Equipment & Procedural ModificationsWhen is it too cold to dive?
I have dove in the Artic in February when the water temperature was 100 o F warmer then the air. The salt water temperature was 31 o F and the air was –70 o F without wind chill factored in. I would much rather be the diver then the tender in this situation.As long as you can get down to the liquid and keep it open you can dive it.
The real question is, when is it too cold to tend?
Water temperatures rarely get below 30 o F and there is never any wind chill.
I have spent several hours below the ice in a dry suit and was warmer then the top-side crew on the surface. Problems to be overcome:
-2nd stage diaphragm freeze up before submersion (froze open or closed)
- exhaust valve freeze up before submersion (froze open or closed)
- ice in umbilical gas hose causing lose of surface supply
- ice in pneumo causing loss of depth monitoring
- start up of equipment
- protection of surface crew from wind and cold
- getting and maintaining access to water
- moving ice
- getting to dive site
- gas build up causing loss of ice bearing strength
- predive planning and job hazard analysis (J.H.A.)
- emergency contingency plan (E.C.P.)
- filter packs, regulators and racks freezing
- power tools freezing
- battery life of electrical equipment reduced
- in water decompression hazards
- loss of hot water for hot water suits2nd stage diaphragm freeze up before submersion (froze open or closed)
The formula PV = nRT shows that:
- Reduce the pressure and temp. will reduce
- Reduce the Volume (diameter) and temp. will reduce
Regulators produce cold, they reduce pressure and volume.
When moisture in the second stage is exposed to the frozen housing the diaphragm will often seals closed. This is most common before entering the water and I have never herd of this happening underwater. Go to free flow and wait on the ladder with the helmet submerged until the demand is working properly. Avoid using the purge button because this can tare the diaphragm.
- remove and dry the diaphragm at the end of each day
- change liners between dives with a warm dry one
- enter water from a warm shelter
If the 2nd stage is free-flowing and cannot be stopped with adjustment of the dial-a-breath the helmet should be removed and gas supplied stopped until the housing is heated. The flowing gas will only cool the diaphragm more.
- keep the helmet harm between dives
- keep the diaphragm conditioned Exhaust valve freeze up before submersion (froze open or closed)
Due to the same reasons as above the exhaust check valve will often freeze open before entering the water. Stay at the ladder after submerging the helmet until the exhaust is working properly.
- remove housing and dry the valve at the end of each day
- change liners between dives with a warm dry one
Always be prepared to remove the helmet after locking down if exhaust is frozen closed.
Remove the helmet and warm until exhaust is free.
- keep the helmet harm between dives
- keep the diaphragm conditioned Ice in umbilical gas hose causing lose of surface supply
Compressed gas carries moisture which freezes at steal fittings causing pellets. These can completely block the flow in the hose or get caught in the helmet check valve, block, bent tube assembly or 2nd stage. If the diver identifies a loss of pressure or volume or ice pellets are felt coming through the oral nasal then the dive should be aborted. The secondary gas supply pressure should be maintained at 1.25 times the primary. If blockage occurs switching to secondary can pass the blockage. Insure the bailout supply comes into the block down stream of the check valve. This will allow the diver to go on bailout and free-flow if the check valve and 2nd stage are frozen.
- use water separates in the filter pack
- use dry bottles air kept warm
- avoid exposed fittings above water
- blow out hoses with bottled air at the start and end of each day (always point hose away from persons when blowing out, I’ve seen one lad with a ice pellet embedded in his hand).
- use hoses that are rated for cold weather (i.e. Barfeld diving umbilicals are rated to -10 o F only)Ice in pneumo causing loss of depth monitoring
Ice pellets can block the pneumo hose. Before each dive start a slow bleed on the pneumo keeping an eye on the gauge to avoid pinning. Stop bleed to check depth and then resume. A pressure relief valve at the gauge can avoid damage to the gauge.
- blow out pneumo hoses with bottled air at the start and end of each day.
- avoid fittings down steam of gauge
- use 3/8 ID hose that is rated for freezing conditionsStart up of equipment
Compressors and gas or diesel power plant start ups can be frustrating at best. Try to keep the compressor and powerplant warm after shut down. If not possible, remove the oil from engine and keep warm. Remove the belt from powerplant, start and warm up engine. Shut down and replace belt then start maintaining slow RPMs with outlet valve open until compressor is warm.
- keep warm when not running
- use block heaters on powerplant and compressor
- if possible use electric powerplantsProtection of surface crew from wind and cold
When surface temperatures are below freezing a heated shelter should be used to keep equipment and standby diver warm. A sea container, cube van or tent can be used. If the diver can enter the water without exposing equipment to freezing conditions many problems can be avoided.Getting and maintaining access to water
Use a chain saw with long bar and vegetable oil for chain oil to cut access. I prefer an equilateral triangle with minimum of 1 meter sides. Cover the hole with SM Styrofoam and snow at the end of the day to keep open or maintain a bubbler. I have an old buddy who jumped off a 6 ft. dock onto the hole after a one hour lunch and stopped. Ice can lay down fast in cold weather so always keep open.Moving ice
Moving ice can close the access hole or grab the umbilical. If the pack ice is moving the access hole should be shored up to prevent closing. Diving in a river with flowing ice should be considered too hazardous unless some type of diverter can be installed to eliminate ice flow from access to work site. Topside should always keep a lookout for hazardous moving ice conditions. . Moon-pools can become clogged and anchors could drag if the vessel is in moving ice. . Be prepared for moving ice when diving from a vesselGetting to dive site
If traveling on ice, thickness must be verified. Try to access the water as close to the divers work site as possible. This could mean cutting several holes say along a pipeline. In this case a shelter on skids or if ice conditions are good a cube van. If ice conditions are poor a shelter on a flat bottom steel boat that can be dragged over the ice will increase safety.Gas build up causing loss of ice bearing strength
If ice thickness is 2 feet or less or you are diving in the same location for several days divers exhausted gas can build up under the ice weakening bearing strength. This can also act like a bubbler thinning the ice. If gas is seen coming up through a crack be aware and identify thinning conditions.Predive planning and job hazard analysis
This will be the greatest line of defense against accidents. Everything takes longer to do in freezing conditions and this is no exception. Besides typical predive planning there are several other considerations:
- divers thermal protection
- identification of hypothermia or even hyperthermia
- extra weight needed if diving dry
- locating work site
- weather monitoring
- standby divers thermal protection
- monitoring ice conditions
- minimum 4 man crew (coffined access)
There are several unique hazards to analyze:Emergency contingency plan
It will take longer to transport injured personnel to shore and keeping them warm while transporting is a problem to be overcome. Here are some extra considerations:
- moving ice hindering access to shore
- freezing of access hole
- loss of divers gas supply
- compressor or equipment freeze up
- hypothermia management
- changing weather conditionsFilter packs, Regulators and racks freezing
If the filter packs are not located in a heated environment the moist elements will freeze and stop air flow or tear and send filter material into the rack. I have had a blockage at the helmet check valve due to filter debris. Moisture in the divers rack can freeze and block flow and HP regulators can freeze closed.
- keep the filter pack in a warm environment
- bleed filters regularly
- keep the divers rack in a warm environment
- keep secondary gas supply and regulators in a warm environment.
- Tee off of the bottle to two regulators for extra redundancy.
- use glycerin or cold weather gauges
- add a water separator before filtersPower tools freezing
Always try to use hydraulics in freezing conditions. Besides the start up of hydraulic pump and running a tool to warm up hydraulic oil there are no other concerns.
If pneumatics are the only choice,be prepared for freeze ups.
Here are some modifications that I have found to help:
- use an air heater down steam of the compressor
- use a mixture of ½ methalhydrate and ½ mineral oil for inline oiler.
- keep all pneumatic hoses above the water insulated
- run 2 tools to the job site, when one freezes use the other, when the second tool freezes the first should be thawed.Battery life of electrical equipment reduced
Freezing temperatures greatly reduce the working life of batteries.
- keep batteries in a warm environment
- keep spare batteriesIn water decompression hazards
Always decompress using Sur-D- O2 tables to minimize in water times. Be sure to have heaters for the chamber and warm blankets. Be aware of limitations with hot water suits.
Buffer 10 feet and 10 minutes due to off-gassing and larger buffer zone. Always blow down in inner lock for extra heat. Insure chamber has good structural bearing.Loss of hot water for hot water suits
This is as cold as I’ve ever been. Three minutes from loss of hot water to leaving the 31o F water. All was well below the rig in the Buford Sea, 2 seconds later all was not well. The shock even makes breathing difficult let alone talking. Top side told me to free flow because of my short rapid breathing when I’m trying to scream “up on slack”
Now I always wear a short under the hot water suit to give me some insulation. Hot water is awesome - Less to no weight,good off-gassing and great mobility. You can pay more attention to the job. Set up time is increased as well as E.C.P. and J.H.A.
If decompression diving, you need to have a heated reservoir with enough volume to complete the dive and water stops plus 25%. This often makes hot water suits unpractical for decompression diving. Always add extra buffers and be prepared for omitted decompression.
=================================And a note from Old Barnacle: And when all is said and done -something I learned as a kid in Northern Ontario - "Never ... and I mean NEVER .... lick a K-Cylinder at -30C!!!
Till next time ....