Post by SeaRat on Jun 15, 2006 21:34:27 GMT -8
Many of you know that I have been studying for a professional exam all Spring. Well, I took the Certified Industrial Hygienist exam, and while I did better than I did twelve years ago, I did not pass it. So I’m continuing my studies, and actually enjoying the exercise of my mind. I came close, with a score of 59.1 for the 7 hour test. Passing was just a bit higher, at 62.3. The passing rate was 49.1% of those who took the Spring exam. So I’m in good company.
Why talk about this with you? Well, my fascination with science, and therefore what I have done professionally, springs from my love of diving in my teenage years. This is what got me into zoology, and into safety. From safety, I became fascinated with how people not only get hurt at work, but how they develop diseases. My first encounter with this was in my diving, where we learned about the direct and indirect effects of pressure on the human body. So now, I’m continuing to learn in chemistry, toxicology, physical hazards (lasers, UV and IR radiation, ionizing radiation, etc.).
Part of this had to do with learning how to compute the amount of chemicals in a room. How does this relate to diving? Well, a while back on a different site, there was talk about reconditioning an old underwater habitat. I had to caution this this was a confined space, and removing paint with chemicals could be hazardous.
But what does this have to do with vintage diving. Well, we learned again about Boyle’s Law, Charles Law, the Ideal Gas Law, and the Combined, or Universal Gas Law. After taking the test, I decided to use these to find out something I had forgotten—the volume of my twin –steel tanks. I had described them as twin 40s, and twin 42s, in various entries at this site. But I really did not know what they were, as the original documentation had been lost. These tanks were sold by Sherwood, I think, as I bought them through a LDS in Roseburg, Oregon with a Sherwood valve. They are stamped “DOT-3AA1800” with the numbers on each tank of “HC263461” and “HC263893.” And then they have their original hydro date of 7/\78 and 8/\78, and I have had them hydroed every 5 years since, including last year. They are unique, in that they have a concave bottom which does not need a tank boot to stand up on its own.
So I decided to use some of the renewed physics skills I have acquired this year to find out the exact volume of these tanks. To do that, I had to fill them with a known quantity of air. I figured that I could calculate this by using one of my single Al 80 tanks, filled at 3000 psi, to determine their exact volume. I wanted to start with a 3000 psi fill on the single Al 80, as that way I would have 80 cubic feet to work with.
To do this, I set my double tank unit up with yolk connector that we use to make doubles out of single tanks. I had to place my set of doubles on a folding table that was unrolled to the correct height, and then had to replace an O-ring on my single 80 before I got the connection right. I used my Trieste II with the Suunto Cobra pressure gauge (accurate to plus or minus 2 psig) on the yolk to make the last connection, and provide the correct psi readings. Here’s what it looked like:
And here’s a top view of the connections. With this setup, I was able to equalize the pressures between the empty twins and the single Al 80.
First, I thought that I could use 3000 psi for the fill, but I had taken the tanks apart for their annual VIP, and put them together again. I started filling them with the 3000 psi tank, only to remember that I had a very slight leak in the manifold. I stopped the fill about 15 seconds into it, bled the set dry, then took my huge crescent wrench and tightened the connecting nuts. Then the tank pressure read 2865 psi. So I needed to make a correction:
80 ft3/3000 psi = X ft3/2865 psi
X = 80 ft3 x 2865 psi / 3000 psi = 76.4 ft3
But in thinking this through, I decided that the 80 cubic foot designation was most probably at what we in the industrial hygiene world call “Normal Temperature-Pressure,” or NTP. NTP in American Standard units is 537 degrees Rankine (77 degrees F + 460 to get the temperature in Rankine units, which in the U.S. Navy Diving Manual, March 1970 is called “Absolute” temperature), and 29.92 inches of water for the air pressure (one atmosphere, if you will). The air pressure doesn’t matter in this calculation, as I am only a few hundred feet above sea level. But I was not working at 77 degrees F, and so I decided to calculate the volume difference at 65 degrees F (my garage temperature). The calculation is:
P1V1/T1 = P2V2/T2, but P1 and P2 are the same, so
V1/T1 = V2/T2, or 76.4 ft3 / (77 + 460) = V2 / (65 + 460)
V2 = 76.4 ft3 x 525 / 535 = 74.69 ft3
So I was starting with 74.69 cubic feet of air in the single Al 80 tank, at 2865 psi. I cracked the valve, and let the two systems equalize. I then let them sit overnight, with the valves turned off (in case of some leaks) to allow them to reach temperature equalization too. Then I read the pressure, and I was surprised. It read 959 psi in both tanks. Excited now about this finding, I ran the following quick calculation:
74.69 ft3 / 2865 psi = X ft3 / 959 psi
X = 74.69 ft3 x 959 psi / 2865 psi
X = 25 ft3
So what had happened is that 74.69 ft3 minus 25 ft3 = 49.69 ft3 transferred to the twin tanks at 959 psi. What is that at its rated 1800 psig rating:
49.69 ft3 / 959 psi = X ft3 / 1800 psi
X = 49.69 ft3 x 1800 psi / 959 psi
X = 93.27 ft3 = 93 ft3
So my small doubles were twin 47 cubic feet tanks, or rounded twin 45s. This has given me a renewed appreciation for these tanks. If I did the above calculation at 2000 psi (approximately a 10% overfill), I would get almost 104 cubic feet between the two tanks, or twin 50s in a steel 1800 psi tank. I think the next time they go in for hydro, I’ll ask for the “+” stamp on the neck to be renewed.
One of the advantages “vintage” divers had over today’s divers is that we got a better grounding in the science of diving. We even had a book called The New Science of Skin and Scuba Diving1, which triggered a generation of younger divers into the science fields. I think that, to a large degree, this has been lost on modern divers. In this sense, we still have a lot to contribute to the diving community, in that by learning the basics of diving using vintage equipment, they will be stimulated into learning the science behind diving. I’d like others to add some of their stories on this thread about how vintage diving contributed to their understanding of the world around us.
John
1Council for National Co-Operation in Aquatics, The New Science of Skin and Scuba Diving, New Revised Edition, Third Revised Edition, Association Press, New York, Copyrights 1957, 1959, 1962, 1968, 1970 (third revised edition), Library of Congress Catalog card number: 67-14583
Why talk about this with you? Well, my fascination with science, and therefore what I have done professionally, springs from my love of diving in my teenage years. This is what got me into zoology, and into safety. From safety, I became fascinated with how people not only get hurt at work, but how they develop diseases. My first encounter with this was in my diving, where we learned about the direct and indirect effects of pressure on the human body. So now, I’m continuing to learn in chemistry, toxicology, physical hazards (lasers, UV and IR radiation, ionizing radiation, etc.).
Part of this had to do with learning how to compute the amount of chemicals in a room. How does this relate to diving? Well, a while back on a different site, there was talk about reconditioning an old underwater habitat. I had to caution this this was a confined space, and removing paint with chemicals could be hazardous.
But what does this have to do with vintage diving. Well, we learned again about Boyle’s Law, Charles Law, the Ideal Gas Law, and the Combined, or Universal Gas Law. After taking the test, I decided to use these to find out something I had forgotten—the volume of my twin –steel tanks. I had described them as twin 40s, and twin 42s, in various entries at this site. But I really did not know what they were, as the original documentation had been lost. These tanks were sold by Sherwood, I think, as I bought them through a LDS in Roseburg, Oregon with a Sherwood valve. They are stamped “DOT-3AA1800” with the numbers on each tank of “HC263461” and “HC263893.” And then they have their original hydro date of 7/\78 and 8/\78, and I have had them hydroed every 5 years since, including last year. They are unique, in that they have a concave bottom which does not need a tank boot to stand up on its own.
So I decided to use some of the renewed physics skills I have acquired this year to find out the exact volume of these tanks. To do that, I had to fill them with a known quantity of air. I figured that I could calculate this by using one of my single Al 80 tanks, filled at 3000 psi, to determine their exact volume. I wanted to start with a 3000 psi fill on the single Al 80, as that way I would have 80 cubic feet to work with.
To do this, I set my double tank unit up with yolk connector that we use to make doubles out of single tanks. I had to place my set of doubles on a folding table that was unrolled to the correct height, and then had to replace an O-ring on my single 80 before I got the connection right. I used my Trieste II with the Suunto Cobra pressure gauge (accurate to plus or minus 2 psig) on the yolk to make the last connection, and provide the correct psi readings. Here’s what it looked like:
And here’s a top view of the connections. With this setup, I was able to equalize the pressures between the empty twins and the single Al 80.
First, I thought that I could use 3000 psi for the fill, but I had taken the tanks apart for their annual VIP, and put them together again. I started filling them with the 3000 psi tank, only to remember that I had a very slight leak in the manifold. I stopped the fill about 15 seconds into it, bled the set dry, then took my huge crescent wrench and tightened the connecting nuts. Then the tank pressure read 2865 psi. So I needed to make a correction:
80 ft3/3000 psi = X ft3/2865 psi
X = 80 ft3 x 2865 psi / 3000 psi = 76.4 ft3
But in thinking this through, I decided that the 80 cubic foot designation was most probably at what we in the industrial hygiene world call “Normal Temperature-Pressure,” or NTP. NTP in American Standard units is 537 degrees Rankine (77 degrees F + 460 to get the temperature in Rankine units, which in the U.S. Navy Diving Manual, March 1970 is called “Absolute” temperature), and 29.92 inches of water for the air pressure (one atmosphere, if you will). The air pressure doesn’t matter in this calculation, as I am only a few hundred feet above sea level. But I was not working at 77 degrees F, and so I decided to calculate the volume difference at 65 degrees F (my garage temperature). The calculation is:
P1V1/T1 = P2V2/T2, but P1 and P2 are the same, so
V1/T1 = V2/T2, or 76.4 ft3 / (77 + 460) = V2 / (65 + 460)
V2 = 76.4 ft3 x 525 / 535 = 74.69 ft3
So I was starting with 74.69 cubic feet of air in the single Al 80 tank, at 2865 psi. I cracked the valve, and let the two systems equalize. I then let them sit overnight, with the valves turned off (in case of some leaks) to allow them to reach temperature equalization too. Then I read the pressure, and I was surprised. It read 959 psi in both tanks. Excited now about this finding, I ran the following quick calculation:
74.69 ft3 / 2865 psi = X ft3 / 959 psi
X = 74.69 ft3 x 959 psi / 2865 psi
X = 25 ft3
So what had happened is that 74.69 ft3 minus 25 ft3 = 49.69 ft3 transferred to the twin tanks at 959 psi. What is that at its rated 1800 psig rating:
49.69 ft3 / 959 psi = X ft3 / 1800 psi
X = 49.69 ft3 x 1800 psi / 959 psi
X = 93.27 ft3 = 93 ft3
So my small doubles were twin 47 cubic feet tanks, or rounded twin 45s. This has given me a renewed appreciation for these tanks. If I did the above calculation at 2000 psi (approximately a 10% overfill), I would get almost 104 cubic feet between the two tanks, or twin 50s in a steel 1800 psi tank. I think the next time they go in for hydro, I’ll ask for the “+” stamp on the neck to be renewed.
One of the advantages “vintage” divers had over today’s divers is that we got a better grounding in the science of diving. We even had a book called The New Science of Skin and Scuba Diving1, which triggered a generation of younger divers into the science fields. I think that, to a large degree, this has been lost on modern divers. In this sense, we still have a lot to contribute to the diving community, in that by learning the basics of diving using vintage equipment, they will be stimulated into learning the science behind diving. I’d like others to add some of their stories on this thread about how vintage diving contributed to their understanding of the world around us.
John
1Council for National Co-Operation in Aquatics, The New Science of Skin and Scuba Diving, New Revised Edition, Third Revised Edition, Association Press, New York, Copyrights 1957, 1959, 1962, 1968, 1970 (third revised edition), Library of Congress Catalog card number: 67-14583
