Professional Diving, Truth, and the Uncertainty Principle

Is anything known for sure?

Heisenberg’s Uncertainty Principle applied to quantum events avows that there is no certainty until you look. Well, this morning, I looked, and I’m just as confused as ever.

It was a chilly morning in late November. As we warmed up with coffee, I wondered how cold it was outside. So, in the modern style, my wife and I checked the Weather Channel on our phones. One indicated it was 47°F, but the other showed it was 48°F.

That can’t be, I said. So, with identical phones side by side, both tuned into Panama City Beach, Florida weather on the Weather Channel, one phone said it felt like 45°F, and the other said it felt like 43°F.

As Charlie Brown would say, “Good grief.”

Wanting to find some agreement among our devices, I checked a nested set of humidity and temperatures sensors grouped together in our kitchen. Humidity indicators are notoriously inaccurate, yet amazingly, the measured humidity was in reasonable agreement. But inside temperature varied from 70.3°F to 72.8°F.

According to Segal’s Law, “A man with a watch knows what time it is. A man with two watches is never sure.”

This aphorism is falsely attributed to Lee Segall of KIXL, now KGGR in Dallas. Regardless of the source, it is often repeated because it makes such good sense. If you multiply the number of devices three times, as above, the situation is no more precise. (But that’s where statistics comes in, I suppose.)

Giving up on simple things like local environmental parameters, I turned to the latest news on the VAERs update for the vaccines.

I wish I hadn’t. Yes, there is a chance you’ll be fine, but there’s also a small chance you’ll have heart problems and even a small chance you’ll die.

Frankly, my one-time shot at slot machines and the roulette table in Vegas did not end well. So, is there anything we know that can be guaranteed accurate?


I’ve spent a long Navy career in diving science, so I know there are serious certainties there. If you consume more air than is in your scuba tank, you’ll drown. If you stay down too long and surface too quickly, you’ll get the bends, aka decompression sickness.

But what if I use a decompression computer to plan my dive and follow its guidance to the letter? Unfortunately, there’s still a chance you’ll end up in a treatment chamber. Both people’s health and the water environment change constantly, and no decompression algorithm is perfect, or omniscient.

Undersea Oxygen Clinic, Tampa, Florida

From an engineer’s perspective, the tensile strength of a bolt is known within strict limits. If the force applied to that bolt exceeds its limits, then bad things might happen. Buildings might fall, or planes might crash. Or your muffler might fall off.

It’s hard to know what the effect of a broken bolt will be unless you understand precisely the function of that bolt. There is uncertainty in the outcome of a bolt breaking.

Uncertainty vexes some engineers to no end. I’ve watched them squirm as I reveal the role of statistics and probability in acceptance decisions about diving equipment. People are not bolts whose tensile and shear strength can be measured. As Heisenberg predicted (out of context), a dive outcome cannot be predicted with certainty.

Equipment Testing

The same thing applies to diving equipment. The Navy Experimental Diving Unit is entrusted with determining the safety and suitability of underwater breathing apparatus. Both physiologists and engineers envision a line in the sand for a given water depth and diver breathing rate.

If a UBA exceeds that line during testing, it should be rejected for military use. Right? After all, a limit is a limit.

Test and Evaluation Laboratory, Navy Experimental Diving Unit, Panama City, Florida. Photo by Stephen Frink.

Well, not exactly. When translating engineering limits into human terms, things get messy.  If a published limit is exceeded, just like taking the COVID vaccine, some people will fare well, while others may pass out. In other words, failure is classified as the probability of an untoward event where untoward translates to anything that threatens a diver or a diving mission.

For any given dive, and any given diver, the probability of a dive failure cannot be known precisely. Dive failure, like decompression sickness, is probabilistic.

One type of untoward event: Ice inside a second-stage scuba regulator.

To illustrate, the following table and text are from NEDU Technical Report 16-04, Physiological Event Prediction in Evaluations of Underwater Breathing Apparatus, October 2016.

Usually, a UBA evaluated at NEDU is suitable for most diving depths and any foreseeable work/ventilation rate, as shown in Table 1.

The only time that limits were exceeded was at the greatest depth and ventilation rate.

But what if the data had revealed a slightly larger “out of limits” region, as in the next table? What decision regarding safety would then be made?

Hypothetical Test Data

In this hypothetical case, human judgment is required. It is not sufficient to declare the diving equipment unsafe for use. It simply means divers need to pace themselves when working and breathing hard near a depth of 200 feet. Reducing their workload enough to slow their breathing to 62 liters per minute or less (still a high ventilation rate) is a safe way to keep the UBA within limits.  

This is nothing new. Every salvage diver knows to occasionally interrupt hard work periods with periods of rest. Catching your breath is kind of important.

Limits are not absolute

As a person with too many watches, or thermometers can attest, you can’t be sure what all the various goal numbers and limit numbers mean. Instead, collectively they should be used as a guide to safe diving.

Hanging on the umbilical in a KM 37.

Whether you’re a sport diver or professional, if an underwater breathing apparatus is functioning normally but doesn’t meet all of the EU (EN250) or U.S. Navy engineering limits under all possible testing conditions, that doesn’t mean it’s not a useful piece of diving gear. You just have to use it judiciously. After all, good human judgment is always required for safely operating life support equipment.

It is a wise diver who remains mindful of their life support system’s limitations and plans their dive to stay within those limitations. That way, the probability of experiencing an untoward event is minimized.

Authorized for Cold Water Service: What Divers Should Know About Extreme Cold

The following is reprinted from my article published in ECO Magazine, March 2015.  It was published in its current format as an ECO Editorial Focus by TSC Media. Thank-you Mr. Greg Leatherman for making it available for reprinting.ECO Magazine

It is the highpoint of your career as an environmentally minded marine biologist. The National Science Foundation has provided a generous grant for your photographic mission to the waters 100 ft below the Ross Ice Shelf, Antarctica. Now you’re on an important mission, searching for biological markers of climate change.

Under Antarctic Ice, photo by Dr. Martin Sayer.

Above you lies nothing but a seemingly endless ceiling of impenetrable ice, 10 ft thick. Having spent the last several minutes concentrating on your photography, you look up and notice you’ve strayed further from safety than you’d wanted. The strobe light marking the hole drilled in the ice where you’ll exit the freezing water is a long swim away. And, unfortunately, your fellow scientist “buddy” diver has slipped off somewhere behind you, intent on her own research needs.

You’re diving SCUBA with two independent SCUBA regulators, but in the frigid cold of the literally icy waters, you know that ice could be accumulating within the regulator in your mouth. At the same time, a small tornado of sub-zero air expands chaotically within the high-pressure regulator attached to the single SCUBA bottle on your back—and that icy torrent is increasingly sucking the safety margins right out of your regulator. You are powerless to realize this danger or to do anything about it.

At any moment, your regulator could suddenly and unexpectedly free flow, tumultuously dumping the precious and highly limited supply of gas contained in the aluminum pressure cylinder on your back. You’re equipped and trained in the emergency procedure of shutting off the offending regulator and switching to your backup regulator, but this could also fail. It’s happened before. 

As you try to determine your buddy’s position, you’re feeling very lonely. You realize the high point of your career could rapidly become the low point of your career—and an end to your very being. Picture046

The preceding is not merely a writer’s dramatization. It is real, and the situation could prove deadly—as it has in far less interesting and auspicious locations. Regulator free flow and limited gas supplies famously claimed three professional divers’ lives in one location within a span of one month.

There is a risk to diving in extreme environments. However, the U.S. Navy has found that the risk is poorly understood, even by themselves—the professionals. If you check the Internet SCUBA boards, you constantly come across divers asking for opinions about cold-watersafe regulators. Undoubtedly, recent fatalities have made amateur divers a little nervous—and for good reason.

Internet bulletin boards are not the place to get accurate information about life support safety in frigid water. Unfortunately, the Navy found that manufacturers are also an unreliable source. Of course, the manufacturers want to be fully informed and to protect their customers, but the fact remains that manufacturers test to a European cold-water standard, EN 250. By passing those tests, manufacturers receive a “CE” stamp that is pressed into the hard metal of the regulator. That stamp means the regulator has received European approval for coldwater service.

As a number of manufacturers have expensively learned, passing the EN 250 testing standard is not the same as passing the more rigorous U.S. Navy standard, which was recently revised, making it even more rigorous by using higher gas supply pressures and testing in fresh as well as salt water. Freshwater diving in the Navy is rare—but depending on the brand and model of regulator in use, it can prove lethal.

The unadorned truth is that the large majority of manufacturers do not know how to make a consistently good Performing cold-water regulator. Perhaps the reason is because the type of equipment required to test to the U.S. Navy standard is very expensive and has, not to date, been legislated. Simply, it is not a requirement.

Some manufacturers are their own worst enemy; they cannot resist tinkering with even their most successful and rugged products. This writer is speculating here, but the constant manufacturing changes appear to be driven by either market pressures (bringing out something “new” to the trade show floor) or due to manufacturing economy (i.e., cost savings). The situation is so bad that even regulators that once passed U.S. Navy scrutiny are in some cases being changed almost as soon as they reach the “Authorized for Military Use” list. The military is struggling to keep up with the constant flux in the market place, which puts the civilian diver in a very difficult position. How can they—or you—know what gear to take on an environmentally extreme dive?

My advice to my family, almost all of whom are divers, is to watch what the Navy is putting on their authorized for cold-water service list. The regulators that show up on that list (and they are small in number) have passed the most rigorous testing in the world.

Through hundreds of hours of testing, in the most extreme conditions possible, the Navy has learned what all SCUBA divers should know:

• Even the coldest water (28°F; -2°C) is warm compared to the temperature of expanding air coming from a first stage regulator to the diver. There is a law of physics that says when compressed air contained in a SCUBA bottle is expanded by reducing it to a lower pressure, air temperature drops considerably. It’s the thermal consequence of adiabatic (rapid) expansion.

• Gas expansion does not have to be adiabatic. Isothermal (no temperature change) expansion is a process where the expansion is slow enough and heat entry into the gas from an outside source is fast enough that the expanded gas temperature does not drop.

• The best regulators are designed to take advantage of the heat available in ice water. The most critical place for that to happen is in the first stage where the greatest pressure drop occurs (from say 3,000 psi or higher to 135 psi above ambient water pressure (i.e., depth). They do that by maximizing heat transfer into the internals of the regulator.

• First stage regulators fail in two ways. The most common is that the first stage (which controls the largest pressure drop) begins to lose control of the pressure being supplied to the second stage regulator, the part that goes into a diver’s mouth. As that pressure climbs, the second stage eventually can’t hold it back any longer and a free flow ensues.

• The second failure mode is rare, but extremely problematic. Gas flow may stop suddenly and completely, so that backup regulator had better be handy.

• Second stage regulators are the most likely SCUBA components to fail in cold water due to internal ice accumulation.

• Free flows may start with a trickle, slowly accelerating to a torrent, or the regulator may instantly and unexpectedly erupt like a geyser of air. Once the uncontrolled, and often unstoppable free flow starts, it is self-perpetuating and can dump an entire cylinder of air within a few minutes through the second stage regulator.

• A warm-water regulator free flow is typically breathable; getting the air you need to ascend or to correct the problem is not difficult. In a cold-water-induced free flow, the geyser may be so cold as to make you feel like you’re breathing liquid nitrogen and so forceful as to be a safety concern. Staying relaxed under those conditions is difficult, but necessary.

• Water in non-polar regions can easily range between and 34°F to 38°F; at those temperatures, gas entering the second stage regulator can be at sub-freezing temperatures. European standard organizations classify ~10°C (50°F) as the cold/non-cold boundary. The Navy has found in the modern, high-flow regulators tested to date that 42°F is the water temperature where second stage inlet temperature is unlikely to dip below freezing.

• The small heat exchangers most manufacturers place just upstream of the second stage is ineffective In extreme conditions. They quickly ice over, insulating that portion of the regulator from the relative warmth of the surrounding water. Heat Ex Regulator

• Regulator “bells and whistles” are an unknown and can be problematic. Second stage regulators with multiple adjustments can do unpredictable things to heat transfer as the diver manipulates his controls. The last thing a cold-water diver should want is to make it easier to get more gas. High gas flows mean higher temperature drops and greater risk of free flow.

• Only manufacturer-certified technicians should touch your regulator if you’re going into risky waters. The technician at your local dive shop may or may not have current and valid technician training on your particular life support system. Don’t bet your life on it— ask to see the paperwork.

• Follow Navy and Smithsonian* guidance on handling and rinsing procedures for regulators in frigid waters. A single breath taken above the surface could freeze a regulator before you get your first breath underwater.

U. S. Navy reports on tested regulators are restricted. However, the list of those regulators passing all phases of Navy testing is available online. If your regulator, in the exact model as tested, is not on that list, do yourself a favor and don’t dive in frigid waters.


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The original Editorial Focus article is found in the digital version of the March ECO magazine here, on pages 20-25.