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From: Food Quality & Safety magazine, June/July 2010

Intelligent Safety Design Improves Productivity

Safety a catalyst for meeting greater performance standards

by George Schuster

Ask any food production line manager about the importance of safety, and he will likely tell you about the critical role it plays in protecting personnel, reducing injuries, and meeting compliance demands. These are all valid objectives, but food processors, packaging companies, and machine builders are missing opportunities to respond to the challenges of global consolidation and changing consumer preferences if they only focus on avoiding negative consequences. Instead, they should view safety as a catalyst for greater performance: increased productivity, improved competitiveness, and overall profitability.

Historically, the food industry has viewed safety practices as punitive actions or compliance activities, not as opportunities to deliver real value or to gain a competitive edge. These days, however, food processors and packaging companies understand that a well-designed safety system will improve efficiency and productivity. Machine builders recognize that safety systems will improve both business and machine performance—and help differentiate them from their competitors.

The combination of functional safety standards, new safety technologies, and innovative design approaches is positioning safety as a core system function that can deliver significant business and economic value, with financial returns beyond the benefits of reducing the costs associated with accidents and medical expenses.

As part of the Rockwell Automation Integrated Architecture system, the Compact GuardLogix controllers use the same configuration, networking, and visualization environment as the company’s larger-scale systems. This helps provide cost-effective integration of a machine or safety application into the plant-wide control system.
As part of the Rockwell Automation Integrated Architecture system, the Compact GuardLogix controllers use the same configuration, networking, and visualization environment as the company’s larger-scale systems. This helps provide cost-effective integration of a machine or safety application into the plant-wide control system.

A Systematic Approach

To achieve a higher level of functional safety and to gain real benefits, system designers must have in-depth understanding of food processing and packaging procedures and a clear determination of machinery limits and functions. They must also possess a thorough knowledge of the various ways in which people interact with the machinery. They should take a practical, rigorous approach to safety system design and be willing to implement and apply new safety technologies and techniques.

The functional safety life cycle, as defined in standards IEC 61508 and IEC 62061, provides the foundation for this detailed, more systematic design process for machinery applications. A key objective of the safety life cycle is to address the cause of accidents. To do this, designers want to create a system that will reduce and minimize risks, meet appropriate technical requirements, and ensure personnel competency. Previous standards have relied on prescriptive measures defining specific safeguarding.

The new functional standards are performance based, making it easier for designers to quantify and justify the value of safety. This approach is more methodical and deterministic, with the ability to tailor specific safety functions to the application. It helps reduce cost and complexity, improves machine sustainability, and enables an optimum level of safety for each defined safety circuit or function, thus improving return on investment.

Phases of Safety Life Cycle

Conducting a risk assessment is the first phase of the safety life cycle. A risk assessment provides the basis for the overall risk-reduction process, which involves the following steps:

  • eliminate hazards by design using inherently safe design concepts;
  • employ safeguarding and protective measures with hard guarding and safety devices;
  • implement complementary safety measures, including personal protective equipment; and
  • achieve safer working practice with procedures, training, and supervision.

In safety system design, a risk assessment can help identify potential hazards and the safety mechanisms needed to ensure adequate protection from those hazards. The functional life cycle provides the framework for several highly effective “design-in” safety concepts. These include passive, configurable, and lockable system designs.

A passive approach is based on the philosophy that safety systems should be easy to use and should not hinder production. Operators may decide to bypass safety systems if they are cumbersome or impractical or do not easily accommodate maintenance and operating procedures.

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.

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 functional safety life cycle. The combination of functional safety standards, new safety technologies, and innovative design approaches are positioning safety as a core system function that can deliver significant business and economic value.
click for large version
The functional safety life cycle. The combination of functional safety standards, new safety technologies, and innovative design approaches are positioning safety as a core system function that can deliver significant business and economic value.

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.

Cost Savings

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. â– 

Schuster, a certified functional safety expert, is senior industry consultant for safety and sustainability solutions at Rockwell Automation. For more information, contact Tanja Bartulovic at tbartulovic@ra.rockwell.com or (440) 646-4117. To see how one company used safety solutions to optimize ice cream production, visit http://discover.rockwellautomation.com/SA_EN_Machine_Consumer_Packaged_ Goods.aspx.

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