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RESPIRATORY PROTECTION

The self-rescuer is thus such that it affordsthe user a great deal of mobility along theescape route. This is particularly beneficialwhen the person concerned has to crawl.Wearing the apparatus over the head – aconcept proven a million times over with filter self-rescuers – makes for minimum restriction of head movement. The headharness can be adjusted and thus adaptedon a case to case basis. These featureswere defined from the South-African miningauthorities in 1985 for the safety of theSouth-African miners.

Breathing cycleThe oxygen required for breathing is supplied by a solid chemical substance,potassium dioxide (KO2). After entering the KO2-cartridge, the exhaled air – containingwater vapour (H2O) and carbon dioxide(CO2) – initiates a reaction in which thechemically-bound oxygen (O2) is releasedand the CO2 is absorbed in the KO2. Alternating between inhalation and exhala-tion, the breathing air flows from thebreathing bag through the KO2-cartridge to the heat exchanger and back again. On account of the generated heat, whichwarms the breathing air, the Oxyboks isthus provided with a simple, but reliableheat exchanger. When the user inhales, thewarm air flows trough the heat exchangerand is cooled on its internal cooling sur-faces 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 sur-faces in the opposite direction at a tem-perature of 37 °C. The air absorbs the heatand 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. Duringinhalation, this volume flows again throughthe KO2. Such to and fro respiration em-ployed by the KO2 cartridge, through whichthe breathing air flows twice on this occa-sion, leads to an extremely high degree ofpurification of the used air.As the chemical reaction of the KO2 pro-duces somewhat more oxygen than it con-sumes, a relief valve is required. This valveallows surplus oxygen to flow off, but pre-vents ambient air from entering the circuit.

The Oxyboks features a starter cartridgewhich supplies oxygen via the mouthpieceimmediately and independently of the initial breathing phase. This is specially important in situations where every secondis important.

Features of the new SABS Standard In 2001 the new standard SABS 1737:2001for “Body worn escape type breathing apparatus” was published in South Africa.The requirements on oxygen self-rescuersare drastically increased with this new stan-dard. First, the ventilation rate has been increased to 35 l/min as well as the CO2-content of inhaled air to 4,5 % volume.

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Dräger Oxyboks K 35 Now approved in accordance to South AfricanBureau of Standards

HistoryThe Dräger Oxyboks series is intended forself-rescue when working underground andstands for a maximum of safety in extremesituations. Since 1986 Dräger sold up to100.000 of these reliable units.

In developing this oxygen self-rescuer,Dräger Safety gave consideration to thehigh requirements of the South Africanmining industry with respect to lightweightdesign, ergonomic carrying and handling,ease of donning the rescue pack, rugged-ness, reliability, inhalation temperature,

breathing resistance and length of time for which protection is required. The factthat the Oxyboks, in an emergency, is wornwith a comfortable head harness meansthat miners can move freely even when narrow and low openings make uprightstanding impossible. For the use in an emergency the OxyboksK series is worn directly over the head. Thismethod of carrying was made possible bymeans of consistent weight optimisation.

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On the other hand, the sequence for thedurability test of the unit was tightened andamplified 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 environ-ment 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 35As the result of permanent product ad-vancement (since 1986), Dräger Safety further improved the self contained self-rescuer “Oxyboks K”. With the approval acc. to SABS 1737:2001the Oxyboks K 35, is now the second avail-able unit complying with this standard.The SIMRAC1, which conducts annual com-parisons of oxygen self-rescuers, samplesone percent of SCSR units from mines ontheir service capability. The Oxyboks K has proved itself as an outstanding unit; the specified duration of 30 minutes hasbeen met with only marginal deviations; the Oxyboks K had the fewest internal defectsand the fewest failed units during the test.The emphasis on the further developmentof the Oxyboks K 35 were, according to thechanged approval requirements, an improv-ed CO2-recipe, that at a higher breathingrate 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

1 Safety In Mines Research Advisory Committee

a longer duration of almost 10 minutes. To be able to fulfil the increased mechan-ical requirements, the damping of the Oxyboks K 35 was improved on differentareas. For example, the KO2-compound is placeddifferently in the chemical cartridge, whichleads to an improved shock resistance ofthe cartridge. Furthermore, the oxygen selfrescuer is equipped in the case with addi-tional damping elements. These reduce thestress on the unit especially from the high-frequency sinusoidal vibrations.The majority of the before mentioned im-provements are not observable for the user.

Visible is however the bump protectoraround the plastic case, which considerablyreduces the higher impact during the test.As underground rescue is one of DrägerSafety’s core competencies, the new Oxyboks K 35 stands for outstanding performance and reliability in case of an emergency.

Kirstin von WaadenVolker BiermannDräger Safety AG & Co. KGaA kirstin.vonwaaden@draeger.comvolker.biermann@draeger.com

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