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Striving for safety in abrasive saw design, cutting processes
Understanding risk assessment sheds light on system and process safety
- By Charles Vosmik
- March 8, 2022
- Article
- Sawing
There’s no denying that many machine tools used around the edges of production environments get little attention. They usually fall into one of two categories: legacy or peripheral. Legacy machines are fully depreciated, essentially free, and therefore kept in service even though they might be in poor repair and present substantial residual risks to the workers who use them. Peripheral machines aren’t central to the operation and therefore aren’t judged to be worthy of investment.
Often, these machines have outdated safety design. With just enough guarding to comply with American National Standards Institute (ANSI) B11, they were intended for limited use in a tool room by highly skilled craftsman. Fast-forward a few decades, as high school vocational programs went by the wayside and the lure of service industry jobs pulled people away from manufacturing, and everything has changed. Now it’s almost impossible to find anyone, at any wage and skill level, willing to stand in front of an open machine all day, dealing with dust, chips, coolant, and sparks, as well as exposure to nickel, cobalt, and other metals. The Great Resignation and the Great Boomer Retirement have accelerated this trend.
OSHA: Striving for Safety, But Not Necessarily Safest
A big, bold line divides safety initiatives into two groups: strict compliance with the law and best practices. Traditional toolroom abrasive saws, for example, are designed and built to be safe at the level of strict compliance. The wheel guards are thick enough and the spark guards are wide enough to comply with ANSI standards, but that’s it. A traditional abrasive saw has no additional systems to monitor and maintain the safety of the process. A tired and distracted operator could unintentionally cut a finger, hand, or arm. Although the machine complies with the law, its use comes with a high level of residual risk.
Functional safety, a relatively new theory of safety design, seeks to mitigate intolerable risks to life, limb, equipment, and environment, balanced against the ability to actually use the tool. It involves designing a machine and process with a safety system or protocol that accounts for both proper and improper operation to reduce or eliminate risks to the operator.
Most modern safety organization’ best safety practices steer designers and users toward a functionally safe process. By following these standards and guiding principles, a manufacturer can proactively mitigate risk and reap the benefits. How does one begin? It’s a matter of learning about and implementing a formal, written risk assessment of every operation or machine in the facility that relies on an operator.
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The Risk Assessment Process
ANSI, ISO, EN, and CE all outline a risk assessment process, ISO/EN12100. All involve rating risks—whether to the worker, machine, or environment—by probability, severity, and type. Rating each risk is a matter of examining every process to uncover every potential hazard.
This must include actions that are typical on the part of the operator in both proper and improper operation. Even when operated properly, a saw poses numerous hazards—laceration and amputation from the blade; potential burn injuries from the sparks thrown from the cutting process and heat stored in the blade; an inhalation hazard from the fine debris produced by the sawing process; crushing and pinching hazards on vises, clamps, rocker arms, and other mechanical devices on the saw; and, depending on the blade, a shattering hazard from improper loading. Adding in the inherent risks of using an electric tool and possible repetitive stress injuries, the tally can be as high as 40 noted hazards.
After identifying the risks comes the hard work: mitigation.
Ready? Design.
The principles of functional safety and control safety (ISO 13849-1) inform the designer that the machine must have more than just an interlock and an enclosure. Based on the level of risk, the machine should utilize fail-safe electrical components and redundant circuitry that disables operation if the access door is not latched. For example, even if the enclosure doors are closed, latched, and locked, a good design may incorporate two-hand touch, requiring the operator to have reasonable intention to start the cycle. This setup protects the operator in a failure situation. If the door is open, the fail-safe system is intended to stop, and prevent starting, motion until the machine is returned to a safe condition.
Regardless of how the guards on a saw are designed, long raw stock needs to feed through to the cutting area to reach the blade. If the feedstock can reach the blade, often a hand can also reach the blade, and this can tempt operators to reach into the cutting area. It’s not uncommon that a saw operator takes a risk once in a while, reaching into the machine to snatch a stub end or to grab a sample piece while the machine is running. Functional safety seeks not to change this behavior outright, but to distance the hazard from these areas through safe-reach distances. An arm-sized hole should be far enough from the hazard that it cannot be reached. A finger-sized hole can be much closer to the hazard, while being far enough away to minimize risk.
In some situations, human-machine interaction is necessary or preferred. Some processes require unique fixturing, making multiple small cuts, or particular part positioning, all of which may bring the operator closer to the hazard than a typical feed-though process. Functional safety practices still allow the operator to execute these tasks. The machine builder might add a light curtain or area sensor to monitor the space around the machine. Another possibility is finger-safe dual-pressure clamping. While the guard is out of the way or the viewing door is open, the vise exerts less than finger-crunching pressure to secure the part. As soon as the operator swings the guard back into place or closes the viewing door, the clamping pressure increases to the amount required to hold the part steady for cutting or machining.
These adaptations reduce the risk to the operator but still leave the machine functional—hence the concept’s name, functional safety. Other applications may require altering the production process to create a new, safer method for completing the task that maintains productivity while minimizing risk, using automation, fixturing, flexible workholding, and similar strategies, which can be deployed successfully even in low-volume/high-mix environments.
Electrical failure or control system failure is another factor in the risk assessment and the other half of functional safety. How is risk managed in a loss-of-power scenario? In the abrasive saw example, the chop saw design relies on the weight of the motor and the force of gravity to pull the blade out of the cut in a power-loss scenario.
However, this design creates a new hazard. Motion is now possible when power is off. The rising saw head creates a potential crushing hazard between the saw and the guard. The solution to this new problem to change the enclosure’s design.
Safety is always an active process. Best practices change and mitigation can create new risks, so it’s important to assess the system for risks continuously.
Is a Safer Machine a Less Productive Machine
“All that safety stuff makes the machine irritating to use.” In the past, this may have been the case. Guards and other safety devices were perceived as cumbersome and adapting to an updated saw wasn’t necessarily easy.
The science of making machines safer is different these days from how it was years ago. Functional safety aims to solve this problem through its focus on functionality. It’s in the name. Functional safety involves the use of electrical devices to monitor the processes end to end. Automation removes some of the burden from workers, using a system that monitors the command devices and triggers them to do the right task at the right time. This makes it reasonable to modernize your process with automation in tandem with safety.
Often times, automation projects are executed as a part of a safety initiative. It makes both logistical and economic sense to do both at once. In many cases, the best way to minimize risk is to remove the human altogether, a process of engineering out the risky interaction. Then, the new process, which doesn’t have an operator, doesn’t have to balance operator safety with productivity.
Removing the worker from a hazardous situation means that he can focus on the value-added tasks that machines can’t get right. This might be a path to more responsibility, overseeing an end-to-end process rather than just contributing to one small part of a process.
“It’s Just a Saw”
“It’s just a saw” is a common refrain that comes up during risk assessments. Sure, it’s just a saw, but it’s a machine that has several inherent risks. Some workplaces even accept more risk than is necessary. One inquiry about purchasing a heavier-duty leather apron for a full-time abrasive saw operator led to an informal safety review. The reason for this inquiry had to do with a constant shower of sparks that caused the apron to wear out quickly. After more questioning, it became clear the three-phase motor was running backwards, causing the sparks and debris to be expelled toward the operator.
This is just one example—and hopefully the only instance of this—in which folks can be conditioned to tolerate working conditions that were never intended. A walk around any metalworking facility with a critical eye might reveal similar, if less egregious, examples of the mitigatable risks.
Identifying and mitigating risk is in the domain of the shop’s executive team, and it often leads to changes. Changing a process, whether it’s a matter of updating practices or upgrading equipment, can be overwhelming to some workers. Resistance is a common reaction. It is important to take this into consideration when rolling out anything new, whether it’s a small change to a practice, a big change in equipment, or a brand-new safety campaign.
It’s up to the executive team to take ownership of the facilities, equipment, and processes so they are run as efficiently as possible while using best practices for safety. In other words, buying a fancy system will not solve fundamental problems in a shop’s culture. A savvy safety leader can use the “It’s just a saw” reaction as an opportunity to discuss the company’s culture. It can be the engine for growth to a culture that emphasizes safety first and efficiency second.
Taking ownership of outdated practices, executing a risk assessment, and building a culture of safety are steps in a proven path to minimize risk. Considering safety when purchasing new equipment can reveal innovative solutions, including automated ones, that will reduce risk while maintaining or improving productivity. Developing a functionally safer operation may have a higher up-front cost, but it will lead to lower costs in the future through reduced worker risk, higher productivity, and the ability to hire less-experienced workers.
About the Author
Charles Vosmik
3601 Larchmont N.E.
Warren, OH 44483
330-372-3700
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