Q. How do I get MARPLOT to display my ALOHA threat zone?

A. You must display the threat zone in ALOHA first, so that ALOHA can make its threat zone predictions and send them to MARPLOT (a mapping program).

1. Completely enter all of your scenario information in ALOHA, and then choose "Threat Zone" from ALOHA's Display menu.
2. Open MARPLOT and click on the map location where the hazardous chemical is being released.
3. In MARPLOT, click on the ALOHA icon in the toolbar and then select the Set Source Point at Click Point option. The ALOHA threat zone should now be displayed on your MARPLOT map.

Q. Can I plot an ALOHA threat zone in a mapping program other than MARPLOT?

A. Yes. You can use our MARPLOT mapping program as a way to export ALOHA threat zones in several output formats, including the SHP file format used in Esri's ArcGIS products and KMZ file format used in Google's mapping products. Starting with ALOHA 5.4.2, you can also export threat zones as .KML files for use in Google Maps and Google Earth. In addition, the ALOHA Technical Resources page has information about how ALOHA shares data with other software applications.

Q. How do I get Google Maps or Google Earth to display my ALOHA threat zone?

A. Use the "Export to KML" feature in the latest version of ALOHA. Note that you will need to type in a value for the latitude and longitude of the source location. The KML file will include information about the threat zone (such as Levels of Concern).

Q. When I try to display an ALOHA threat zone in MARPLOT, I see this message: “Programmer error message: Err: -1. Did not write to file C:\Program Files (x86)\ALOHA\ALHAIMP2.mie because of error.” How can I fix this?

A. This error is due to a permissions issue, but it has been resolved since ALOHA 5.4.4. If you see this error, we recommend that you upgrade to the latest version of ALOHA. If that is not possible, then you can resolve the issue by adjusting your permissions. In older versions of ALOHA, you must have write permissions in the ALOHA folder to write out the .mie file that MARPLOT needs to display the ALOHA threat zone. Verify your permissions for the ALOHA folder and correct them if needed. You may need to contact your IT Systems Administrator to change the permissions.

Q. Why won't ALOHA make predictions further than 6 miles (10 kilometers) downwind from a release point?

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. Read more about the limitations and constraints of the ALOHA model.

Q. ALOHA gave me an outdoor concentration estimate that's greater than 1 million parts per million—how can that be?

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.)

Q. Can I use ALOHA with CAMEO Chemicals?

A. You can share information between ALOHA and the CAMEO Chemicals desktop format (but not with the other CAMEO Chemicals formats). For example, if you're looking at a chemical datasheet in CAMEO Chemicals 2.8.0 or later, you can use the 'Select in ALOHA' button at the top of the datasheet to open ALOHA with that chemical already selected. This button is only shown for chemicals that may be selectable in ALOHA. (In older versions of CAMEO Chemicals, this function is available in the Sharing menu instead.)

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?

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 Chemicals. CAMEO Chemicals reports that the vapor pressure of sulfuric acid is only 1 millimeter of mercury 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 of mercury. Note: ALOHA's library only includes chemicals from CAMEO Chemicals 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.

Q. Why are some physical property fields grayed out in ALOHA?

A. Most of the time, a physical property field is grayed out because the information is from the American Institute of Chemical Engineers' Design Institute for Physical Properties (DIPPR). 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.

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?

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).

Q. How accurate is ALOHA?

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.

Read more about the limitations and constraints of the ALOHA model.

Q. What is the difference between ALOHA and the RMP*Comp software?

A. You can use either ALOHA or the RMP*Comp software to complete the hazard analyses required under the Risk Management Planning (RMP) rule. RMP*Comp is a simple tool that steps you through a short list of questions about the regulated substance (such as the amount released) and implements the procedures exactly as specified in the RMP guidance. ALOHA is a more complex tool that can also be used for emergency response and planning activities beyond RMP planning. For more information on the difference between these programs, read the Ask Dr. ALOHA article on using CAMEO tools for RMP and EPCRA hazard analyses.

Q. What other models are available for dispersion modeling?

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.
2. Lakes Environmental Software offers a variety of air quality models. This site is maintained by Lakes Environmental Consultants, Inc.

Q. Why are some menu items grayed out?

A. ALOHA's menus are set up so that you typically move left-to-right through ALOHA's SiteData, SetUp, Display, and Sharing menus as you enter information about a scenario. 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.

Q. What is an .alo file? How do I create an .alo file?

A. An .alo file is a saved copy of an ALOHA scenario. This type of file may also be referred to as an ALOHA save file. When you open an .alo save file in ALOHA, it will use information from the save file to fill in details (such as location or weather) for a particular scenario. If you are using the .alo file for planning, this will allow you to re-run the same scenario again later without having to re-enter all of the data. If you are using the .alo file for an emergency response, you can use the .alo file to quickly pre-load a scenario with a chosen location, tank size, etc.—but, in this case, you'll need to do some additional data entry to provide updated release details (such as current weather or the hole size in a tank). To create an .alo file, enter all of your data for a scenario into ALOHA, and then select Save from the File menu.

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?

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. Find out more information about setting up a SAM for ALOHA.

Q. What companies make ALOHA-compatible weather stations?

A. We are aware of several vendors who advertise that their portable meteorological stations have been configured to work with ALOHA. Look through a list of vendors of portable meteorological stations designed to work with ALOHA.

Q. In the Text Summary, I see tank volume estimated to be 5.2e+008 gallons. How many gallons is that?

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.

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?

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.  

Even more questions, comments, or suggestions? Contact us.