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On Board the OSV BOLD: Experimenting Under Pressure…Puerto Rico Highlights Continued

2009 March 8
For more than a month, EPA’s Ocean Survey Vessel (OSV) Bold is studying the health of the waters around Puerto Rico and the U.S. Virgin Islands. EPA scientists and non-scientists will blog about their research and what it’s like to live and work at sea.

About the author: Mark Reiss is a marine environmental scientist with the dredging, sediments and oceans team in EPA Region 2, comprising New Jersey, New York, Puerto Rico and the U.S. Virgin Islands. He is one of the principal investigators on the OSV BOLD’s Puerto Rico voyage.

As I had talked about in yesterday’s post, we wanted to have a little fun after all the hard work the crew and science members had put in to complete our surveys. So, we decided to see what would happen if we securely attached foam cups, signed by students from three science classes at a Manhattan middle school and by three teachers from Puerto Rico that joined us on the OSV BOLD, and drop them down on the CTD to 2,500 meters. The weight of all that water produces incredible pressure, just over 3,600 pounds per square inch (PSI). Our instruments are built to withstand this pressure, but foam coffee cups aren’t. The pressure causes the cups to shrink to miniature versions of themselves, as it forces the air in the foam out and sticks the plastic together.

 image of styrofoam cups, soda can, an egg, and an orange on a table
Various items prior to being sent into the depths of the sea.

The crew had seen that before on other cruises so they knew what would happen to the cup. But this time we also sent down an uncooked egg, an unopened can of soda, an orange, a waffle, and a few floating key chains—basically anything that wasn’t tied down! Everyone on the boat made predictions about what would happen to the items, and they were hotly debated for the three hours it took to make the cast. We all gathered on deck waiting to see what happened.

I got mostly firm predictions about what would happen to the soda and the egg we sent down when I polled the boat and scientific crew (though a few people admitted that they just were guessing). And I got a lot of good theories to back those predictions up.

image of crushed styrofoam cups, soda can, an egg, and an orange on a table
Various items after exposure to the incredible pressure of the sea.

Some confidently predicted that that the egg and soda can would be “toast.” Some people thought that only one would make it or that the egg would break if it went down lying on its side, but would be okay if it went down on its end. Some said that the items would explode. The best one came from our captain who pointed out that the shell of the egg is an engineering marvel of nature so it would withstand the pressure, but the soda can has a weak spot built in and that would make it explode.

Well, maybe the captain did predict the egg would come back fine, but then why did the soda can make it okay, too?

An egg shell is indeed a natural engineering masterpiece, but that’s not why it survived. The reason the soda can, egg and orange did not crush is pretty simple. (By the way, things do not explode under pressure). They are mostly filled with fluid, and fluids do not compress or squeeze together like air does. The fluid inside pushed against the can and the shell from the inside and kept them from collapsing while the pressure outside tried to crush it. If the egg were hollow, even the engineering properties of its shell would not have saved it. The results of our little experiment definitely surprised most of us.

Editor's Note: The opinions expressed here are those of the author. They do not reflect EPA policy, endorsement, or action, and EPA does not verify the accuracy or science of the contents of the blog.

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