Dräger TR 60 tauchretter

One of the first nitrox tauchretters build in the 60’s

Recently I was able to buy a Dräger Tauchretter Model TR 60. This life saving dive jacket was designed in the 60’s and is a surprising rebreather. One of the most interesting aspects of this rebreather is that in fact it is a semiclosed rebreather! It is well known that using pure oxygen rebreathers to escape from depth introduces a big risk of oxygen toxicity. Semiclosed rebreathers offer a improvement because the breathed gas has a much lower oxygen content. This rebreather uses EAN 50!

To understand how the rebreather works on depth I here made two calculations to show why the partial pressure of oxygen is much lower with a semiclosed rebreather compared tot the standard oxygen rebreathers. The working principle is based on the semi-closed equation:

The unit is equipped with a constant mass flow regulator with a gas flow of 3,0 l/min. This flow is constant to a depth of 40 meter. This means that the intermediate pressure is 10 bar on the orifice. The flow will continue to 10 bar and the stops. This will happen o a depth of 90 meters. Becauese the flow is constant to half the IP at 40 meter there will be exact 3,0 ltr/min. Imagine a diver who uses 0,5 ltr oxygen per minute the partial pressure he is breathing can be calculated with the mentioned equation.

FiO2 = unknown

Qs = 3,0 ltr/min

FsO2 = 0,5 (EAN 50)

VO2 = 0,5 ltr/min

FiO2 = ((3,0ltr/min x 0,5)-0,5)) / (3,0 ltr/min – 0,5 ltr/min) = 0,4 meaning the fraction of the inhaled gas is 0,4. The gas is EAN 40 breathed at 40 meter the partial pressure of oxygen at depth is 5 bar ambient pressure x 0,4 bar oxygen pressure = 2 bar ! In the 60’s military divers where supposed to be capable of breathing 2 bar oxygen! Fortunately this has been changed, although this unit would only be used in a emergency situation and therefore the 2,0 bar is not so crazy..

When the diver uses more oxygen due to swimming or stress the unit can be used deeper. Imagine a oxygen consumption of 0,8 liter per minute the inspired gas is:

iO2 = ((3,0ltr/min x 0,5)-0,8)) / (3,0 ltr/min – 0,8 ltr/min) = 0,318. When a gas is breathed with a fraction of 0,318 th maximum depth when 2 bar oxygen pressure is allowed is 2bar / 0,318 = 6,28 bar. On a depth of 52,8 meter the rebreather feeds EAN 31,8 resulting in a oxygen pressure of 2bar.

In the following manual  you find more details about this very nice unit!

I would like to thank Joe Brandt for his kind cooperation sending me the manual and info about this great unit.
Please check Joe’s website here