The packages arrive midmorning at a small laboratory in southeastern Connecticut.
The cardboard boxes are carefully, tightly packed with 4-ounce jars. Inside those glass containers is a black goo that occasionally has stirred panic in some Florida coastal communities.
Is it from the Deepwater Horizon wellhead? Was it moved along by the powerful loop current in the Gulf of Mexico? Will it doom tourism in a coastal town?
This scenario has occurred hundreds of times since the April 20 disaster in the gulf. At the first sign of tar balls, oil sheen or a potential threat of oil off Florida or other Gulf Coast states, pollution investigators send samples to the U.S. Coast Guard's Marine Safety Laboratory in New London, Conn.
Military chemists conduct daily tests to determine who, if anyone, might be at risk.
Back home, locals anxiously await the results. A few weeks ago it was Cocoa Beach. Before that it was Miami and Key West.
"We're at more than five times our normal workload,'' said Wayne Gronlund, a chemist who runs the lab. "It's been fairly intense.''
So far, most of Florida has been lucky.
"I think,'' Gronlund said, ''we're all expecting it to change.''
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Nine times out of 10, these samples come from the gulf. About half of them come from the Florida coast, where residents are especially wary of BP oil tarnishing their shores.
So far, no matches have been made south of the Panhandle.
"The harsh reality is that there's usually tar balls in Florida," Gronlund said. "They're just not as big a deal most of the time."
The first shipment of suspicious Florida oil arrived at the lab May 18. Tar balls dotted the beaches of the Keys, prompting headlines and fears that oil had entered the loop current and made its way south.
"The Coast Guard flew them up here in a hurry," Gronlund said.
The origin of those tar balls turned out to be a heavy fuel oil, not even close to the makeup of fresh crude. Actually, Gronlund said, most of the tar balls found on Florida's east and west coasts since May have been from heavy fuel sources.
It doesn't take an oil disaster to produce tar balls. They also form from natural seeps or sunken ships or other sources.
It ultimately falls to the Coast Guard lab to determine whether the oil is from the BP wellhead or some other source.
The lab employs 10 people: two chemists, six technicians and two administrative workers.
It can take anywhere from a few hours to a few days to determine if the sample matches the BP crude.
It took about a week to quell recent fears that BP's disaster was the cause for 80 pounds of beached oil in Cocoa Beach.
The lab makes no attempt to determine the source.
"We're the crime lab," Gronlund said. "We're not the investigators."
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It's a complex process.
First, technicians reduce the glob to its purest form, extracting water, seaweed and sand.
That readies the oil for its first test. It enters a machine that separates components by their boiling points.
Chemists then examine the components to see if any match the makeup of BP's crude.
If it's obviously not a match, they can file a report within four or five hours.
But if uncertain, chemists move to a second phase, known as molecular fingerprinting.
In a complex testing process than often takes several hours, a machine looks for molecules that existed at the time the oil glob was formed. Petroleum formed in varying conditions can exhibit clear chemical differences.
A series of complex graphics further break down the molecules and reveal any fundamental differences between the sample and BP crude.
At that point, there are no doubts. It's a match or it's not.
The little lab in Connecticut decides, and another beach learns its fate.
In Cocoa Beach, it was relief.
"We were very glad to know that the oil didn't come from the gulf,'' said Jerry Stansfield, the city's public information officer. "But that could change. You don't know what going to happen. We're watching and we're preparing.''