How to Tell if You’re Paying Too Much for Safety

10,000 safety PLCs and 360,000 safety network nodes worldwide don’t lie – integrated safety systems reduce long-term ownership cost.

Over the past several years, safety has emerged from an afterthought to become an integral component in many industrial systems. Now, machine builders and end users enjoy the benefits of new machine guarding technologies endorsed by international safety standards that bring economical and effective choices to machine safety.

Safety is now an integral design element. The latest options include integrated, networked systems that use safety PLCs. Designed and built according to IEC guidelines and tested by nationally recognized testing laboratories such as Technical Inspection Association (TUV) and Underwriters Laboratories (UL), Siemens SIMATIC Safety PLCs, buses, I/Os, and other components are replacing traditional hardwiring on machines.

Enhanced operator protection is a necessity. One study placed machine-related injuries among the most common types of workplace injuries. The fatality rate from machine-related accidents was second only to motor-vehicle-related accidents, recording higher fatality rates than homicides, falls, and electrocutions, according to the National Institute for Occupational Safety and Health (NIOSH).

In addition to protecting machine operators, enhanced machine safety machine brings other benefits to builders and end users. Control costs are lower, time to market is shorter and downtime is reduced, as is litigation.

Incorporating safety into machine designs begins by understanding recent changes in international safety standards and regulations. Then, it is simply a matter of applying the appropriate safety options to meet these requirements, including total lifecycle costs in the decision-making process.

Companies that implement safety functions, perform functional safety evaluations, and implement safety in manufacturing processes are finding benefits where few expected to—on the bottom line. Downtime and injury-related expenses can be reduced, while the potential for greater human interaction with the automated equipment can improve productivity.

Safety is now addressed by a number of improved standards. Standards from the National Fire Protection Agency, ANSI B11.0 Safety of Machinery and ISO 12100:2010 have all  been revised in recent years, and designers have embraced them. The EU’s Machinery Directive. EN/ISO 13849-1 (“Safety of machinery – Safety-related parts of control systems – Part 1 General principles for design”) is also a mainstay in many safety designs.

Risk assessment has become an important tool for compliance with the essential health and safety requirements. It protects against allegations of negligent or even culpable action and, in some cases, against possible consequences under criminal law.  If applied correctly, it can result in cost savings.

The risk analysis reference in ISO 12100 formalizes what has been a requirement all along, but wasn’t an absolute standard. Now, a formal process must be followed to evaluate risk potentials throughout all modes and operations of a given machine. This process identifies all risk levels that could injure the operator, maintenance personnel, or even individuals walking past a machine.

These devices can significantly lower the cost of single- and multi-zone applications by allowing one device to be wired to the entire safety circuit, networking to each individual device. This significantly lowers the cost of wiring and permits fast troubleshooting while allowing individual safety incidents to be monitored. It is a very good solution for safety systems with relatively low complexity, with only two or three safety zones.

Safety Strategy Options

The right safety strategy can provide a competitive advantage for the machine builder and manufacturer.  Choosing the right option can result in quicker time-to-market with higher product throughput, and lower total cost of ownership for safety systems, improving both overall equipment effectiveness (OEE), and return on assets (ROA). Here are four safety options to consider:

Dedicated safety relays have been a mainstay of safety circuits for decades. While effective, their overall costs may outweigh the benefits. They can also limit the ability to monitor and troubleshoot machines since emergency stop buttons are often wired in series to decrease wiring costs, which makes troubleshooting difficult

Networked safety relays can significantly lower the cost of single- and multi-zone applications by allowing one device to be wired to the entire safety circuit, networking to each individual device. This configuration significantly lowers the cost of wiring to enable rapid troubleshooting, while allowing individual safety incidents to be monitored. It is a very good solution for safety systems with relatively low complexity.

Dedicated safety PLCs may be added to systems that already have a PLC. This adds monitoring capabilities to the system, but it has two major challenges. The safety PLC adds expense and it introduces another programming language to learn, implement, and troubleshoot.

Integrated, simplified safety systems combine the functionality of a control system and a safety system into one PLC, greatly reducing life cycle costs on a machine. Siemens SIMATIC S7 PLC, for example, combines integrated control and safety into one controller. Implemented in more than 10,000 applications, manufacturers have saved millions in overall costs. This integrated safety system allows all data to flow to the human machine interface (HMI) for fast and easy troubleshooting.

Design and implementation are simplified because same programming language is used for control and safety circuits. Wiring is simplified by using safety networks to monitor and/or control each device on the safety circuit. Troubleshooting is often cut by 60-80 percent since each networked safety device communicates via the same HMI, as the rest of the control system.

These advantages significantly reduce downtime and the costs associated with failures. An integrated safety system also makes it nearly impossible to bypass the safety circuit by jumpering out a safety device, including a door switch or light curtain.

Many other benefits accrue. Larger numbers of safety devices can now be connected on the network, such as failsafe motor starters and safety drives. Most of these devices have traditionally been hard-wired and provided only a minimal level of diagnostics. Wireless safety is a growing trend in automotive and aerospace assembly operations, warehouses, distribution centers or material handling applications where it is difficult and expensive to do all the wiring required to integrate the safety systems.

Unless a machine employs only one or two safety relays, a networked safety system using a single PLC will deliver far greater benefits than traditional hardwired methods. Improved machine safety, reduced time to market, and lowered lifetime cost may be achieved by working with an experienced automation and safety advisor.

Siemens, for example, has implemented more than 10,000 safety PLCs and 360,000 safety network nodes worldwide. Siemens engineers understand and consistently monitor the changes in ongoing international safety standards and regulations. No other automation company has greater experience in applying the appropriate safety solution based on the application.

For more information on how integrated machine safety can work for you, go to www.usa.siemens.com/safety.

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