ROSS Controls & Concern for Machine Safety

A Global Snapshot of Fluid Power & Safety

Critical-application safety valves are functionally redundant, self-monitoring, and return to a safe position. It is easy to say that “Safety is everyone’s goal,” but what is really meant by that? Sound workplace safety practises can reduce the risk of injury to not only machine operators but to other people such as maintenance technicians; it can also reduce the risk that there is accidently damage to machinery and other company assets, or harm to the environment. Common industry standards acknowledge that there is no such thing as zero risk, while nonetheless providing guidance to machine builders and operators regarding how to take steps to minimise risks. This is commonly referred to as a machine safeguarding. Here’s a snapshot look at some key factors:

• Alternative Lock-out

  The ANSI/ASSE Z244.1 – 2003 (R2008) standard also addresses other lockout techniques, called alternative methods of controls. These systems can save costs and improve machine up time. But alternative methods controls only apply to routine, repetitive tasks that are integral to the production process and are based on risk assessment providing effective personal protection. The machine must still have a standard lockout system for repairs and other tasks.
  
  Alternative methods of controls offer two-time saving advantages. First, it uses a single lock-point (a remote, low-voltage system) that simplifies and speeds lockout, and enhances safety by avoiding the chance of a point being missed. The operator need not travel all around the machine to access various points to lockout or unlock operations. These systems place electrical lockout switches, connected to the control system, at locations that require machine access, and incorporate appropriate safety valves for pneumatic and hydraulic lockout.
  
  The second feature of alternative lockout systems is not all energy needs to be removed. In fact, sometimes removing all the energy creates a more-hazardous condition. This can result in significant time and cost savings when systems contain large volumes of compressed air.
  
  The standard is also useful for tasks that are not routine, repetitive, or integral to production, but require power for, say, troubleshooting a control circuit. The new standard recognizes that there is no such thing as zero risk, and that some risk is present in order to perform certain tasks. In this case, the standard requires that the control system and valve controlling the non-isolated energy be control-reliable, Category-3 or -4.

• Risk Reduction

  There is no such thing as “zero risk”. Therefore, the standards require that you assess all possible risks, and determine what possible ways can be accomplished for most-effectively reducing those risks. The best approach to risk assessment is as a team. One big change ANSI B11.TR3-2000 brought about is that both the machine manufacturer and user are responsible for performing the assessment for new and rebuilt machines. In the past, machine safety was considered the user’s responsibility. Perhaps the most difficult part is defining the subjective words for the assessment. There are no precise answers, and even the standards differ. Users need to develop their own risk assessment programme.
  
  Many companies hold that there are two degrees of injury: minor and major. Minor injuries can be treated with a first aid kit, and anything requiring more extensive care is considered a major injury for risk assessment purposes. When a company uses a risk matrix that leans toward the “better-to-be-safe” side, the first question is, of course, “Will it entail additional expense to eliminate a rare possibility?” But to error on the high side forces the assessment team to look more carefully at each hazard. Often, safety can pay back in machine up time, reduced employee absenteeism, saving the time and cost to investigate an accident, insurance savings, and other hidden costs involved with accidents. Safety is part of a company’s loss-prevention programme.
  
  Avoiding using the wrong category valve should be the primary concern when performing a risk assessment. For example, a circuit with a single valve that suffers a broken spring or a sticky spool would have a different fault result than a similar circuit employing a double valve experiencing a broken spring or sticky valve. ANSI B11.TR3-2000 sets the recommended minimum level of control integrity as follows.
  
  

  • Highest degree of risk reduction - Control systems having redundancy with continuous self-checking to ensure continuous performance.
  • High/intermediate risk reduction - Control systems having redundancy with self-checking upon startup.
  • Low/intermediate risk reduction - Control systems having redundancy that may be manually checked.
  • Lowest degree of risk reduction - Hydraulic or pneumatic devices and associated control system using single-channel configuration.

• Path to Safety

  The path to fluid power safety can be taken with these 6 steps:
  
  

  1. Identifying tasks and hazards using a Risk Assessment with fluid power considerations.
  2. Classify these hazards into categories from slight to serious, seldom to frequent, and possible to less possible.
  3. Reduce the risk by a Risk Reduction Hierarchy from Preferred to Fifth.
  4. Select the appropriate controls for safeguarding.
  5. Assess the Residual Risk.
  6. Record actions taken, monitor results, and document.

• Safety Circut Examples

  • Cylinder hazard in 2 directions
  • Pinch Points
  • Tooling or product damage
  • Single Point Lock Out
  • Press clutch/brake
  • Counterbalance
  • Monitored power systems
  • Partial de-energization
  • Vertical loads
  • Cylinder mid-stroke positioning
  • Two-hand control
  • Energy Isolation
  • EEZ-ON gradual pressure build-up
  • Noise reduction
  • 2-hand anti-tie-down machine start
  • Hose and/or fitting failure

Additional Resources:
Ross EUROPA Offers and expanded technical reference book "Fluid Power Safety for Machine Guarding", and a course in Fluid Power Safety, "TOTAL MACHINE SAFETY".

Design Standards and Certifications:
ROSS valves for Safety-related applications are designed to meet many Global standards including the following: CSA, Australian AS, EN, ISO, OSHA, ANSI, & CE

When required, ROSS products can be tested and certified by the following authorities: UL, CSA, TUV, BG