RAST Software Issues
Q: I get errors when I load equipment information from the equipment table. What is wrong?
A: The errors you may be getting for loading equipment information from the equipment table is the result of a decimal being entered as “,” rather than “.”. We have recommended that in using RAST the “.” be used for decimals as some of the excel macros may not recognize “,”. This has been an issue we have tried (unsuccessfully) to address. To best to set the decimal notation as “.” in Excel for RAST use.
Chemical Property Issues
Q: What if our chemicals do not have ERPG values?
A: If you are fortunate enough to have toxicologists or industrial hygienists at your company consult with them about appropriate values. You can also use AEGL values or PAC values. The PAC database contains roughly 20 times the number of chemicals as the ERPG database.
PAC values are defined similar to AEGL and ERPG as:
- PAC-1: the (one hour exposure) concentration above which it is predicted that the general population, including susceptible individuals, could experience mild, transient health effects
- PAC-2: the (one hour exposure) concentration above which it is predicted that the general population, including susceptible individuals, could experience irreversible or other serious health effects that could impair the ability to take protective action.
- PAC-3: the (one hour exposure) concentration above which it is predicted that the general population, including susceptible individuals, could experience life-threatening health effects.
The PAC database can be found at:
Technical Clarification Notes
Q: What would you recommend the operating temperature be set as for a heat exchanger – e.g. the average, the inlet or the outlet temperature?
A: The Process side of a Heat Exchanger is the Operating Temperature. For the Heating Media side, I typically use the source temperature (inlet) as this is the highest temperature we would expect.
Q: When working with a compressor, it is difficult to define an exact volume and MAWP (assumed to be the max outlet pressure of the compressor) due to their nature, so I am assuming a suitable estimate would be satisfactory for the model to predict potential major accidents.
A: RAST is a screening tool and not sophisticated to truly “model” the operation of a compressor or other equipment. We suggest that you use volume as that of the equipment and connected piping to the first valve as this is what would leak out when blocked in.
Chemical Hazards Engineering Fundamentals (CHEF) Q&A
Questions: Please contact Bruce Vaughen at brucv@aiche.org with questions, comments, or suggestions about our FAQs content.