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By Gary D. Nichols, PE
In the previous article in this series, "Process Analyzer System Safety and Ergonomics, Part I," we began our discussion of analyzer system safety and ergonomics by describing a “typical” refinery or petrochemical plant analyzer shelter with an assortment of gas chromatographs, single stream analyzers and associated utilities and infrastructure. The discussion proceeded to analyzer shelter gas monitoring, safety shutdown systems, and other safety and ergonomic features needed to protect personnel working on, in, and around the analyzer shelter. This article continues that discussion by addressing the safety and ergonomics of analyzer sample handling systems (SHS), constructability and construction safety, and operations and maintenance.
Sample Handling Systems
Analyzer sample handling systems have special needs for safety and ergonomics. Because the SHS usually includes the analyzer fast loop and sample return, it is best to place the SHS on the outside of the analyzer shelter and as close as possible to its corresponding analyzer inside the shelter. The measure loop, generally of much lower volume flow than the fast loop, takes off from the fast loop, into the shelter and analyzer, and returns to the fast loop or a sample disposal system to minimize the amount of sample entering the shelter.
Some photometric analyzers incorporate fiber optics into the measurement optics in order to separate the sample cell from the rest of the photometer. This design feature permits eliminating the SHS entirely by facilitating measurement in the process line, or reducing SHS complexity so the sample does not need to be brought into the analyzer shelter.
Injuries and inefficiencies from the improper physical layout of SHS and other analyzer system devices are preventable. Injuries include burns and scrapes to the hands from intricate work in close spaces and electrical shocks from unguarded terminals. Inefficiencies result from poor design, such as inappropriate spacing between devices which either must or must not be operated simultaneously.
Other errors are including features that require two technicians to take apart major assemblies to service one frequently accessed device, when a better design would require only one (unless it is a hazardous task that requires two or more for safety) or a design that requires a mirror to view one device while working on another. Most of these problems are avoidable if a layout review is required as part of the drawing approval process.
SHS approval drawings may include only the flow schematic and bill of materials; dimensional drawings are not usually provided. This approval stage is a good opportunity for the user to work with the supplier to decide the safest and most ergonomic physical layout. This can be followed up with an intermediate shop inspection or an exchange of digital photos and user approval before final assembly to ensure agreement.
The safe handling of hazardous samples should consider (1) double block-and-bleed valve systems to permit safe SHS maintenance without exposing the technician to the sample, (2) single- or double-check valves on SHS cylinder and utility gases to minimize the chance of their becoming back-contaminated with sample, (3) bellows-sealed valves on the sample to prevent sample leakage into the SHS cabinet or the atmosphere, and (4) gas detectors or other telltale devices on outgoing SHS cabinet purges to warn of such leaks.
Ergonomics for individual analyzer technicians should not be neglected. For example, it is possible for different analyzer technicians, one perhaps 5 feet tall and one well over 6 feet tall, to responsibility for the same equipment. Therefore it is a delicate, but worthwhile engineering and design activity to minimize bending, stooping and the use of step stools for servicing frequently accessed devices.
Construction Safety Considerations and Ergonomics
Let us define constructability as the safety and efficiency with which the equipment deliverables on the project are brought on site, set in place and connected to each other. We think of constructability as an issue that goes away after the project is complete. This is true only until the time comes to upgrade, replace or otherwise touch the analyzer system with another project.
Whether in a new or existing operating unit, analyzer shelters and systems are among the last pieces of equipment to be delivered, set in place and connected. Were this not true, they couldd easily interfere with or become damaged by other construction. On the other hand, we must ensure early in the project that the analyzer systems, especially analyzer shelters, fit into the unit where their siting is best for sample fast loops, sample return lines and routine maintenance. Not only must the space be available for the analyzer shelter, but the area must not be so congested with large equipment that the analyzer shelter or system cannot be set in place during construction.
Elevated construction and crane lifts over existing equipment present another set of challenges. Though the typical 10 ft x 12 ft analyzer shelter may weigh but 6 tons, a large crane may be needed to lift it 60 ft up and 50 ft laterally due to the long lever arm and heavy cantilever. In an operating plant, even a 500-lb lift across hazardous material piping often requires a special lift plan, a permit and consideration of alternate ways to safely transport the shelter or system to its point of installation.