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RMP*Comp Frequent Questions


I've noticed that for certain chemicals, RMP*Comp gives substantially different distances to the toxic endpoint than previous versions. Why?

In the current version of RMP*Comp, we have incorporated new chemical-specific distance tables for ammonia, chlorine, and sulfur dioxide. The generic tables are still used for other chemicals (you can see the generic tables in the Offsite Consequence Analysis Guidance (OCA Guidance).

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I've noticed that for certain chemicals, RMP*Comp gives substantially different distances to the toxic endpoint than I get when I make calculations by hand, following the Off-Site Consequence Analysis (OCA) Guidance procedures. Why the differences?

RMP*Comp was revised in accordance with changes to the OCA Guidance which have not yet been made public. EPA generated chemical-specific distance tables for chlorine, ammonia and sulfur dioxide, and incorporated these tables into the latest, not-yet-public version of the OCA Guidance, which should shortly be made public.

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I tried running the same scenarios in ALOHA and in RMP*Comp. I got different answers. Why?

The results you obtain using RMP*Comp may not closely match the results you obtain running the same release scenario in a more sophisticated air dispersion model such as ALOHA or DEGADIS. That's because of a fundamental difference in purpose between those models and RMP*Comp. RMP*Comp is a planning tool, designed to help you to easily identify high-priority hazards at your facility. It makes simple, generalized calculations. In contrast, models like ALOHA and DEGADIS are intended to give you as accurate an estimate as possible of the extent and location of the area that might be placed at risk by a particular chemical release. They account for many more of the factors that influence the dispersion of a hazardous chemical. (For this reason, when you need to make decisions during an actual response, use models like ALOHA or DEGADIS, not RMP*Comp.)

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Can I use RMP*Comp for emergency response?

No. It's a planning tool. Many other tools are available for response, including ALOHA and the Chemical Reactivity Worksheet (the Worksheet can be downloaded for free from this site). You can learn more by reading What's in the RMP Toolbox?

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Will RMP*Comp be updated? If so, would I have to redo calculations I might already have made with an earlier version?

No, you do not have to redo your work if you have already completed your consequence analyses. RMP*Comp is based on the EPA's Offsite Consequence Analysis Guidance (OCA Guidance), which is an "evergreen" rather than a final document; it can be updated as new information or better modeling techniques become available. 1) You are not required to redo your consequence analyses every time there is a change to the Guidance. 2) However, as you develop your analyses, be sure to use either the latest version of RMP*Comp or the latest edition of the Guidance. As changes are made to the Guidance, we'll update RMP*Comp.  The changes will automatically be available in both the browser-based version, and in the downloaded version.  (When the downloaded program starts, it checks for, and applies, any updates.)

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For alternate release scenarios, RMP*Comp uses set values for meteorological conditions like humidity, wind speed, temperature, stability class, and so on. Is there a way to change those values? I want to use meteorology data from my own location.

RMP*Comp indeed uses fixed values for certain atmospheric parameters, and does not allow them to be set by the user. This is because the software is intended as a simplified model, adhering to the EPA's Offsite Consequence Analysis Guidance (OCA Guidance), that is acceptable for compliance with the Risk Management Program (RMP) Rule. Other tools/models may also be used. In order to use local meterological data, you'd have to use one of those other tools.

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Does RMP*Comp perform some math or modelling in order to arrive at an endpoint distance, or is it simply interpolating from the tables in the EPA's Offsite Consequence Analysis Guidance (OCA Guidance)?

RMP*Comp follows the procedures set out in the OCA Guidance. This means that for some scenarios, the endpoint distance is arrived at via table lookups, for others via calculations. (An example of the latter is the case of pool fires; see Section 12.2 of the Guidance.) However, when table lookups are used, no interpolation is performed (see Section 4.0 of the Guidance).

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