Page 28 - OHS, September 2022

MACHINE GUARDING
How much risk abatement one is striving for will dictate the level of design complexity.
Next are the human interactions with the machine, which involve the operators and maintenance personnel. With the operator, it is best to observe the different aspects of the job. We like to call this process a Design Facilitation, as it mimics some Lean Manufacturing Kaizen principles. It is essential to observe normal production runs, setups and teardowns and the potential production stoppages. Those interactions could include tool changes or even machine issues that cause stoppages and operator interactions. Machine repairs or high-risk opportunities typical can be identified here. Verify the operator to machine interactions, especially for high-risk tasks that involve rotating hardware against a fixed object as those scenarios could lead to serious injury or death.
One of the more dangerous situations is often non-production related tasks, for example, when maintenance access is required. These situations typically involve more risk and danger, so it’s important to capture these scenarios. These situations may cause additional safety features or interlocks that prevent or eliminate high risk exposure.
Another dangerous interaction is the machine loading for setup or production change over. This could involve an overhead crane, fork truck or be manually loaded. Regardless, it is important to witness and observe variations. Ultimately, we want the guard to protect them without impeding on any aspects of their job. Ideally, the design of the guard would address areas of concerns that make their job easier. Thus, the key outcome of the assessment process for guarding older machinery.
Design
Now that you have assessed the machine usage variations and human interactions, we want to move into the design characteristics. On older machines, we like to break them down into two buckets: mechanical guarding and electronic/electric interlocking.
The mechanical aspects of guarding can be summarized by restricting access over, under and through. The operator should not be able to reach through the guard. In expanded metal applications, understanding finger, hand and arm safety rated materials are critical in material selection. Metal guards are good for heat and harsh environments. But in some cases, there are risks of catastrophic failures where a tool or part could shatter. In those cases, we recommend polycarbonate/lexan guards.
One may notice that the guarding design eliminates the operator from reaching the machine. In most cases they do need access to the machine, but if regular access is required, you may need to design guard with vertical lifting or horizontal swing
doors. Next, begin asking questions, such as does the guard need to have multiple sections or access points? Are there side access panels for setting up, tearing down or changing tools? In some cases, we have seen three to four access points on a single piece of machine guarding. ThThe mechanical guard itself is a solution, but there is still risk, as the hazard is not entirely engineered out. Administrative control must be put in place, and overall safety is still determined by human factors. This may not be acceptable for you or your organization. Thus, we transition into electronic and electrical interlocking systems to mistake proof hazardous situations.
There are several interlock options to consider. First, older machines are typically wired for relay logic, which is standard relay, contactor and switch controls at 120Vac. Some just want to sustain that logic and use 120Vac rocker switches. Typically, they can be double switched and put in-line with the existing start/ stop/e-stop circuitry. Although pricing is usually better, there are two concerns with the 120Vac Relay logic. First, the switches can easily be bypassed or tied off. Secondly, having a 120Vac switch on a movable guard, that is handle by the operator, increases risk of electric shock. Thus, we recommend using RFID 24Vdc interlocks.
Radio-frequency identification (RFID) switches are anti- tamper coded safety switches. RFID switches cannot be tied back or have a magnet or metal placed on them to bypass. They are uniquely coded so that the receiver is the only trigger for the switch. With RFIDs, there is no physical contact with the switch making them non-contact safety switches. Now that the switches are 24Vdc, an enclosure with a DC power supply and safety relays are required to convert to the machines 120Vac relay logic. Once DC power is introduced to the machine, this opens the door for electronic safety enhancements.
Regarding a recent VTL OSHA abatement, it was demanded that the guard remains in place and locked until the table comes to a complete stop. As a result, custom designed electronics were developed. The components included safety rated PLCs, lockable keyed solenoids for all moving guards and sensors for table Revolutions Per Minute detection. The custom code written to obtain a total safety electro-mechanical system can be challenging. It is imperative that the machine schematics are reviewed by a professional to make sure system enhancements are integrated correctly. In some cases, the schematics do not exist and should be reviewed by an electrical engineer and/or Certified Machinery Safety Expert.
Conclusion
It is essential to assess the machines usage, human interactions and changeover risks when trying to enhance guarding on older machines. How much risk abatement one is striving for will dictate the level of design complexity. It may be outside of the organizations technical capabilities if an advanced safety system is required. Thus, a proper make/buy decision may need to be completed upfront. There are many machine guarding experts that can properly guide one through this process thus reducing overall costs and time to compliance. Understanding this process will enhance one’s abilities to properly guard older machines.
Joseph P. Gasparino Jr. is the Founder of Odiz Safety LLC.
24 Occupational Health & Safety | SEPTEMBER 2022 www.ohsonline.com