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.


Cold Water Regulator Blues

It’s a black art, the making of scuba regulators for use in polar extremes; or so it seems. Many have tried, and many have failed.

Once you find a good cold water regulator, you may find they are finicky, as the U.S. Navy recently discovered. In 2013 the Navy invested almost two hundred hours testing scuba regulators in frigid salt and fresh water. What has been learned is in some ways surprising.

Looking at a pony bottle that saved a diver when both his independent regulator systems free-flowed at over 100 feet under the thick Antarctic ice.

DSCN3557cropThe Navy has been issuing reports on cold water regulator trials since 1987. In 1995 the Navy toughened its testing procedures to meet more stringent diving requirements. Reports from that era are found at the following links (Sherwood, Poseidon).  (Here is a link to one of their most recent publicly accessible reports.)

The Smithsonian Institution and the Navy sent this scientist to the Arctic to help teach cold water diving, and to the  Antarctic to monitor National Science Foundation and Smithsonian Institution funded trials of regulators  for use in the under-ice environment. What those studies have revealed have been disturbing: many regulator models that claim cold water tolerance fail in the extreme environment of polar diving.

The Navy Experimental Diving Unit (NEDU) has developed testing procedures that are more rigorous than the EN 250 tests currently used by European nations. (A comparison between US Navy and EN 250 testing is found on this blog). All cold water regulators approved for U.S. military use must meet these stringent NEDU requirements.

Nevertheless, we learned this year, quite tragically, that the Navy does not know all there is to know about diving scuba in cold water.

For example, what is the definition of cold water? For years the U.S. and Canadian Navies have declared that scuba regulators are not likely to freeze in water temperatures of 38° F and above (about 3° C). (The 1987  Morson report identified cold water as 37° F [2.8° C] and below). In salt water that seems in fact to be true; in 38° F scuba regulators are very unlikely to fail. However, in fresh water 38° F may pose a risk of ice accumulation in the regulator second stage, with resultant free-flow. (Free-flow is a condition where the gas issuing from the regulator does not stop during the diver’s exhalation. Unbridled free flow can quickly deplete a diver’s gas supply.)

The regulator on the left free-flowed, the one on the right did not.

While a freshly manufactured or freshly maintained regulator may be insensitive to 38° F fresh water, a regulator that is worn or improperly maintained may be susceptible to internal ice formation and free-flow at that same water temperature. There is, in other words, some uncertainty about whether a dive under those conditions will be successful.

IsolatorValve1 crop
An isolator valve that can be shut to prevent loss of gas from a free flowing regulator.

That uncertainty can be expressed by a regulator working well for nine under-ice dives, and then failing on the tenth. (That has happened more than once in Antarctica.)

That uncertainly also explains the U.S. Antarctic Program’s policy of requiring fully redundant first and second stage regulators, and a sliding isolator valve that a diver can use to secure his gas flow should one of the regulators free flow. There is always a chance that a regulator can free flow in cold water.

A key finding of the Navy’s recent testing is the importance of recent and proper factory-certified maintenance.  Arguably, not all maintenance is created equal, and those regulators receiving suspect maintenance should be suspected of providing unknown performance when challenged with cold water.

This finding points out a weakness of current regulator testing regimes in the U.S. and elsewhere. Typically, only new regulators are tested for tolerance to cold water. I know of no laboratory that routinely tests heavily used regulators.

Weddell seal on the Antarctic sea ice. Photo copyright Samuel Blanc. (From Wikimedia Commons).

Considering the inherent risk of diving in an overhead environment, where access to the surface could be potentially blocked by a 1400 lb (635 kg), 11 foot (3.4 m) long mammal that can hold its breath far longer than divers can, perhaps it is time to consider a change to that policy.

About to descend through a tunnel in 9-feet of ice on the Ross Ice Shelf.


A huge Weddell Seal blocks the diver’s entry hole. He looks small here, but like an iceberg, most of his mass is underwater.