Chill out in safety...
EU norm considers cold water diving to be when the temperature of the
water is equal to or drops below 6 degrees C. Whilst the lake waters at
Vobster Quay stay reasonably warm for most of the year, the water
temperature can drop sharply during the winter months. Even during the
summer months, deeper parts of the lake can still be relatively cold.
perform differently in cold water diving compared to temperate water -
the aim is to do everything that you can to prevent the regulator
freezing which, in turn, causes the dreaded free flow effect. By
following simple guidelines, the risk of free flows can be minimised
variations in gases generate temperature variations - as most divers
are aware, gases heat up during compression (filling a cylinder
rapidly) and cool down during expansion (emptying a cylinder rapidly).
This has an effect on the regulator 1st stage - the higher the pressure
in the cylinder, the more effect it has. The cooling down effect of the
1st stage will be increased when the regulator is working on a 300-bar
To mimimise the risk of free flows next time you dive in cold water, we offer the following advice...
- To limit freezing risks, a lower pressure tank is recommended for cold water. The higher the pressure, the higher the risk!
regulators designed specifically for cold water diving! These
regulators are often either environmentally sealed or use a special
'heat sink' that uses the cold water to 'warm' the 1st stage which
limits the formation of ice. Look for regulators that meet the EN250 standard for cold water performance.
breathing from the 2nd stage out of the water when the air temperature
is low. The aim is to minimise the cooling effect of the air and the
diver's breath by not 'overworking' the 1st stage. Practising air
sharing and deploying surface marker buoys in cold water is not ideal!
air fills from a reputable source - the drier the compressed air, the
lower the freezing risk! Vobster's air is checked regularly for purity
and is very dry!
cool 1st stage can be warmed by the surrounding water - remember that
the air will generally always be colder than the water, even during the
winter months. Maximise the warming effect of the water.
greater the amount of exposed metal, the greater the warming effect of
the water can be maximised - pull back hose protectors on metal hose
ends. This also helps to extend the life of your hoses as it stops
debris and water trapped against metal fittings from causing corrosion.
- Inflate BCDs and wings slowly - preferably during the exhalation phase to 'unload' the 1st stage.
you have a 2nd stage with a breathing resistance adjustment, remember
to always have the adjuster set to minimum when it is not being
further advice on cold water diving specific to the equipment you use,
consult with a qualified service technician or the equipment
It's important to understand why free flows occur and how to handle
them should they ever occur. Regulator 2nd stages essentially act as
pressure relief valves - they are designed to do this. Normally in
temperate diving, if an adjustable 2nd stage purge button hits the
water or is even lightly touched when it is set to maximum but not
being breathed from, it can go into free flow.
To stop this sort of free flow, put a thumb or finger over the 2nd
stage mouthpiece to break the flow of air and then - if the 2nd stage
offers such a facility - set the breathing resistance level to minimum.
If this doesn't stop the freeflow, get your buddy to close and reopen
the valve. ||
Regulators - when set up correctly as per manufacturer's procedures -
are design to easily give the diver air to breathe. A 1st stage freeze
will cause the mechanism to free open within the 1st stage which will
cause a 2nd stage free flow (remember it's a pressure relief valve!).
Follow your training and ABORT THE DIVE
If the cause of the freeflow is thought to be a 1st stage problem, the
regulator will still not work properly even on dry land and in a warm
environment. Also, try to identify where the free flow came from - was
it a 2nd stage or your Autoair or BCD/wing inflator?