn escape type breathing
apparatus” was published in South Africa.
The requirements on oxygen self-rescuers
are drastically increased with this new standard.
First, the ventilation rate has been
increased to 35 l/min as well as the CO2-
content of inhaled air to 4,5 % volume.
On the other hand, the sequence for the
durability test of the unit was tightened and
amplified by additional testing.
- The climatisation of the units at the start
of the test sequence has been tightened.
The time of storage in a warm environment
at 70°C was doubled to 144 hours
compared to the old test.
- The impact test of the units has been
more difficult by increasing the dropping
height from 1 to 1,5 metres. The units
are dropped seven times on their
six main axis.
- Additionally, the units are stressed in
their main axis for a duration of 9 hours
with sinusoidal, low-frequency vibrations
(10 – 450 Hz).
- The entire unit is stressed as well for
a duration of 9 hours with sinusoidal,
low-frequency vibrations (30 – 35 Hz).
- Furthermore, 3000 bumps with an
acceleration of 100 m/s2 are applied
to the unit
- Two additional leak tests in 45°C warm
water verify the tightness of the unit
- The number of tested units was more
than doubled. Defective units are not
acceptable.
- Six additional tests remain unmodified
component of the test sequence
Main Advantages of Oxyboks K 35
As the result of permanent product advancement
(since 1986), Dräger Safety
further improved the self contained selfrescuer
“Oxyboks K”.
With the approval acc. to SABS 1737:2001
the Oxyboks K 35, is now the second available
unit complying with this standard.
The SIMRAC1, which conducts annual comparisons
of oxygen self-rescuers, samples
one percent of SCSR units from mines on
their service capability. The Oxyboks K
has proved itself as an outstanding unit;
the specified duration of 30 minutes has
been met with only marginal deviations; the
Oxyboks K had the fewest internal defects
and the fewest failed units during the test.
The emphasis on the further development
of the Oxyboks K 35 were, according to the
changed approval requirements, an improved
CO2-recipe, that at a higher breathing
rate per minute is able to link more CO2.
This leads thereto that the Oxyboks K 35,
at similar breathing conditions (30 L/min;
4 volume %) as the Oxyboks K, has yielded
a longer duration of almost 10 minutes.
To be able to fulfil the increased mechanical
requirements, the damping of the
Oxyboks K 35 was improved on different
areas.
For example, the KO2-compound is placed
differently in the chemical cartridge, which
leads to an improved shock resistance of
the cartridge. Furthermore, the oxygen self
rescuer is equipped in the case with additional
damping elements. These reduce the
stress on the unit especially from the highfrequency
sinusoidal vibrations.
The majority of the before mentioned improvements
are not observable for the user.
Visible is however the bump protector
around the plastic case, which considerably
reduces the higher impact during the test.
As underground rescue is one of Dräger
Safety’s core competencies, the new
Oxyboks K 35 stands for outstanding
performance and reliability in case of an
emergency.
Kirstin von Waaden
Volker Biermann
Dräger Safety AG & Co. KGaA
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
Dräger Safety AG & Co. KGaA |
|
|
Revalstrasse 1 |
|
|
23560 Luebeck, Germany |
|
|
|
Tel +49 451 882 0
Fax +49 451 882 2080
|
|
|
|
