By George Schuster, industry specialist, Rockwell Automation
For decades, manufacturers have operated under the notion that they must cut the energy supply to a machine to perform maintenance and other procedures. However, alternative technologies and methods can help maintain uptime and productivity while helping to improve worker safety.
Traditional lockout/tagout (LOTO) approaches require employees to remove power sources to a machine — a time and production-consuming process — before it's serviced to prevent an unexpected restart and potential harm to employees .
This time-consuming process of cutting off power to a machine can create a strong incentive, or in some cases even a requirement, to bypass LOTO to perform certain maintenance tasks.
For example, envision a pharmaceutical plant producing hundreds of thousands of small pills per hour. As the pills move down the line, they can get stuck, causing the machine to jam. Jams might be frequent, requiring maintenance to lock out the machine each time, with production output taking a huge hit.
To make matters worse, some types of diagnostic and set-up work are impossible to do without having some power sources active.
This means that some maintenance professionals are forced to bypass LOTO to complete certain job tasks. Unfortunately, they are putting themselves and other coworkers at risk, as well as not complying with industry regulations. It's no wonder LOTO continually ranks among the top 10 Occupational Safety and Health Administration (OSHA) violations year after year.
The good news: More modern applications of configurable safety methods are allowed in certain circumstances as an alternative to LOTO. Outlined in OSHA standard, 29 CFR 1910.147, these alternative measures safeguard machines and devices without having to cut off the power source completely, allowing authorized workers to safely perform a prescribed service. ANSI/ASSE Z244.1-2003 also outlines the use of alternative measures for tasks considered "routine, repetitive and integral” to the operation of equipment during production.
Because OSHA and ANSI/ASSE both provide guidance around alternative measures — and some discrepancies exist between the two standards — manufacturers often are confused about which standard to follow. For example, the ANSI standard allows for alternative methods in certain situations where the OSHA standard would require LOTO, while OSHA believes the ANSI standard may not provide as much employee protection in those situations.
The best way to make sense of these discrepancies is to refer to both standards when implementing any alternative measure. First, review the ANSI/ASSE standard and then identify any potential conflicts with the federal minimum or applicable state regulations as outlined by OSHA.
While many major tasks do require LOTO, a number of service activities exist where LOTO potentially could be engineered out with an alternative measure — if the alternative measure offers effective protection. These tasks are outlined in OSHA's minor servicing exception and include cleaning, setup, adjustments and jam clearing.
However, the most important consideration in determining allowable alternative measures is whether they will provide the same or greater level of protection as LOTO to comply with CFR 1910.147. All alternative measures must be assessed carefully for their effectiveness in context of the configuration of the machine, the reliability of the safety measures, employee training and other factors. If the procedure doesn't offer the same level of protection as LOTO, it isn't compliant and could result in a citation.
To differentiate between applications that require LOTO and those that allow alternative safety measures, a careful review and grouping of the required tasks must be completed. Also, a risk assessment can help engineers design a new or refurbished machine for alternative measures while following the safety life cycle as defined in standards, such as IEC 62061 and ISO 13849.
At the earliest stage of design, engineers should consider a machine's modes of operation and how people will interact with it. Then they should evaluate whether alternative measures can offer the same protection as LOTO during specific maintenance and servicing tasks. If a machine is mission critical, alternative measures can help the equipment stay as productive as possible.
For example, a press brake in a sheet metal processing plant can have multiple points on the machine that need to be locked and tagged each time a maintenance task needs to be completed. This can cut into a machine's productivity significantly. Instead, alternative protective measures — such as interlocked devices, e-stop buttons and other safety technologies integrated into a comprehensive system design — can cut downtime related to maintenance to a fraction of that with LOTO.
Some acceptable alternative measures include specially designed tools, remote devices, interlocked barrier guards, local disconnects or control switches, which are controlled by the employee performing the maintenance task.
To accommodate the variety of maintenance tasks on a complex machine — each of which might require a slightly different alternative measure — engineers can utilize configurable safety systems. These systems provide the flexibility to perform different maintenance tasks with different alternative measures, all on the same machine.
For example, connecting a configurable safety relay to an interlock switch allows for partial access to a guarded area to accommodate a maintenance or upkeep task. However, if the interlock gate is opened while the machine's motor is still running, the configurable safety relay knows to shut off power to the motor to stop any hazardous motion.
Another example is safe-speed monitoring, which is enabled via certain AC drives. Safe-speed monitoring allows operators and maintenance personnel to access a machine while it is still running, but at a reduced speed.
Alternative measures can help optimize machine operation and maintenance by reducing the time it takes for maintenance tasks to be safely completed. Instead of shutting off power to an entire machine for repairs — effectively stopping operations to tend to certain issues that can happen multiple times a day — alternative measures can systematically reduce meantime to repair. This decreased machine downtime can lead to improved system yield, ultimately benefiting the bottom line.
This modern application of safety technologies also can help keep maintenance professionals safer when completing minor servicing tasks. By offering alternate methods for LOTO that allow them to quickly fix a machine problem, maintenance professionals are less likely to bypass critical safety procedures altogether.
Learn more about Rockwell Automation Safety Solutions. Also on that web page, download the free white paper, “Design Your Safety System for Improved Uptime,” by clicking on the “Technology and Engineering” tab.
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