Ammonia Inventory Calculations - The maximum inventory is the maximum amount of ammonia that will ever be present in your system based on filling everything to capacity. Maximum Intended Inventory is the amount you will never exceed in your system as documented in your PSI. The maximum intended inventory takes into account engineering and administrative controls and is, therefore, less than the absolute maximum your system can hold, but normally more than the actual charge.


In this case, administrative controls are simply your policies relating to the maximum amount you will maintain in vessels, etc during normal operations.


Where is Maximum Intended Inventory Required?


Process Safety Information Report
EPA RMP Submit 1.17
Hazard Assessment Worst Case Release
EPA Tier II Submittal

Department of Homeland Security Top Screen Survey


PROTEXUS will walk down P&IDs and gather all information necessary for ammonia inventory calculations. This includes documentation of equipment, pipe lengths, size, and service.



Piping and Instrumentation Diagrams P&IDs are critical because they depict the connectivity of equipment and the instrumentation used to control the equipment.

  • Provides a visual reference to equipment configuration, valving, sensors, etc.

  • Provides useful information to assist in analyzing process hazards.

  • Supports development of operating procedures.

  • Communicates the configuration of equipment clearly and concisely to improve operator understanding of the process and reduce human errors.

  • Records the current (as-built) state of the process so that changes can be planned safely and effectively.

Unfortunately, many facilities have P&IDs that lack critical elements, or do not represent the current operating configuration and system components. These errors cause operating errors, delay efforts to minimize an ammonia release, and further increase the risks to emergency responders.

PROTEXUS will properly document P&IDs (redline existing P&IDs, create new drawings, etc.), electronically update/create the P&IDs in AutoCAD, and submit to the facility completed “record copy” P&IDs in hard copy and electronic (AutoCAD) format, as they are completed by PROTEXUS.




Ammonia Refrigeration Ventilation Calculations - According to 29 CFR 1910.119(d)(3)(i)(E), employers who are covered under the PSM rule that use ventilation systems, as part of their PSM programs, must compile written process safety information pertaining to that equipment, including the design basis. Section 1910.119(d)(3)(i)(F) requires employers to document design codes or standards employed when compiling such written process safety information. (The documentation must also include all assumptions and calculations.)


Therefore, industry standards such as those published by NFPA and IIAR, including NFPA 30, NFPA 58, and IIAR Bulletin 111, could serve as examples of design basis for ventilation systems, when those are designated and employed; and the documentation containing such information will meet 1910.119(d)(3)(i)(E) requirements. Such information pertaining to the equipment in the process must also include electrical classification under 1910.119(d)(3)(i)(C) and safety systems (e.g., interlocks, detection or suppression systems) under 1910.119(d)(3)(i)(H).




Ammonia Refrigeration Relief Vent Calculations - Relief valves are an important safety feature in industrial ammonia refrigeration systems. They protect the system from overpressurization and possible explosion. The discharge piping is also an important part of the relief valve system, which must be sized properly so the relief valve capacity is not affected and it must route the ammonia to a safe discharge location.

When designing relief valve systems it is important to follow the proper codes and standards as well as understand the relationships between all components. Selecting the relief valve is straightforward based on the requirements of the vessel. It is not wise to greatly oversize the relief valve because the discharge piping is sized based on the selected relief valve and the required pipe routing.


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