Silt Out - Wreck Danger! A graphic video demonstration.

[Belmont]

When I was a student, long ago, my hobby was photography. I would spend long hours in a darkroom. Maybe this was helpful in making me used to moving and handling things in obscurity.

There is a switch that goes out in my head when I'm in total darkness. I, its hard to explain, turn my attention inward and focus on my sense of touch and I view the surroundings in my mind. This way I keep calm, it gives me a virtual base to grab on an keep away any feeling of panic.

The sense of sight is our most used one, when we suddenly lose it our it our brain has difficulty in handling the loss of input.

On a similar note: we have a restaurant in Montreal where you eat in total darkness. The personnel is composed of blind people and they serve you in a darkened dining room. It's a special experience, we realize how much we rely on our sense of sight even for the simple activity of eating.

Restaurant O.Noir Montreal. Mangez dans le noir. Dine in the dark.

For cave and wreck training it might be instructive for the students to be blindfolded in the classroom spun around a few times and told to find the exit.

 

[GoProHonduras]

Nice training aid DD, permission to show in our wreck specialty/MSDT training?

@Belmont, I ate in that restaurant, you think you're doing good, till you take a forkful of goat cheese instead of mashed potato!

 

[DA Aquamaster]

It's terrifying how disorienting zero vis can be. I have experienced it a few times in our local lake. It caused me to feel very uneasy the first time it happened. I couldn't even read my computer to judge my depth. Now that I've experienced it a few times, I have a lot more respect for the dangers in a cave from zero vis.

Like Belmont I was also an avid photographer from High school onward and until the dawn of the digital SLR age, I spent a good deal of time in the darkroom.

I think he does a good job of describing how I react to dark as well. Even in almost zero viz, I close my eyes to reduce the distraction of non-useful visibility (but open them regularly to check for improvement), it really helps the inward focus.

I was also very fortunate in the sense that I started doing inland commercial diving from 1978 through 2005 - well before I started cave training.

Since a large majority of the commercial diving done in heavily silted areas will be zero viz, you get really good at maintaining orientation, and buoyancy with no visual reference, and you do that by noting some of the more subtle cues available, such as differential pressure over your body in a dry suit when not perfectly horizontal, the direction of the bubbles leaving the second stage, how they sound when moving away from you in different directions, and the evenness of the up and down motion that comes from inhaling and exhaling at neutral buoyancy versus being slightly heavy or light. In terms of orientation you learn some tricks such as placing a hand and rotating around it to rely on kinesthetics to make and track changes in direction. Having very good spatial skills and being able to develop and maintain an accurate mental map also helps a lot and lots of zero viz diving helps you develop what ever spatial abilities you have.

The hundreds of hours of working in zero viz along with lots of experience in dry suit and doubles meant that when I got to my cavern course, I was rock solid in blacked out mask or lights out drills. Those zero viz, orientation and spatial skills are still beneficial in terms of reading a cave on the way in, then being able to reverse the mental map and accurately interpret the map and anticipate what should be coming up during a zero viz exit. I still find that to be very handy post full cave in small, tight, silty sidemount caves where a low viz or even zero viz exit is very likely and often inevitable.

 

[CT-Rich]

...
Technically... it was 3 small kicks (from a Force Fin) directly into the silt. It probably equates to much less than I've seen recreational divers do in open-water when they have a buoyancy melt-down in vertical trim near the bottom...

Really, if you think about a panic responce from an unprepared diver trying to make a power shot through the door, you were generous with your students. one diver spinning around to unhang himself from an obstruction will probably screw the pooch on visibility much faster than your baby kicks did... and his gear would still be hooked on whatever was behind him.

of course, low vis like that is called a good day of diving in Long Island Sound...

 

[Mr. Willoughby]

Good video. It illustrates your point very well. Zero vis situations are tense enough without the added pressure of having to worry about students.

 

[DevonDiver]

Really, if you think about a panic responce from an unprepared diver trying to make a power shot through the door, you were generous with your students. one diver spinning around to unhang himself from an obstruction will probably screw the pooch on visibility much faster than your baby kicks did... and his gear would still be hooked on whatever was behind him.

That's one issue that many novice (wreck) divers fail to appreciate. In a short training course, it is possible to stress (and teach) the need for superior buoyancy, trim and propulsion technique. For as long as the student is permitted to focus upon those requirements, they will maintain a satisfactory performance and probably not cause silt disturbance.

However, unless those fundamental competencies are fully ingrained and automatic (something not achievable in 4-dives of training IMHO) then they will perish whenever the student is forced to transfer their focus to another requirement. Line laying is often sufficient over-load to cause those core skills to perish - where the student loses focus on silt-avoidance... with obvious repercussions. More dramatic sensory inputs - for instance, air-sharing, entanglements or light failures, cause a more significant overload and often lead to subsequent silt issues.

With teaching experience, what I've found is that most recreational divers will resort to a vertical dive trim when task-loaded. Only specific foundational/fundamental core training can remove this tendency....along with considerable experience applying that training over time..to ingrain it as an unconscious and automatic state. Most divers can quickly adopt a suitable horizontal trim, good buoyancy and non-silting propulsion in a short time-frame with decent instruction. However, most divers need to focus on maintaining that for quite a time after they learn it. Successful and safe diving in silt-hazard overhead environments demands that the student should reach a level of proficiency where focus is no longer needed to retain that state.

For me, silt education is about reality. Most recreational-trained wreck divers won't have ingrained foundational skills... or the subsequent ability to retain buoyancy/trim/propulsion to avoid silt-out if presented with any alternative demands or distractions. 4 wreck training dives is not sufficient to remediate that. My goal is to educate that reality - so that the student can address the problem over the long term (via further training and self-practice). In the meantime, that education is linked to a realistic awareness of the consequences of silt-out... the lesson being to avoid penetrations where the diver could silt-out should any distracting incident or task occur.

of course, low vis like that is called a good day of diving in Long Island Sound...

In the case of my video, the silt was still 'blooming' when we exited. It was 'chasing' us out... and it hadn't fully risen to obscure the overhead portholes. I find that sufficient, at recreational level, to teach the lesson, whilst retaining an element of safety and comfort. Another 90-120 seconds (after leaving that compartment) the silt has fully filled the area and visibility is truly zero (can't read illuminated gauges pressed against mask in any area of the compartment). Students learn what a silt-out means.... how a silt-out behaves (how it rises and fills) and what sort of time-frame they have to react/egress from the area before safe levels of visibiility are lost.

 

[Kevrumbo]

After twenty days diving the nearly 70 year old WWII wrecks of Chuuk Lagoon, I've learned that in a wreck"s engine room with many surfaces to accumulate silt (i.e. metal shelves; pipes; machinery; large levers & control wheels, dials, guage faces etc) along with percolation from exhaust bubbles, you are going to have a silt-out of varying degrees in a short time, no matter how careful your frog-kick finning or even with just a simple pull & glide technique with your hands. For these wrecks and for this reason, a two-person team is preferable over three, and in lieu of running a primary reel line, a known traverse pathway through the superstructure with a large exit showing lots of outside ambient is desirable as well. . .

The best technical wreck training I ever had for these type of Indo-Pacific WWII wrecks was at Subic Bay Philippines six years ago, in which the Instructor deliberately silted-out the overhead (a widebody cargo airliner fuselage at barely 6m/20') by kicking it up at the entrance. . .

http://www.scubaboard.com/forums/wr...al-wreck-course-subic-bay-25-30-nov-06-a.html

 

[Griffo]

This is the video that convinced me to not attempt the local wrecks until better trained, despite my rec agency "wreck" certification.

https://www.youtube.com/watch?v=oLtSmpBoRWE

The silt-out isn't as bad as that first video, but you can hear the increase in the respiration rate due to stress.

 

[CT-Rich]

This is the video that convinced me to not attempt the local wrecks until better trained, despite my rec agency "wreck" certification.

https://www.youtube.com/watch?v=oLtSmpBoRWE

The silt-out isn't as bad as that first video, but you can hear the increase in the respiration rate due to stress.

this goes well with another thread about a newbie that thinks he could swim Devils eye to Devils ear. even though it is, as you point out, a steel tube, it does show how disortienting an challenging a enclosed situation can be.

 

[Searcaigh]

When I worked offshore back in the 80s I had to do a survival course that included going through a maze built into a container that was smoke filled. Of course we had to wear breathing apparatus (same as fire fighters) and we had a time limit in which to enter and exit the smoke filled container.

Different from diving I know, but remembering some information from a great friend of mine, who was a fireman in Glasgow, describing how they tackled smoke filled buildings paid off big time for me passing that course.