If this crab had read this footnote, its tragic demise would have been avoided…
Commercial divers use the phrase ‘Delta P’ (or sometimes just ‘DP’) as a shorthand for ‘Differential Pressure’, to describe a potential diving hazard in which there is water movement from an area of higher pressure to an area of lower pressure. The term is a somewhat ominous one, being a culprit in two out of three commercial diving fatalities.
Situations in which a diver must prepare for a Delta P hazard include diving conditions where:
- water levels differ in adjoined regions and are attempting to equalize
- water is being drawn through or towards intakes, pumps, impellers, or thrusters
- water is adjacent to a gaseous void at lower pressure than the water
The trouble is, it can be impossible to recognize a dangerous Delta P situation visually. If you don’t believe me, take another look at the swift departure of that crab earlier!
So when commercial divers are required to undertake a task potentially involving a Delta P situation, calculations based on fluid mechanics must be made to determine the safety zone around the flow region. Three equations you’ll definitely need to familiarize yourself with if you want to understand the mathematical models behind these calculations are the Continuity Equation, Torricelli’s Equation, and the Drag Equation. But I’ll save a discussion of those equations for future, more mathematical, footnotes 😉
The following hard-hitting video is presented to commercial divers as part of their training, and describes the tragic details of 12 actual DP deaths. Of course, the hazard doesn’t only occur in commercial situations; many DP fatalities occur in domestic swimming pools, and even spas. So you don’t need to be a commercial diver to learn the lessons from this video…
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