Aloha modelling software

The primary reason for this cutoff is related to the equations ALOHA uses to predict threat zone length. These equations came from a series of field experiments in which gases were released and tracked as they traveled downwind. In those experiments, nearly all the measurements were taken within 0. This means that we can't be sure that the dispersion estimation methods used by ALOHA and other air models would be accurate farther from the source.

Also, over longer distances effects such as terrain steering can significantly affect the threat zone, and ALOHA does not include such effects in its prediction. ALOHA gave me an outdoor concentration estimate that's greater than 1 million parts per million—how can that be? You may have asked for a concentration estimate for a point very close to the source.

Concentrations of a pollutant are extremely high right at the point of release and drop off as you move downwind. The equations we use in ALOHA were developed to give answers for the relatively lower concentrations that occur a bit farther from the source. These equations assume the concentration is infinite at the source. Rest assured that the unrealistic concentrations very near the source do not affect the answers for the rest of the threat zone.

We recommend that you avoid using ALOHA to estimate concentrations at locations very close to the source. By ALOHA's standards, sulfuric acid is not volatile enough to be considered an outdoor air dispersion hazard, even though it is hazardous when inhaled.

That is, under normal conditions, it cannot enter the atmosphere fast enough to reach concentrations hazardous to people within a large area. This is a very low vapor pressure. At the same temperature, water is a gas with a much higher vapor pressure of about 44, millimeters. ALOHA's library primarily includes pure chemicals; however, there are a few solutions and one mixture.

The mixture is oleum, which is a combination of sulfuric acid and sulfur trioxide. Oleum is also known as fuming sulfuric acid. However, you should not use this mixture to try to model a sulfuric acid spill. Oleum is included in ALOHA's library because sulfur trioxide is considered to be an air dispersion hazard. In a few additional cases, physical properties fields will also be grayed out when they can be calculated by the program. I'm responding to a release that began at midday and looks like it will go on for a few more hours.

At least one expert in atmospheric dispersion modeling has stated a rule of thumb: a model is considered accurate if its estimates fall within a factor of two of what would happen in a real release. This rule is based mainly on expert judgment, rather than experimental evidence. By this rule, a model would be accurate if, for example, it predicted that the concentration of a dispersing gas at a particular location would be no more than parts per million ppm and no less than 50 ppm, if the real concentration at that location was ppm.

But it's important to recognize that our ability to judge the accuracy of dispersion models is limited by data scarcity: Because only a few field experiments have been conducted in which hazardous gases were released and their concentrations measured, we have few data to measure our models against.

For more information on the difference between these programs, read the Ask Dr. If you haven't completed all of the necessary information in an earlier step, you will find that menu items remain grayed out in the menus further to the right. For example, you must enter the location for the release before you can enter the weather information. When you open an.

If you are using the. To create an. I have set the SAM options using the Atmospheric menu, but the Source menu is not available it appears gray —so I can't set my source. What's the problem? One cause of invalid data can be an incorrectly set baud rate. If your SAM station can be set to different baud rates, make sure the baud rate is set to We are aware of several vendors who advertise that their portable meteorological stations have been configured to work with ALOHA.

In the Text Summary, I see tank volume estimated to be 5. How many gallons is that? A lot! The Macintosh version can be run on Mountain Lion Operating systems not listed here have not been tested and are not supported.

This will replace the old application with the new one, while still maintaining all of your settings. Any chemical information that you have added to the chemical library will not be saved and you will need to re-enter that information.

ALOHA's help topics include an example problem that you can work through to familiarize yourself with the program. Skip to main content. Contact Us.