The gas in the breathing circuit:With the dosage selector set in the RED position (0.3 dosage) and gas supply with RED gas containing 40 % Oxygen the breathing gas in the circuit will have a minimum value of 28 % Oxygen steady state.

Equivalent Air diving depth (EAD):A minimum value of 28 % Oxygen gives a maximum value of 72 % Nitrogen, which is the basis for the calculation of the equivalent air diving depth (EAD).

Oxygen exposure:For normally functioning apparatus, the partial pressure of Oxygen varies between:

O2ppO2 surfaceppO2 at 40 m

40%0.402.0

28%0.281.4

As the IS Mix apparatus is of the constant oxygen fraction model (FO2 ), a high ppO2 value is only reached at the maximum diving depth and therefore provides a safety margin in relation to EN 14143 which allows for a short term partial pressure of up to ppO2 = 2.0 bar.

Maximum permitted diving depth for RED gas (MOD RED 40% - NATO C-mixture): The maximum permitted diving depth is determined by the maximum permitted ppO2.

If MOD is calculated at the lowest steady-state fraction of 28 % and maximum ppO2 is set to 2.0, this gives a maximum diving depth of 61.4 m.

If MOD is calculated at the highest fraction of 40 % (pure by-pass gas) and maximum ppO2 is set to 2.0, this gives a maximum diving depth of 40 m.

This short term high ppO2 only occurs with pure gas throughout the breathing circuit. This happens, for example, following a period of prolonged and vigorous by-pass operation at the maximum depth, which does not occur in normal use. A by-pass that is used vigorously only occurs in an emergency which also stipulates that the dive must be aborted and the ascent must begin which immediately reduces ppO2 through the decreasing pressure.

Descent:Following a dive at a normal rate of descent from the surface, the gas in the breathing circuit will never achieve the maximum value recommended in EN 14143 of ppO2 for short-term exposure.