[This blog series derives from a technical paper written by Eli Macha, President of Macha PSM]
Within 14 major program elements, Process Safety Information (PSI) has 14 sub-elements of its own. These 14 PSI sub-elements fit into three categories: information pertaining to the hazards of the highly hazardous chemicals in the process, information pertaining to the technology of the process, and information pertaining to the equipment in the process.
The 14 PSI sub-elements can be essentially broken down as follows:
Hazards
1: Safety Data Sheet
Technology
2. Block Flow or Process Flow Diagram
3. Process Chemistry
4. Maximum Intended Inventory
5. Safe Upper and Lower Limits
6. Consequences of Deviation
Equipment
7. Materials of Construction
8. Piping and Instrumentation Diagrams (P&IDs)
9. Electrical Classification
10. Relief System Design and Design Basis
11. Ventilation System Design
12. Design Codes and Standards Employed
13. Material and Energy Balances
14. Safety Systems
The scope of this blog series is too broad to provide commentary on each PSI sub-element—not to mention many contractors, consultants, and end-users differ on their preferred methods of satisfying these requirements.
Instead, three PSI pointers will be added to the “to-do” list.
First, if an end user takes over a PSM program and there is no PSI to speak of, the first thing to do is have detailed P&IDs developed. Peter Thomas, P.E., President of Resource Compliance, has said, “P&IDs are the cornerstone of process safety information.” Thomas’ point is helpful for those without any PSI. If you have detailed P&IDs, many other PSI elements can be developed from them. Similarly, if the facility has P&IDs, but they are outdated, missing important data, or otherwise in disarray—prioritize updating them or developing new drawings.
Second, this one seems simple, but if some PSI has been developed, but not all PSI sub-elements, prioritize developing records for each sub-element. Numerous compliance audits have resulted in recommendations for not having documents on file for process chemistry or materials of construction. Depending on how thorough they are, each of these records can be satisfied with a 1 to 2-page document. Regulators will often have an inspection checklist with each of these PSI sub-elements on it—if the facility simply has a document with a title matching the requirement, this will avoid unnecessary findings.
Third, if all PSI is already on file, the facility is in better shape than many PSM programs. Instead of simply checking the box and moving on, investigate to determine if the PSI is current. If past management of changes are on file, these can be a helpful tool to cross-check whether the PSI has been updated accordingly.
Here are some questions to ask:
· Do the block flow diagram and P&ID match the physical equipment installed?
· Does the PRV list (if there is one) reflect accurate installation dates which are within five (5) years?
· Does the Design Codes and Standards Employed document reflect the actual standards used to design the system?
Next, what are some common pitfalls for ammonia refrigeration process safety information programs? Apart from missing or inaccurate P&IDs, the most common issue lies with the maximum intended inventory. This calculation can and should take administrative controls into account. No sane operator would ever intend to fill the system with as much ammonia as it could possibly hold—this is not how ammonia refrigeration systems are designed to operate.
For instance, pressure vessels should not exceed a liquid level of 85% (or 80% if a facility is being conservative) to avoid a BLEVE (boiling liquid expanding vapor explosion). Beyond avoiding a BLEVE, many vessels operate at much lower liquid levels. Similarly, evaporators and other components are usually designed to operate while being only partially filled with liquid. With this being the case, the difference between the maximum intended inventory and the maximum possible inventory is always a wide margin. The amount that can possibly fit into a system can be as much as 2-3 times that of what ought to be in the system for proper operation.
The first mistake to avoid when calculating the maximum intended inventory is to avoid calculating the maximum possible inventory—in other words, the calculation should be based on the maximum amount of ammonia intended to be charged into the system to maintain proper operation.
If the low-hanging fruit has already been addressed, and the common pitfalls have been avoided, here is one pointer for leveling up a facility’s PSI program:
Develop a comprehensive analysis for the entire relief vent system.
Many documents and calculations intended to satisfy the relief system design and design basis requirement only calculate that pressure relief valves have sufficient capacity for the component they are protecting. In the EPA’s “Ammonia Refrigeration List of Key Safety Measures,” the following requirement is listed under Machinery Room and System Design, “Documentation exists to show that pressure relief valves that have a common discharge header have adequately sized piping to prevent excessive back pressure on relief valves, or if built before 2000, have adequate diameter based on the sum of the relief valve cross-sectional areas.” This particular requirement had been so neglected by regulators and the industry as a whole that many end users believe properly sizing the relief vent piping is a new requirement.
On the contrary, the same design equations have been in IIAR 2 for decades—even though many systems designed prior to circa 2015 have improperly sized relief vent branches and headers. While these calculations can be completed with other programs or spreadsheets, the most comprehensive medium for this task is the Industrial Refrigeration Consortium’s Relief Vent Tool Version 2.0 (sometimes referred to as the IRC Tool). This tool enables the user to create a visual diagram of the relief system, to enter pipe and elbow sizes, to account for varying termination points, and to calculate for different scenarios (e.g., a fire on one side of the machinery room). Once PSI has been optimized, the PSM Coordinator must also look to the process hazard analysis.
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