An effective passive system design performs its function automatically, with little if any effort required on the part of the user. When intelligently applied, a passive design can help boost productivity.
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Explore This IssueJune/July 2010
In many production operations, for example, food processors and packaging companies use a light curtain to help prevent machine motion when an operator enters a hazardous area. Other approaches, such as a safety interlock gate, require operators to perform a task to initiate the safety function. Even if it only takes 10 seconds to open and close the gate for each cycle, that time accumulates over the course of a 200-cycle day. With a light curtain, the operator simply breaks the infrared barrier when entering hazardous areas, and the operation comes to a safe stop. Over time, this passive design helps increase productivity and creates a positive return.
The Configurable Design
Another approach that limits exposure to hazards and reduces the incentive to bypass the safety system is a configurable design, which allows operators to alter the behavior of the safety system based on the task they need to perform.
For example, an operator who needs to access a machine may also require some form of power to perform a maintenance function, clear a jam, or teach a robot. The initial risk assessment identifies and defines all the tasks, including these, that must be performed on the machine, with or without power. The assessment will help create a configurable design that meets global safety requirements, increases productivity, and reduces the incentive to bypass the system. In most cases, inexpensive components such as push buttons, selector switches, and lights are all that is needed to achieve an acceptable level of safety.
Using a lockable system design to systematically reduce mean time to repair (MTTR) can help boost productivity. Using this approach, operators can select a safety configuration and then lock it in place at the point of entry. In addition to helping to protect configuration changes, a lockable design also results in higher productivity by using the safety system in lieu of lock-out/tag-out (LO/TO) for many routine maintenance and setup procedures.
For example, in a LO/TO situation, operators may need to use six locks to safely shut down a line, including electronic, pneumatic, and robotic systems. Shutting down the entire machine can be time-consuming and inefficient, causing excessive downtime that hinders productivity. A safety system that meets the target safety level and complies with standard ANSI Z244-1 can be used to disable the hazards. In this case, LO/TO is not required. Instead of locking the disconnect switch, operators only lock the safety system.
The potential cost savings associated with reducing the LO/TO downtime by even a few minutes can be substantial. If a manufacturer reduces MTTR by two minutes using this lockable design approach, the annual savings is substantial. For example, if the value of one minute of downtime is $10,000, and the plant averages 3,000 downtime events per year (eight per day), the value of the safety solution equates to roughly $60 million per year.
The far-reaching economic benefits of a well-designed safety system are too significant to overlook. Using reliable safety technology and the rigorous approach defined in the safety life cycle, manufacturers and machine builders can harness the inherent value of intelligent safety system designs to drive productivity, reduce labor costs, and, ultimately, increase the bottom line. ■