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Process Analyzer System Safety and Ergonomics II

Sept. 28, 2007
The job’s not done until safety, ergonomics and constructability are taken into account.

Go to www.controlglobal.com/10nichols.html for additional references and information about process analyzer projects and safety.

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.

If much work is to be done inside the analyzer shelter after it is in place, the construction schedule must recognize that a 10 ft  x 12 ft analyzer house, for example, cannot accommodate two electricians, two pipefitters and two analyzer technicians inside at the same time.  In this example, two workers at one time is probably the most that can work safely and efficiently inside the analyzer house.

Analyzer shelter and analyzer system constructability concerns should be raised early in the project scope development, again during construction estimating and again during the construction kickoff meeting.

Safety and Ergonomics

The most effective safety and ergonomic approach is to eliminate the hazard so that it  never needs to be addressed. In other words, if a hot SHS heater does not exist, it will not burn anyone; if there is no heavy gas cylinder to move, it will not result in back injuries; if an arcing relay does not exist, it will not initiate a fire or explosion.

But this is not always possible—samples often have to be heated, gas cylinders must be used in most applications and most analyzer systems have electrical components.  Therefore, we include engineering controls like cage guards around hot surfaces, truck lifts and hand trucks for cylinder handling and purged or sealed enclosures for electrical devices.

The least effective, but sometimes the only approach is administrative controls.  Administrative controls often accompany engineering controls for the times that the latter must be removed or bypassed to effect maintenance and service or operations-required modifications.

Effectively writing and implementing administrative controls requires complete, well-written engineering documentation and trained, well-motivated personnel. Training begins with general safety and technical training. Next, the personnel must be trained to understand and operate the equipment for which they are or will be responsible.

Management of change (MoC) and task safety instructions (TSI) are the most important tools in this process.  The MoC is required in the United States by OSHA 29 CFR 1910.119.  We do not have space here to address MoCs in detail, but it will suffice to state that the MoC for an analyzer system must make operations and maintenance personnel aware of changes to operating procedures, equipment, the operating process; safety requirements; regulations; safety hardware and firmware; failures and failure rates; testing; and documentation.

Task safety instructions (TSI) are a procedural checklist and guide as to how a technician actually performs a specific field task.  For example, the TSI for changing an SHS sample filter might include stepwise instructions to obtain a unit work permit, lockout and tagout the analyzer system, the valve sequence to use plant nitrogen to block and bleed the sample from the filter, the correct filter part number and size, and how to reverse the procedure.

Lock the door!

Most users lock analyzer houses, with only the analyzer technician, analyzer reliability supervisor and a shift or operations superintendent having a key. This practice benefits safety, ergonomics, and reliability by preventing unauthorized personnel from entering the analyzer shelter to (1) take “work breaks” that compromise personnel safety and equipment reliability, (2) store unrelated and unauthorized items in the analyzer shelter, (3) prevent unknown, though often well-meaning, workers from tampering with analyzer systems in such a way that compromises personnel safety, equipment reliability and operations, (4) ensure that all work inside the analyzer shelter is authorized by operations through the work permit, lockout/tagout and personnel safety headcount procedures, and (5) ensure that work is documented in maintenance work logs. Analyzer systems installed only in field cabinets should be locked for similar reasons, with similar access control in place.

Users should always comply with the latest appropriate national, state and local codes, industry standards and practices, and corporate and site standards and practices before designing, engineering, constructing and operating these types of equipment.

In this and the previous article, we have reviewed some major safety and ergonomic challenges often encountered in the design, engineering and operation of analyzer systems.  Readers undoubtedly have many specific examples and concerns to add to those in this discussion.  Therefore, readers are encouraged to develop their own lists, based upon the codes, regulations, company, specific site and operating unit needs, and personal experience and work across disciplines and along process analyzer system life-cycle stages to ensure that analyzer systems and shelters are as safe and ergonomic as available technology allows.


Go to www.controlglobal.com/10nichols.html for additional references and information about process analyzer projects and safety.

Gary D. Nichols, PE, is a principal control systems engineer at Jacobs Engineering Group. He can be reached at [email protected].

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