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[Music]
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this is a partial list of the commercial
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diving fatalities over the past 15 years
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all have one common cause Delta
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P two out of three commercial diving
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fatalities involve Delta P it is
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invisible to a diver and it strikes
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suddenly without warning There is almost
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no way to escape once it grabs you
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knowing what it is where it lurks and
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how to avoid its grasp is the subject of
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this
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[Music]
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video Delta P stands for differential
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pressure our discussion refers to
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situations where the pressures between
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two bodies of water are dramatic
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different in a situation like this the
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bodies of water continuously seek to
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equalize themselves in this example the
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body of water on the right wants to rush
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to the body of water on the left by
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means of the pipe between them the
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pressure exerted on the valve stopping
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this water transfer can be enormous
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depending on the difference in the
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depths of the water and the diameter of
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the pipe if the difference between the
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depth of water is 50 ft and the diameter
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of the pipe is 10 in the force of water
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exerted on the valve is nearly 1,700
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lb if the valve was suddenly opened and
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your arm was near it would be sucked
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into the hole
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instantly trying to remove your arm
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would be like trying to lift a car
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completely off the ground with one hand
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you could only remove your arm if the
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pressures between the two bodies became
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nearly equalized but at the pressure in
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this example your body makes a perfect
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seal stopping the bodies of water from
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equalizing the formula for calculating
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the force of water through a hole at a
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particular depth
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is the area of the
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hole multiplied by the difference in
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water depth multiplied by the PSI per
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foot of water depth or in the situation
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just described the 10-in hole equals 78
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square in time 50 ft of water depth time
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0.432 PSI per foot of freshwater depth
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equals
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1,685 lb of water pressure if you are
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diving in saltwater be sure to use
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0.445 PSI in your formula
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instead you can't see or feel a Delta P
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situation as you dive near it it grabs
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you suddenly and it doesn't let go until
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the pressure is equalized when it's got
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you it's
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gotcha as you watch the following
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Recreations of actual Delta P incidents
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ask yourself if you have on occasion
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ventured into situations without being
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thoroughly
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prepared diver 1 enters theall Water
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behind the dam structure in order to
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clean the strainer of the Dam's drain
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when the drain is cleared the tremendous
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force of Rushing Water through the drain
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grabs hold of diver 1 sucks him
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partially inside and traps him diver 2
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enters the water to help diver 1 and
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becomes trapped
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also diver 3 enters the water to rescue
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divers 1 and two and after 40 minutes
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returns to the surface with both divers
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they are
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dead diver 3 was hospitalized for
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injuries suffered in the rescue
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[Music]
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attempts a scuba diver was repairing a
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pool bottom at a depth of 10 ft he came
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close to the open pool drain and was
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drawn against it his body made a perfect
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seal against the drain he was diving
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alone and had no tender at the surface
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no one knew he was trapped he ran out of
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air and
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[Music]
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drowned two scuba divers entered a water
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tower to unclog a drain using a fire
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hose to blast away the silt and mud that
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was clogging the drain the drain
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suddenly opened a great suction
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immediately occurred diver 1 was pulled
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into the drain visibility was Zero diver
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2 did not know that this had occurred
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diver 2 surfaced Thinking diver 1 had
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already come up diver 2 made repeated
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but unsuccessful attempts to find him
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diver one ran out of air and died
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neither diver was Tethered to the
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surface had communication with the
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surface or with each other
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[Music]
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a surface Supply diver was working
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offshore in 86 ft of water on a well
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re-entry project he was using a drill
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string to hook a trash cap inside a
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13-in well casing the first attempt
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failed to catch the cap the diver was
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asked to stand by the hole to make sure
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the string caught the cap he reported
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when he saw the cap was hooked and began
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to leave the drill string was pulled to
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the surface rapidly because the cap was
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nearly the size of the casing a great
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suction developed as the cap came free
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the Rushing Water grabbed the diver and
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forced one leg into the hole up to the
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pelvis the diver was
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[Music]
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killed diver one enters the water at a
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hydroelectric generation plant his
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assignment is to seal off leaks in a
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large gate valve the three-person dive
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team is assured by the plant's operating
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Personnel that the gate valve is closed
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diver one surfaces and reports that he
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thinks the valves are
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open the winch is started and closes the
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valve a 30-in SLO gate is manually crank
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shut the dive team questions the plant
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personnel the valve indicator shows the
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valve not fully closed plant Personnel
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reply that the indicator is never
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correct and typically the valve is
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cranked until tight diver 1 re-enters
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the water convinced that everything is
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okay in a few moments he begins to
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scream the dive supervisor tries to
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contact diver one on the intercom the
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tender and supervisor pulled the
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lifeline and umbilical both have broken
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from their attach match points the gates
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are cycled open while waiting for the
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rescue divers two attempts by the
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company diver failed to locate diver 1
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12 hours later diver 1's body is
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[Music]
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recovered when you accept a new job make
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sure you take part in a pre-job meeting
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again how are you right good be sure
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that you understand the layout of the
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site and how the piping and valve
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systems work
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together the diving supervisor should
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have a simplified but site specific
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schematic of the site and a diving
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checklist to make sure nothing is on or
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open that shouldn't
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be your client also needs to know about
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delap P if they take your concerns
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lightly make sure they understand the
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life-threatening hazard
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always practice lockout tagout
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procedures these are tried and true
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methods that can eliminate machinery and
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valve accidents if practice
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religiously make sure to consider the
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potential Delta P hazards of your new
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assignment when choosing your
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equipment make sure others in the water
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and on the surface can tell exactly
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where you are they should be able to
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communicate with you at all times and be
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able to get you out if you're
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stuck make sure your equipment won't
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interfere or become fouled if you must
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be near a Delta P
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situation there are certain techniques
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that you can use to help reduce and even
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eliminate delt P hazards the first step
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is to recognize the potential forces
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working on each other in your
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environment learn the layout of the site
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and how the system
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functions calculate the force of water
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at the depth you're working based on the
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size of the openings at that
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depth instead of cutting holes to drain
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water or relieve pressure cut slots if
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your body or equipment can't make a good
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seal against the flow of water you can't
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get
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stuck fabricate a cover for the drain
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that has a screen or make a cover that
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has more than one hole a good distance
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away from the other the idea is the
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water can still get through even if your
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body gets in the
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way the goal of this video is to make
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you aware of the potential for
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differential pressure situations the key
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is to recognize them beforehand and make
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sure you are prepared to deal with them
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because when it's gotcha it's
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gotcha don't add your name to this list
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[Music]
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[Music]
