USN Mark I Mod 0 Wrist Depth Gauge - Information?

[admin]

Here are some photos of a wrist depth gauge that I recently added to my collection. I've never seen one of these before, and perhaps someone can give me some more information as to when it was issued and what exactly was it designed for. The metal case is stamped "USN-Wrist Depth Gage, Mark I Mod 0 SER NO 2575/59 BENDIX FRIEZ". The decal on the bottom reads "Danger Caution Radioactive Material THALLIUM 204 1.6 Millicuries". The dial reads from 0-20 - possibly meters? Is the radiactivity because of the illuminated dial?
Dan

[YankDownUnder]

Let me venture an educated guess.

The calibration is probably in meters. La Spirotechnique makes a similar one, one of which is on the UK ebay now. They were made for military use. I have a La Spirotechnique, which I use with my shallow water rebreathers. The ebay seller only knows part of the story. The shallow water depth gauges are calibrated to give the diver a more sensitive depth reading as depth is more critical with high oxygen partial pressures. They are used for either 100% oxygen to 10 meters, or 60% oxygen (EAN60). EAN60 allows the diver to go to 17 meters for combat operations and deeper for short periods. There are still bubbles, but they are minimal. The new rebreathers, such as the Drager LAR 7, allow the use of either mixture, and have a diffuser to release only very small bubbles. The 'combi' version allows for the underwater change of gas.

Even in the 1950s, this was a common military practice and the Royal Navy's Avon CDBA could be used with 60% or 100% oxygen. The diver carried twin aluminum tanks behind him, which could be use with oxygen or EAN60. His front belly tanks carried oxyen only. He could thus change from one to another underwater.

The radiation warning is affixed as the military was, and is allowed to deviate from radiation standards. Early night sights on M16 rifles were radio-active, as were some watches. Many years ago, most watch dials were radio active, and were banned, because of the dangers of cancer. The radio-active isotope gives continuous bright numerals.........and cancer, with prolonged use.

Do not, repeat do not, allow the isotope to be broken.

[SeaRat]

The banning of the radioactive, luminous materials for watches and depth guages was not until fairly recently. I remember having some in the Pararescue units in the 1967-1970 era. But the main problem is not for the diver, but for the person who must put the materials onto the watch or depth guage or compass (I think ours were on compasses). The people in the factories were the ones coming down with the cancer, as this was applied by hand, and sometimes the people, in order to get the brush sharper, would put it in their mouth. Those were the people who really suffered from the radioactive materials on these guages. See:

en.wikipedia.org/wiki/Radium

en.wikipedia.org/wiki/Radium_Girls

John

PS--this was worse than I thought, with some of the Radium Girls painting nails, face and teeth with radium powder-impregnated paint...bad, bad news. jcr

[Captain]

The gauge is explained in detail in the 1970 edition of the U S Navy diving manual. The indicating dial contains 1.6 millicuries of radioisotope thallium. Radiological contamination hazard exist if the dial is damaged in any way that permits contact with the radioiactive compound. The dial readingis divided into 20 equal divisions with each division representiog 10 feet. To obtain actual depth multiply the dial reading by 10. It is non magnetic. If you want more information I can copy the pages from the manual and send them to you. It does not appear in my 1958 edition of the manual.

[SeaRat]

Tom is right, as I also have the 1970 Edition of the US Navy Diving Manual, and the explaination is on page 544. Here is what the manual states:

Radioactivity
Tthe indicating dial is a sealed source containing approximately 1.6 millicuries of radioisotope thallium-204, a pure beta emitter, in the form of thallus molybdate. Radiation intensity, at the surface of the dial, is approximately 1 mr/hr. Radiological contamination hazard does not exist as long as the dial (sealed source) remains intact. Radiological contamination hazard does exist if the dial has been damaged in any manner that permits contact with or ingestion of the radioactive compound by personnel. For this reason, the gages must be periodically inspected or radiological contamination, and usid and handled in accordance with Atomic Energy Commission regulations. Detailed instructions for these procedures are issued by NAVSHIPS. The dial bears the AEC conventional radiation symbol. This symbol and other pertinent radioisotope data appear on the back of the gage. These markings must not be obliterated or removed from the gage. Gages are free from radiological contamination when elivered by the manufacturer to the supplying activity.

Part of the studying that I am doing, which limits my coming to this site, is the physical hazards of the worker's environment, and ionizing radiation is one of those hazards. The above quote states that this is a pure beta emitter. One of my sources that I'm studying (The Occupational Environment, It Evaluation, Control and Management) states, "A 10-MeV electron (or beta) will penetrate the skin to about 5 cm." So those beta particles coming off the face of the gage could penetrate into the body a considerable distance.

Now lets look at the potential for exposure to a diver for the intact gage. The "Threshold Limit Value" (TLV)* for radiation is measured in units of millisieverts (mSv). 10 mSv is equal to 1 rem. The TLV for ionizing radiation is 50 mSv, or 5 rem. The Mk1 Mod 0 gauge (using normal English now) has 1.6 millicuries and emits 1 millirem (mrem) per hour.

TLV = 50 mSv/year = 5 rem/year = 5000 mrem/year
To reach the TLV, a diver would need to wear (upside down) the gauge for a period of time. Here's that calculation:

TLV for a year = 5000 mrem / 1 mrem/hour = 5000 hours, or 208.3 days of continuous wearing of the gauge (upside down, of course).

This is why the intact gauge is not a hazard. But, if the case is broken, the material can get on the outside of the case. The probability is then to contaminate the hands, and get this stuff (thallium-204) into the body through either the nose, mouth (by eating something like a sandwich), or into the lungs by smoking a cigarette with contaminated fingers. Here, the beta particles are inside the body, and will potentially stay there for an extended period (perhaps years).

Dan, here's the diagram from the US Navy Manual of the workings of this gauge:

It looks clean, although the outside of the face is discolored, but before I handled it much, I'd have it checked out for leakage. I would also wash my hands after handling it just in case.

John

PS--I did have to study a bit for my exam (this stuff is on it) in order to write this;)

*American Conference of Governmental Industrial Hygienists' Threshold Limit Value Booklet, 2004

[luis]

That is why it is a bad idea to eat your gauge





This drawing is in the owners manual of a dive timer I own.

[duckbill]

Dan,
That gauge sounds much too dangerous. If you want to get rid of it, let me know I just didn't bid enough on it the first time around

[mudhog]

Thanks to all for posting, has been a good read.

[admin]

Thanks guys for the great input and feedback. I do have the 1970 USN Dive Manual but I never even thought to look there. For some reason, I thought this gage was newer- maybe from the 1980's or 90's. But Vietnam era is better- it will fit in with my non-magnetic AquaMaster and non-mag tanks for a great display. Terry- are you the guy I beat out on this gage by .02 cents? Sorry!
Dan

[duckbill]

admin said:

Terry- are you the guy I beat out on this gage by .02 cents? Sorry!
Dan

Actually, no. In fact I didn't notice 'til you mentioned it that your bid won by 2 cents! If I recall correctly, I bid a little less than the runner up just a second or so after he placed his bid, so my bid was covered by his and my bid doesn't show as a result. Just goes to show that sometimes there can actually be more biders than what the bid history shows.
Congratulations! I'm glad you got it. I've had fun just reading about it here, and it went to a very good home. I, too, assumed the divisions were meters. Tens of feet makes much more sense.

[johnblickle]

Dan, that gauge is really a nice find. It looks like it is excellent condition. I suppose that there are very few around because of a possible radiation issue.

There is not a significant radiation risk with your gauge. SeaRat’s sectional view shows that the thallium source is itself sealed inside the gauge and imbedded in the white ring that is under the numbers as shown in your photo. The electrons from the source must have made the white ring glow and the numbers could then be seen backlighted. Even if the gauge housing leaked, the source was designed to be contained.

More importantly, thallium 204 has a halflife of 3.77 years. SeaRat’s information indicates that gauge was made no more recently than 1970. Even assuming 1970 for a production date, almost all of the thallium has decayed away to lead 204 with a very small fraction to mercury 204, both stable isotopes. The strength of the thallium radioactivity has decreased by about three orders of magnitude; it is now perhaps a couple of microcuries. And of course if the gauge is older than 1970 the thallium source is even weaker.

Can you see any glow, even with dark-adapted eyes?