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Ask Dr. ALOHA: Working with Toxic and Odor Thresholds, Step 1

Entering Scenario Information into ALOHA (Fictional Example)

Jim starts ALOHA and begins to enter information about the spill scenario. To assess the hazard to Oceanside City, he assumes that the vessel—still leaking ethyl mercaptan—has docked at the port (which is adjacent to the main business district). He calls the NOAA National Weather Service to obtain information about the expected weather conditions for the vessel's estimated arrival time and location. He is especially concerned to hear that the prevailing wind would blow the ethyl mercaptan vapors from the dock directly into the city. He enters these weather conditions into ALOHA. However, Jim knows that if the vessel does end up docking in port, he'll need to get updated weather information and re-run the scenario.

The vessel captain told him that crew members observed a small pool of ethyl mercaptan liquid on the ship's deck. They estimated the pool to be shallow and about 2 feet by 2 feet in area. From ALOHA's SetUp menu, Jim chooses the "Puddle source" option, and enters information about the puddle, guesstimating that it's about half an inch deep and at ambient temperature. He'll revise these entries and run ALOHA again if more information about the puddle becomes available. Given that the ethyl mercaptan is still leaking, Jim will make a point of checking back with the vessel captain from time to time to learn whether the pool has expanded in area.

When Jim has finished entering information about the scenario, his Text Summary screen looks like the one below.

ALOHA estimates that about 8.8 pounds of ethyl mercaptan would evaporate in 24 minutes.

Now Jim is ready to display the threat zone estimate in ALOHA (step 2).

Last updated Monday, February 8, 2016 4:30pm PST