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| Questions and answers about the ALOHA hazard modeling software that is part of the CAMEO software suite. |
ALOHA Basics • top
Find out how to download ALOHA, how much it costs, where to go for technical support, how it relates to CAMEO, how to get training, what has changed in the different ALOHA releases, and how to obtain the ALOHA source code.
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Q. How can I get ALOHA?
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A. To get a copy of ALOHA, select the link below. Follow the on-screen instructions to download and install ALOHA.
| Related Links |
| Download ALOHA Download the Windows or Macintosh versions from the Environmental Protection Agency (EPA) CAMEO site. [leaves OR&R site] |
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Q. How much does ALOHA cost?
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| A. ALOHA is free, as are all the programs in the CAMEO software suite.
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Q. Is there technical support for ALOHA?
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A. Yes. If you can't find the answer to your ALOHA question in the manual or the on-screen help, you may want to contact technical support. The CAMEO help desk can be reached via e-mail (CAMEO help desk) or by phone at (301) 429-5018 on weekdays from 8 am to 4:30 pm (EST). The help desk is available to answer questions about any of the programs in the CAMEO software suite. Alternately, you can also e-mail the CAMEO Specialist at the Office of Response and Restoration or contact the EPA CAMEO representative for your region.
| Related Links |
| ALOHA Manual Download the manual from the EPA CAMEO site. Manual includes a guided tour of the program, example problems, and troubleshooting tips. (Document format: PDF, size: 2.1 M) [leaves OR&R site] |
| EPA CAMEO Contacts Find the contact information for the EPA CAMEO representative in your region. [leaves OR&R site] |
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Q. How does ALOHA fit into the CAMEO software suite?
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| A. ALOHA is the hazard modeling program for the CAMEO software suite. (ALOHA models dispersing toxic clouds and estimates fire and explosion hazards.) As part of the suite, ALOHA interacts seamlessly with the CAMEO and MARPLOT companion programs. However, ALOHA can be also be used as a standalone program.
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Q. Where can I get training for ALOHA?
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A. Many instructors across the country offer classes on the CAMEO software suite programs: CAMEO, ALOHA, and MARPLOT. Often ALOHA training is included as part of a larger class on the CAMEO suite, although some instructors may offer ALOHA-specific classes. Follow the link below to find out information about upcoming training classes.
| Related Links |
| CAMEO Training Find out about CAMEO training opportunities and get information for instructors. |
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Q. What changes have been made to ALOHA over the years?
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| A. In February 2007, the current version of ALOHA (v. 5.4.1) was released. To read about significant changes made to each version of ALOHA, follow the link below.
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Q. Can I get a copy of the ALOHA source code?
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| A. Yes, if certain requirements are met. ALOHA contains copyrighted, proprietary data and algorithms obtained from a third party. Our contract prohibits further distribution of this information unless certain requirements are met. E-mail the CAMEO Specialist for more information.
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ALOHA Threat Zones • top
Find out how to display ALOHA threat zones in MARPLOT, ArcView, ArcMap, and Google Earth; why ALOHA limits threat zones length; and why you shouldn't use ALOHA for predictions near the source of the release.
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Q. How do I get MARPLOT to display my ALOHA threat zone?
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A. Completely enter all of your scenario information in ALOHA, and then choose Threat Zone from ALOHA's Display menu. Next, open MARPLOT. Click on the map location where the hazardous chemical is being released. In MARPLOT's Sharing menu, go to the ALOHA submenu and choose Set Source Point. The ALOHA threat zone should now be displayed on your MARPLOT map. Note: You must display the threat zone in ALOHA first, so that ALOHA can make its threat zone predictions and send them to MARPLOT.
| Related Links |
| MARPLOT Overview of MARPLOT, a mapping program with which you can create, view, and modify maps quickly and easily. |
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Q. Can I plot an ALOHA threat zone in a mapping program other than MARPLOT?
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A. Yes. You can use our ArcView extension to plot ALOHA threat zones on maps in ArcView or the ArcMap tool to plot them in ArcMap.
| Related Links |
| ALOHA Arc Tools Download tools that can be used to import an ALOHA threat zone into ArcView 3.x or ArcMap 8.x or 9.x. |
| Related Downloadable Resources |
Communicating with ALOHA If you would like to create your own ALOHA export tool, you may want to read this explanation of how ALOHA passes threat zone information to other programs.
(Document format: PDF , size: 107.2K) |
ALOHA Pass Files This supplement to Communicating with ALOHA deals specifically with sharing threat zone information with other programs; written for developers.
(Document format: PDF , size: 40.0K) |
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Q. How do I get Google Earth to display my ALOHA threat zone?
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A. To display a threat zone on Google Earth, you must first import the threat zone into ArcGIS using the ALOHA Arc Tool extension, and then export it as a KML file (using an extension available on the ESRI site).
| Related Links |
| ALOHA Arc Tools Download tools that can be used to import an ALOHA threat zone into ArcView 3.x or ArcMap 8.x or 9.x. |
| Threat Zones and Other Output Discussion of output from the ALOHA hazard model: threat zone plot, text summary, threat at a point, and source strength. |
| ESRI Visit the ESRI homepage to learn more about their GIS products. [leaves OR&R site] |
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Q. Why won't ALOHA make predictions further than 6 miles (10 kilometers) downwind from a release point?
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| A. There are several reasons we have imposed this limitation in ALOHA. 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 0.6 miles (1 kilometer) of the release point, and in only a few cases were measurements taken as far as 6 miles downwind. 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.
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Q. ALOHA gave me an outdoor concentration estimate that's greater than 1 million parts per million--how can that be?
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| A. 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. (Note that ALOHA will not display toxic threat zones if they are less than 50 meters in length.)
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Chemical Information • top
Find out if ALOHA works with CAMEO Chemicals, why some chemicals aren't included in ALOHA, and why you can't modify some physical property fields.
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Q. Can I use ALOHA with CAMEO Chemicals?
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A. ALOHA cannot interact directly with CAMEO Chemicals, the online version of the CAMEO chemical library and reactivity prediction tool. In the traditional version of CAMEO, you can automatically share information between programs. For example, if you've selected a chemical in CAMEO, you can open ALOHA with that chemical already selected. However, this type of sharing is not currently possible between ALOHA and CAMEO Chemicals--but you can still use CAMEO Chemicals to get more detailed physical property and response information about chemicals you want to model in ALOHA.
| Related Links |
| CAMEO Chemicals Learn about this online version of the most popular parts of CAMEO. Search for chemicals in the CAMEO chemical database, print customized reports with response recommendations, and find out how chemicals would react if they mixed. |
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Q. I just tried to run ALOHA for a sulfuric acid spill, but found that it isn't in the chemical library. It's a really important hazardous substance--why isn't it in ALOHA?
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A. 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. You can see this by checking its properties in CAMEO or online in CAMEO Chemicals. CAMEO reports that the vapor pressure of sulfuric acid is only 1 millimeter at 294.8 degrees F. This is a very low vapor pressure. At the same temperature, water is a gas with a much higher vapor pressure of about 44,000 millimeters. Note: ALOHA's library only includes chemicals from CAMEO that meet ALOHA's standards for air dispersion hazards.
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. When ALOHA models an oleum spill, it only models the dispersion of the sulfur trioxide into the air.
| Related Links |
| CAMEO Chemicals Learn about this online version of the most popular parts of CAMEO. Search for chemicals in the CAMEO chemical database, print customized reports with response recommendations, and find out how chemicals would react if they mixed. |
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Q. Why are some physical property fields grayed out in ALOHA?
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| A. Most of the time, a physical property field is grayed out because the information is from the Design Institute for Physical Properties (DIPPR) of the American Institute of Chemical Engineers. The DIPPR chemical data is proprietary and cannot be viewed or modified. In a few additional cases, physical properties fields will also be grayed out when they can be calculated by the program. When ALOHA estimates properties, you can view the values, but not modify them.
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Miscellaneous • top
Find out how to use ALOHA for a long-duration incident, how accurate ALOHA is, and where to get some other freely available dispersion models.
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Q. I'm responding to a release that began at midday and looks like it will go on for a few more hours. Can you give me some tips on using ALOHA for a long-duration incident?
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A. Here are two key things to keep in mind:- Conditions can change during a long-duration release. For example, the weather can change, and an evaporating puddle can change in area or temperature. This is one of the reasons that ALOHA limits its predictions to one hour. Whenever conditions change substantially, discard your out-of-date ALOHA output, revise the inputs that have changed, and re-run ALOHA.
- If you expect that a release may continue into the night, be aware that the hazard from an air release is typically worst late at night and in the very early morning when the atmosphere is most stable. (The more stable the atmosphere, the farther a chemical cloud can travel before it is diluted below hazardous concentrations.) Try running ALOHA for the predicted nighttime weather conditions. For best results, ask the National Weather Service for their predictions of nighttime weather conditions. If you cannot contact a meteorologist, try running ALOHA using a low wind speed and high stability class (E and F are the most stable classes; click Override to override ALOHA's stability class choice, if necessary).
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Q. How accurate is ALOHA?
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A. 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 200 parts per million (ppm) and no less than 50 ppm, if the real concentration at that location was 100 ppm.
To the best of our knowledge, ALOHA meets this definition of accuracy. 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.
Other factors affect ALOHA's ability to make accurate predictions for any particular release:- The real world is enormously complex, and many events happen randomly. This complexity and randomness can't be completely captured in any computer program.
- Because ALOHA makes simplifying assumptions about the circumstances of a release, its predictions are likely to be more accurate when those assumptions are met than when they are not. For example, ALOHA assumes that the terrain below a dispersing gas cloud is flat and free of obstacles. Because it makes this assumption, it is likely to make more accurate predictions for a release in relatively flat, open country than for a release in the downtown section of a major city, or in mountainous terrain.
- ALOHA's predictions can be less accurate, or even wrong, when the model is used incorrectly.
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Q. What other models are available for dispersion modeling?
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A. Two sites offer dispersion models for free downloading:
1. The Support Center for Regulatory Air Models site offers many dispersion models, along with user guides and guidance documents. The site is maintained by the Environmental Protection Agency's Air Quality Modeling Group and the site focuses primarily on air quality modeling rather than accidental release modeling. However, TSCREEN, SLAB, and DEGADIS are available from this site; all are useful for modeling accidental releases. TSCREEN is the easiest of these to use, and comes with an extensive user guide/workbook; it does both heavy gas and Gaussian modeling and handles both instantaneous and continuous releases.
2. Lakes Environmental Software offers TSCREEN, SLAB, DEGADIS, user guides, a variety of air quality models (including a fugitive dust model), and guidance documents for free downloading.
| Related Links |
| Support Center for Regulatory Air Models This site, maintained by EPA's Air Quality Modeling Group, offers many dispersion models, along with user guides and guidance documents. [leaves OR&R site] |
| Lakes Environmental Software Download free air dispersion models and guidance documents. This site is maintained by Lakes Environmental Consultants, Inc. [leaves OR&R site] |
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Portable Weather Stations • top
Find out about common SAM transmission errors in ALOHA and who makes ALOHA-compatible weather stations.
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Q. I am using a Station for Atmospheric Measurement (SAM) with ALOHA. 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?
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A. Either the SAM has not yet been collecting data for 5 minutes, or ALOHA has not received valid data. Check the Text Summary window for a message alerting you to the specific problem with the SAM. 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 1200. For more information about setting up a SAM for ALOHA, select the link below.
| Related Downloadable Resources |
Designing an ALOHA Met Station Learn how to design a portable meteorological station to work with ALOHA.
(Document format: PDF , size: 37.8K) |
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Q. What companies make ALOHA-compatible weather stations?
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A. We are aware of several vendors who advertise that their portable meteorological stations have been configured to work with ALOHA. Select the link below to go to the list of vendors.
| Related Links |
| Met Station Vendor List Look through a list of vendors of portable meteorological stations designed to work with ALOHA and find out how to design a met station for ALOHA. |
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Source Strength • top
Find out how ALOHA uses exponential notation and why you may need to re-enter source information after changing atmospheric conditions.
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Q. In the Text Summary, I see tank volume estimated to be 5.2e+008 gallons. How many gallons is that?
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| A. A lot! ALOHA displays its results in an abbreviated form (exponential notation) whenever numbers are too large to display normally. Exponential notation is a way of displaying a number as a digital number multiplied by a power of 10. For example, 5e+003 is interpreted as the digital number 5 multiplied by the quantity 10 taken to the power of 3. Numerically, this would be 5 x (10 x 10 x 10), which is equal to 5,000. So, 5.2e+008 is 5.2 x (10 x 10 x 10 x 10 x 10 x 10 x 10 x 10), which is equal to 520,000,000 gallons.
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Q. When I changed some atmospheric conditions, ALOHA told me that it is unable to verify the consistency between my new atmospheric data and the source data. Then I had to reset the source. Why?
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| A. ALOHA's Puddle, Tank, and Gas Pipeline source strength calculations are affected by atmospheric conditions. If you modify those atmospheric conditions, ALOHA recomputes source strength whenever it can. In some cases it cannot, so it asks you to reenter information about the source. For example, by increasing air temperature, you may cause a tank to be filled to more than 100 percent of capacity, or a puddle's temperature to increase above its boiling point. In such cases, you must enter new source information to resolve the problem.
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