Cold Water Diving – Precautions (Paul Clunas)
Pressure 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 cylinder.
At very low temperatures a regulator can free flow when it’s used in cold and especially fresh water. This phenomenon occurs when ice crystals form in the demand valve and prevent the valve from closing after you’ve taken a breath. The demand valve fails in a progressive manner, beginning with a small bubble of air escaping from the valve as you pause between breaths. This is the first sign of a serious problem and you should immediately make your way to the surface.
If ignored, the situation will worsen until the valve is fully open and free flowing violently. Free flows are relatively easy to avoid by making sure that your regulator is approved for CE Coldwater use, avoiding regulators marked > 10°C and by following a few simple precautions. It also pays to make sure that the regulator is recently serviced and in excellent working order.
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 free flow, get your buddy to close and reopen the valve.
Check the equipment is suitable
Regulators sold in the UK as suitable for use in northern European waters should comply with EN250. However, some regulators on sale in the UK are NOT suitable for use in waters colder than 10°C. These regulators should be clearly marked on the body of the 1st stage with >10°C and you should check the regulators you are using for any such marks and not use them below their design temperature.
Defensive diving
Even with a properly designed and manufactured cold water regulator, free flows can still occur but taking suitable precautions should minimise the risk:
- Ensure that your cylinder is filled with air as dry as possible.
- Keep your cylinder out of the cold. (Don’t leave it in your car overnight.)
- If possible do not jump into the water but enter via ladder / steps / slipway.
- The 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.
- Don’t breath from the regulator in air. Ensure both stages are submerged before taking shallow breaths to test.
- Inflate BCDs and wings slowly – preferably during the exhalation phase to ‘unload’ the 1st stage.
- If you have a 2nd stage with a breathing resistance adjustment, remember to always have the adjuster set to minimum when it is not being breathed from.
- Avoid fast air flows caused by breathing heavily, using the purge button or filling DSMBs.
- Restrict yourself to no-stop diving and depths from which you can make a safe ascent.
Safe Diving!
