Safety Is Good Business

"The cost of an accident, in terms of legal action -- including possible fines and lost production -- will greatly outweigh the costs of purchasing and installing safety equipment. Added weight is given to this argument because companies not investing in safety equipment can still incur disastrous costs -- even when accidents do not occur." -- Derek Jones, EJA Ltd.

With the recent downturn in the economy, companies are going back to a bare-bones philosophy to remain successful: maximizing profits and minimizing loss. And while industry is achieving this by a number of methods, there''s one that most wouldn''t expect -- plant floor safety. In 1999, when Forbes published its list of the most successful corporations, many of the top 100 were participants in the Voluntary Protection Programs (VPP) (Source: Jerry Laws, "Assuring Best Practices," Occupational Health & Safety July 2000: 92-94) sponsored by the Occupational Safety and Health Administration (OSHA). These programs are only open to companies implementing safety programs that exceed OSHA standards and result in lost time rates at least 50% below their respective state average. Not only do these companies set a new benchmark in health and safety management best practices, but they verify the correlation between plant floor safety and profitability.

It took some time before these manufacturers realized that safety measures weren''t a hindrance to productivity and that safety was truly an investment with positive return. The acceptance of safety as a good business practice is evident as the number of workplace injuries continues to fall each year. But can that positive return be measured? As budget cuts continue throughout many industries, there is increasing pressure to determine what programs are the most valuable, in financial terms, and where cuts can be made. In these cases, plant safety programs and safety professionals have historically been easy targets for cutbacks, simply because the true value of safety is not easily calculated. Hard data on the price tag of lost time accidents is what is required to show that safety has economic value -- and is good business.

By offering such tools, OSHA shows it has shifted its focus from one of standards enforcement, penalties, and fines to one of compliance assistance, stressing the value-add capabilities of safety programs. In his first press conference, OSHA''s recently inducted Assistant Secretary of Labor for Occupational Safety and Health, John Henshaw outlined his plan to stress the value of safety and convince employers that safety is good business.

The goal: to not only get companies to embrace accident prevention, but to help them understand the purpose and value of the standards that affect them. Outlining safety''s benefits in terms of profitability is crucial to achieving this goal, and Henshaw stresses that relaying the message to small businesses will be a priority.

Successful companies can become even more so through aggressive safety programs. Safety is good business -- and the greater the effort placed on safety, the more it pays.

Ignoring the popular adage "If it ain''t broke -- don''t fix it," railway companies are looking to replace aging controls with more reliable, intelligent technology. Why? "Because unlike traditional manufacturing processes, railroad accidents cause more than just downtime and loss of product," explains Dwayne Edwards, general supervisor of signals and structures at Paducah & Louisville (P & L) Railway. "Derailments, combined with the hazardous contents and the sheer weight of freight cars, can quickly lead to casualties, evacuations, and a very unforgiving public."

Railway companies taking the proactive approach to control technology literally have one eye on the tracks, and one eye on the transportation market. With more than 40% of U.S. freight moved by rail, the railroad industry''s market share currently surpasses all other single modes of transportation. The railroad''s lead on trucks, planes, and barges is attributed to providing customers with high quality service at the lowest possible price. But while the more than 550 U.S. freight railways have primarily relied on "good ole'' elbow grease" to maintain this position, companies such as the P & L Railway are now augmenting hard work with new technology.

With 281 miles of main line used to transport more than 15 million tons of coal, chemicals, and supplies annually, P & L is recognized as one of the premier regional railroads in the United States. Its tracks in western Kentucky are strategically located to provide customers access to both the inland waterway system and five of the eight national or "Class I" railroads.

Beyond miles of track and yearly volume, P & L is most proud of its exceptional safety record. In fact, P & L has received accolades from the prestigious E.H. Harriman Memorial Institute and other industry groups for its safety performance.

This is no small feat when taking into account that the entire rail industry is hampered by a lack of capital for ongoing improvements. In terms of profitability, the rail industry averages a 7% rate of return on net investment.

"Our approach rests on the fact that to have a safe operation, we need safety-oriented employees that use their heads," Edwards says. "We empower our employees to always take the safe course of action while looking for and recommending ways to ensure personal safety for themselves and fellow employees as well as operational safety."

Working on the Railroad

The most recent safety initiative at P & L involved auditing and improving the technology used on one of its signaling systems. Much like a typical road, a freight train''s movement through an intersection is governed by green, yellow, and red signals. These indicators control train movement through an integrated series of signal blocks. Each block consists of 10 or more miles of track, and train crews carefully watch signaling systems located at the entrance and intermittently within the block to know what pitfalls, if any, lie ahead. Some of the most common roles of a signaling system are to alert trains to the presence of other trains, broken rails, and improperly functioning switches within the block.

Advance warning is especially important when it comes to rail transportation due to the time it takes trains to stop. For example, a train traveling 35 miles an hour requires more than a mile to come to a complete halt. Any obstruction on the track short of this distance risks collision with the braking locomotive. And since most trains travel faster than 35 miles an hour and have loaded cars weighing more than 100 tons each, the collateral damage of such an event can be devastating.

Chugging Along With Old Technology

While the P & L signaling systems haven''t been a problem to date, the company chose to focus on them due to their aging control technology and the phenomenal risks associated with a potential failure.

"Some of the control technology used in signaling systems is up to 60 years old," said Edwards. "There comes a point in time when you need to replace this technology even though it is properly functioning."

P & L was especially interested in incorporating technology that was certified fail-safe and met the new guidelines set forth in the International Electrotechnical Commission (IEC) 61508 standard for functional safety of electrical, electronic, and programmable electronic safety systems. "The safety guidelines and product testing procedures are much more advanced than in the past, and the resulting quality assurance is priceless in an industry like ours," Edwards explains. P & L was also attracted to the possibility of reducing ongoing maintenance.

Getting the Green Light for a New Solution

"We calculated that by replacing some of the relays and other mechanical components, we could reduce maintenance of a signaling system by as much as 50%," says Edwards. This calculation proved correct when P & L updated the signaling system on one of its drawbridges.

As the name implies, a drawbridge is ''drawn'' to allow safe passage of boats and lowered to allow safe passage of trains. And like other signaling systems, drawbridge equipment has zero tolerance to failure. Even a single short-circuit can lead to a barge colliding with a half-raised bridge -- or a train moving forward before all bridge interlocks are in place. Such nightmare scenarios drove P & L to update its Rockport drawbridge, spanning 520 feet over Kentucky''s Green River.

The drawbridge was built in 1931 and is equipped with a bascule-type lift, which lifts up with the help of a hinge-like component on one end of the bridge span. On a daily basis, 8 to 10 trains and an equal number of watercraft encounter this particular bridge. The P & L train dispatcher, located 120 miles away in the city of Paducah, remotely controls the bridge''s position and monitors its operational status.

For example, a barge traveling down the Green River contacts the train dispatcher via radio and requests permission to pass. If there are no trains within the block (Beaver Dam, KY to Central City, KY), the train dispatcher triggers a raise request, which the signal system recognizes, and the train control signals display a red "stop" signal. After a preset time the bridge will begin to lift and, when fully raised, a green "proceed" signal will be displayed for river traffic. The barge continues its course down the river and radios a message to the dispatcher after clearing the bridge. The train dispatcher will then request the bridge down, and the river traffic signal will display a red "stop" signal. Once the bridge is in the down position, a series of system checks begins. If all checks are verified complete and in the proper sequence, the train control signal will display a green "proceed" signal. Any interruption or out-of-order event results in an immediate red "stop" signal for all incoming traffic and a "trouble call" to a maintenance engineer.

The behind-the-scenes technology of the old system included:

• 48 relays


• Conventional DC track circuits


• An aerial cable running from pole lines situated along the bridge


• A 110 volt DC power switch machine


• A linkage system consisting of steel rods, joints, plates, and bars.

Here''s how it worked: Conventional DC circuits sent current for signal control to the relays, circuit controllers, and switch machine situated along the bridge by means of the aerial cable. The relays monitored the 14 bridge interlocks or "safety checks" and worked with the complex switch machine to drive the rail locks. Interlocks, such as those monitoring the span-lock or lift-rail surface position, were crucial to ensuring zero failure. The lift-rail surface position, for instance, ensured that the running surface of a rail was within a 3/8 in. margin, indicating that the bridge was in the correct position after being lowered. Unless all interlocks were in place, the watercraft or train could not receive a green "proceed" signal.

A Solution From the Wrong Side of the Tracks

From a maintenance standpoint, the drawbridge''s relay-intensive, mechanical solution required several engineers to spend two days a month at the bridge to perform general maintenance tasks, in addition to the scheduled weekly, monthly, and biannual safety checks unique to P & L, and lubricating the more than 60 mechanical pivot points on the bridge.

When P & L looked closely at the drawbridge solution, there were numerous problems the company needed to address. First, the relays -- being mechanical devices -- required a significant amount of attention and, with moving parts, were prone to wear. The pole lines used to carry the current for signal control dated back to the days of the telegraph, indicating that the structural integrity of the poles was questionable. Also, the signal provided by the conventional DC track circuits didn''t carry well, which could easily result in a short circuit. Overriding all of these problems was the fact that there was no documented safety rating on any of the hardware used, leaving P & L vulnerable in the event of an accident.

To address these inadequacies, P & L worked closely with Interrail Signal, Inc. of Jacksonville, Florida, a systems integrator that focuses on improving the safety and reliability of railroad signal systems. The new solution designed by Interrail included:

• An Allen-Bradley GuardPLC™ 1200 controller


• 16 relays


• Four non-ferrous selective proximity sensors


• Coded electronic track circuits

The backbone of P & L''s new solution is the Allen-Bradley GuardPLC 1200 from Rockwell Automation. A certified, fail-safe programmable controller, the GuardPLC is designed to monitor the bridge sequence and all of the interlocks, span locks, and lift rails to ensure the accurate raising and lowering of the drawbridge. By replacing the switch machine, linking system, and 30 relays with the PLC®-based system, P & L is left with far fewer mechanical components to maintain. As a result, the company can now eliminate four days of maintenance each month.

A Certified Safe Engine

The single most important feature of the PLC is its fail-safe components. The GuardPLC uses redundant CPUs in a single PLC controller body. Each of the logic circuits within the controller -- supporting digital and analog inputs, outputs, timers, and counters -- contains several checkpoints.

If a failure is monitored, the PLC is designed to conduct an orderly equipment shutdown.

Since the highest safety integrity level (SIL) that can be claimed for the entire signaling system is limited by the fault tolerance of its subsystems, the certification of every component is critical.

IEC 61508 provides four safety integrity levels. The top-most level (SIL 4) is applied to equipment traditionally used on aircraft and in nuclear power plants. The GuardPLC1200 is certified at SIL 3, which is the safety apex for the railroad industry. IEC 61508 dictates that SILs are determined by two operating modes: the average probability of the equipment to fail its assigned function on demand, and the probability of dangerous failure per hour of operation in high-demand or continuous mode of operation.

In addition to maintaining a safe state of continued operation, the GuardPLC 1200 provides a scalable safety control system that is easily programmed with the RSLogix Guard™ programming and configuration software. Glen Tyson, of Allen-Bradley distributor Englewood Electrical Supply, helped create the sequence for P & L. As a PLC specialist, he was able to quickly create the program, taking advantage of the built-in and user-defined function blocks within the RSLogix Guard software package.

Glen also designed an input simulator to test the accuracy of the GuardPLC sequence before it was installed. "This was critical because any downtime after the GuardPLC went online would cause extensive delays for trains and boats," said Jim Kelley, president, Interrail Signal. "The simulation gave us the assurance we needed that the controller would perform as expected."

The Safety Caboose

In addition to the safety PLC, P & L replaced the conventional DC track circuits and aerial cable with coded electronic track circuits that send pulses in different code rates along the rail. Each code rate represents a unique signal color or message to the receiving unit. The coded electronic track provides state-of-the-art signaling capabilities, reducing the risk of having relays short-circuit. And non-ferrous selective proximity sensors, which are capable of differentiating between the steel tracks and their stainless steel targets, are used to indicate the position of the bridge''s span locks and lift rails. This ensures that locks and rails are in their proper position.

In addition to reducing maintenance by 50%, the Allen-Bradley GuardPLC and proximity sensors helped P & L eliminate a lot of the mechanical components that are costly to replace. "Our new hardware cost 10% of what we would have paid to replace the switching machine, linking system, and other devices previously used on the bridge. But saving hardware cost was not one of our primary goals going into this," said Edwards. "Above all, we now have a more reliable, streamlined operation."

Neapco, a Pottstown, Pennsylvania-based manufacturer of powertrain components, needed a way to protect their employees from the movement of an X-Y table on a machine tool. After reviewing possible solutions, a pressure-sensitive edge-detecting system was selected and installed.

Formed about 75 years ago, Neapco builds parts for automobiles, agricultural equipment, and heavy-duty earth movers. Neapco is quite quality conscious -- their quality system is registered to both ISO9001 and QS9000 -- but their main concern is employee safety. The machining operations required for Neapco''s production had been in place for some time, but a year ago, another manufacturing operation was required. A new multi-process machine capable of drilling, milling, and cutting was installed. This machine features an automated table that moves in an X-Y plane as parts are processed. Soon after installation, it became obvious that the moving X-Y table was a hazard and that measures would have to be taken to ensure employee safety.

When evaluating the risks of the machine, several factors were taken into consideration: the tasks required of the operator and the hazards associated with them, other machine hazards not associated with those tasks, the frequency of exposure, and the severity of the hazard. For the purpose of this article, the risk assessment is focused on the issues surrounding the X-Y table of the machine.

The Severity

The severity of injuries that could be sustained by an employee as a result of X-Y table movement was determined to be low based on the table''s speed. The table moves at 472 inches per minute, a speed at which incidental contact with the table would not cause death or loss of limb. If the X-Y table struck a person the resulting injury would, at most, be a good-sized bruise and the employee would fully recover in a short time.

The Tasks

The tasks directly associated with the movement of the X-Y table are the loading and unloading of parts by the operator. This is generally a low risk situation as the X-Y table is not moving during these stages of the process.

The Hazards

The hazards of the X-Y table not directly associated with machine tasks are the major concern for a number of individuals in different scenarios.

The operator runs multiple machines. After loading parts on the X-Y table, the operator puts the machine in automatic mode. The machine then performs drilling, cutting and milling operations automatically. While the operator performs tasks on other machines and moves about the work cell, the X-Y table is moving side to side, forward and back, depending on the operation. An experienced operator might be able to anticipate the movement of the table after a few cycles, but a change in the machine''s program might catch the operator off guard. New operators not familiar with the table''s patterns of movement are at an even greater risk of being struck by the X-Y table.

The location of the machine plays a role in the risk analysis. Located along an aisleway, the machine is surrounded by a yellow line painted on the floor that outlines the range of X-Y table movement. While movement of the X-Y table does not extend into the aisle, employees may inadvertently enter the unsafe area around the machine in the course of their everyday activities. Material handlers using pallet jacks to move parts in neighboring cells are at risk of being hit by the X-Y table if they accidentally back into the hazardous area. With a fork truck in the aisle, passersby getting around the fork truck may put themselves at risk by walking into the area surrounding the table. Since the X-Y table moves without operator interference when in automatic mode, it is possible for anyone in the wrong place at the wrong time to be struck by it.

Other people that might be in the aisles or in the work cell include quality inspectors, engineers, managers, customers, suppliers, and janitors. People in these and similar roles could possibly move into the hazard zone at some time while the machine is operating. Although the severity of the hazard is low, the possibility of an accident is relatively high and continuous.

The Challenge

The challenge of this safeguarding application was the selection of a method that would provide ample protection while allowing the operator to move freely around the machine cell, run the other machines, and maintain the current productivity levels.

The Options

A number of possibilities were evaluated for the application.

One option was to position hard barriers around the machine that would protect the operator and passersby. Although this option provided the necessary guarding, there were a couple of drawbacks. Barriers would occupy valuable floor space. Plus, a rather complex access point would have to be created requiring an access door with interlocking. Barriers would have to be designed with this in mind. Maintenance of the machine might also require temporary removal of the guarding. Ultimately, barriers were deemed unsuitable as they would hinder productivity by creating loading /unloading constraints and making movement in the work cell more awkward. Downtime due to tool changes and maintenance would also be higher.

Another possibility was the use of proximity-type detectors. While this solution eliminated the concern of the excessive floor space taken up by the hard barrier guards, Neapco did not have confidence that the technology could provide consistent and adequate protection.

Neapco turned to Fromm Electric Supply Corporation of Pottstown, PA, an authorized distributor of Rockwell Automation industrial control and safety products. Jill Klodowski, iIndustrial control specialist, recommended the Allen-Bradley Guardmaster GuardEdge™ pressure sensitive safety edge system as a possible solution.

This idea appealed to Neapco, but further evaluation was essential. Could the pressure sensitive edges be installed on the corners of the X-Y table and still effectively detect the presence of a person? Would the rubber hold up to the machining fluids being used? Would the sensor continue to operate if it were cut or damaged? Was the sensor edge easy to install? Dedicated to providing a safe working environment, Neapco employs an on-site safety coordinator and a safety committee performs monthly audits and walk-throughs in an effort to prevent accidents. The solution was reviewed by the safety coordinator and considered acceptable if it could hold up against the work cell environment.

The Solution

The GuardEdge pressure sensitive safety edge solution effectively met the requirements of the application. According to Bob Dixon, manufacturing engineer at Neapco, "The Rockwell area manager, Bill Stone, provided strong support during the specifying and installation of the GuardEdge product. That helped make the process of getting safety into an operational state easier."

Plant personnel assembled the sensor edge quickly and easily. Special brackets were fabricated to hold the edge in place at the corners of the X-Y table while keeping the corners active to sense personnel. The heavy-duty rubber construction of the edges was also tough enough to stand up to the environment, especially the associated machining fluids.

The output of the GuardEdge controller was connected in series with table power. In the event that someone bumps into the table edge, the table comes to an immediate stop and the machine program halts. Once the operator hits the reset button, the machine program continues from the point of the interruption.

Neapco continues on its path to providing a safe working environment. The GuardEdge pressure-sensitive safety edge system helped Neapco achieve its goal in a cost effective and efficient manner while providing the required safeguarding of the machine hazard.

As industrial automation broadens to accommodate a more global marketplace, equipment manufacturers and users are applying international standards to their installations. In no area is this more true than in machine safety. Historically, safety and productivity have worked against each other on the plant floor. With the latest developments in machine safety products, this is no longer the case. Past sentiments dubbed machine safety as merely an expense; that notion has evolved into the acceptance of safety as an investment that may actually increase productivity.

Safety and Progress

When machines entered the picture during the Industrial Revolution, the idea of worker safety was secondary to productivity and, more directly, money. Accidents were common, and there was no incentive for business owners to make safety a priority. A "laissez faire" system had been established that allowed the business owners free reign of their businesses without interference from the government. So while productivity was soaring higher than ever before, unsafe machines and dismal working conditions were also taking their toll on the workforce. In the 19th century, however, things took a turn for the better; edicts on acceptable working environments and safe machine practices began to emerge.

By the beginning of the 20th century, true machine safety products started to appear in the form of emergency stops. World War II saw the introduction of safety control relays that could provide electromechanical diagnostics through the use of interlocking contacts. But the most dramatic leap in machine safety started in the latter half of the century -- and safety products haven''t stopped evolving since.

In the 1960s, fixed machine guards came to the fore as the primary method of protecting personnel from hazardous machinery. Driven by legislation, the installation of these cages and barriers basically prevented access to the machine. Fixed machine guarding (also known as ''hard guarding'') provides the most effective protection by not allowing anyone near the point of hazard but, unfortunately, it is not a feasible solution when the application requires routine access by an operator or maintenance personnel.

By the 1970s, movable guards with interlocking systems became the most prominent solution for applications requiring access to the machine. Hinged and sliding guard doors outfitted with safety interlock switches allow access to the machine but cut off machine power when the guard is open. Some interlocking systems also contain devices that will lock the guard closed until the machine is in a safe condition -- this is known as guardlocking. In the first step toward the integration of safety and machine control, the interlock solution allows for a degree of control while restricting access during unsafe stages of the machine''s operation. In terms of the marriage between safety and productivity, the combination of movable guards and interlock switches is still the most reliable and cost effective solution for many industrial applications. However, in processes requiring more frequent access to the machine, repeated opening and closing of guards is detrimental to cycle times -- even a few seconds added to each cycle can severely hamper productivity when you''re talking about hundreds of cycles per day.

Presence-sensing devices for safety applications made their way onto the plant floor in the 1980s with the introduction of photoelectric safety light curtains and pressure-sensitive floor mats and edges. Designed to isolate machine power and prevent unsafe machine motion when an operator is in the hazardous area surrounding a machine, safety sensors help provide personnel protection without requiring the use of mechanical guards. They are also less susceptible than interlock switches to defeat, bypass, or tampering by the machine operator. The sensors'' use of solid-state technology also provides a degree of diagnostics not previously possible in systems using relay control with electromechanical switches.

Fifty years'' worth of safety advances culminated in the safety control domain of the 1990s -- the integration of hard guarding, safety interlocks, and presence-sensing devices into a safety system monitored and controlled by a dedicated safety controller and integrity monitoring. Trends show that this safety evolution will continue to move toward seamless control solutions involving electronic safety systems, high-level design tools, networking capabilities, and distributed safety implementation through embedded intelligence.

Global Standards for a Global Market

Safety in automation is not new, but as global distribution of products becomes the norm, machinery manufacturers and end users are increasingly being forced to consider global machinery safety requirements when designing equipment. One of the most significant standards is the Machinery Directive, which states that all machines marketed in the European Union must meet specific safety requirements. European law mandates that machine builders indicate compliance with this and all other applicable standards by placing CE -- the abbreviation for "Conformite Europeenne," which translates to "European Conformity" -- markings on their machinery. Though European in origin, this safety-related directive impacts OEMs, end users, and multinational corporations everywhere.

In the U.S., companies work with many organizations promoting safety. Among them:

1. Equipment purchasers, who use established regulations as well as publish their own internal requirements;
2. The Occupational Safety and Health Administration (OSHA);
3. Industrial organizations like the National Fire Protection Association (NFPA), the Robotics Industries Association (RIA), and the Society of Automotive Engineers (SAE); and
4. The suppliers of safety products and solutions.

One of the most prominent U.S. regulations is OSHA Part 1910 of 29 CFR (Title 29 of the Code of Federal Regulation), which addresses occupational safety and health standards. Contained within Subpart O are mandatory provisions for machine guarding based on machine type; OSHA 1910.217, for example, contains safety regulations pertaining to mechanical power presses. In terms of private sector voluntary standards (also known as ''consensus standards''), the American National Standards Institute (ANSI) serves as an administrator and publisher, maintaining a collection of industrial safety standards including the ANSI B11 standards for machine safety.

With components sourced from around the world, the final destination and use of a product often remains unknown to its manufacturer. As a result, machine builders are looking to suppliers not only for safety products that meet global requirements and increase productivity, but as a useful resource for an understanding of safety concepts and standards. And in an effort to more efficiently address customer concerns and stay abreast of the market, those suppliers have assumed an active role in the development of standards.

Safety and Productivity Can Go Hand in Hand

Safety is, above all, about protecting personnel. Today''s manufacturers, for the most part, are beginning to view safety as an investment with a positive return in the sense that a safer workplace boosts employee morale; machine operators feel more comfortable with the equipment and are aware of the company''s commitment to their safety. The result is increased productivity and savings attributed to a decrease in loss-time accidents, medical expenses, and possible litigation.

As machine industry safety standards continue to become statutory requirements, manufacturers are often faced with added costs associated with products meeting safety regulations. Consequently, some manufacturers view purchasing and installing safety products as an expense. And users naturally wonder if this is an expense never to be recouped, or a long-term investment that can result in higher productivity.

Traditionally, safety and productivity in a manufacturing plant pulled in opposite directions. The safer a system was, the less productive it was. But this is no longer the case. Today''s safety systems can provide a level of enhanced productivity while meeting global safety requirements.

Investing in solutions as simple as ergonomic palm buttons, designed to relieve operator strain and decrease repetitive motion injuries, helps manufacturers meet safety requirements while increasing production. In one example, a series of Zero-Force™ Touch Buttons were installed on an industrial seal line in which operators previously had to depress 2-pound buttons during the entire 5-second cycle. Using standard buttons, these operators suffered neck and shoulder soreness during their shifts. After installing the Zero-Force touch buttons, employees no longer complained that the machine was causing discomfort. The buttons created better working conditions that have directly affected employee morale, decreased employee injuries, and led to a more productive plant.

Another example of how advanced safety products can improve productivity involves light curtains, infrared light barriers that detect operator presence in hazardous areas. Typically, a safety interlock gate is used to help prevent machine motion when an operator enters the hazardous area. Even if it only takes 10 seconds to open and close that gate for each cycle, that time accumulates over the course of a 200-cycle day. If the traditional gates were replaced with light curtains, operators would simply break the infrared barrier when entering hazardous areas and the operation would come to a safe stop. Over time, the light curtain investment would increase productivity and create a positive return.

In addition to the safety function, protective light curtains may also serve as the means of controlling the process. Known as Presence Sensing Device Initiation (PSDI), breakage of the light curtain''s infrared beams can be used to initiate machine operation; upon breakage of the beam, the machine stops to allow for part placement and the completion of the beam after the operator removes his or her hands from the point of hazard restarts the machine process.

Manufacturers'' desire for continuous machinery operation without compromising safety has led to the merging of control and safety systems. This combined safety and control domain will allow facility engineers to do routine maintenance or troubleshooting on one section while production continues on the rest of the line, safely reducing work stoppages and increasing flow rates. For example, in most of today''s plants a robot weld cell with a perimeter guard will shut down entirely if an operator walks into the cell and breaches the protected area. Control systems using safety PLCs tested to Safety Integrity Level 3 (SIL 3) -- the highest level defined by the IEC for microprocessor-based safety systems -- can actually isolate a hazard without powering down an entire line. This permits the area undergoing maintenance to be run at a reduced, safe speed suitable for making running adjustments. The result is an easier-to-maintain manufacturing cell, and one that is quicker to restart.

In a downtime situation with a lockout/tagout operation, system operators may have to use five or 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. If a safety control system with diagnostic capabilities were installed, operators could shorten the lockout/tagout process, quickly troubleshoot the system, and get the system up and running.

Previous generations of safety products were able to make only some of these things happen. But current safety products, and those of the future, can and will increase productivity from another angle -- not only are today''s machine guarding products faster and safer, but their integration may actually boost productivity by enhancing machine control.

A Final Word

The increasing effect of standards and legislation -- especially global -- continues to drive the safety market. But even with those tough standards in place, today''s safety systems have helped dispel the notion that safety measures are a burden. Ultimately, the good news for today''s manufacturers is that safety products can now provide the best of both worlds: operator safety that meets global regulations and increases productivity.