Why do we need Safety Standards? For years, standards and safety have been developed and adjusted as time went on. Everyone at some point is careless, complacent, overconfident, distracted or fatigued. We sometimes take risks or misunderstand things. Because all of these human traits are ingrained in all of us, we need to make sure machines are safe and ready for use – which means we also need to consider processes which govern how we utilize machines in order to prevent accidents and injury.[i]
With the increasing use of automation, the requirements governing protection of machinery have changed and evolved. Technology advancements have allowed for the integration of protection devices into the work process, thus improving safety and productivity.
Safety is a basic need – the objective for safety equipment and safety standards is to provide the machine operator, personnel and others a safe environment when working with machinery. Managers are responsible for the safety of their employees. Most accidents are due to human error, which is why safety procedures need to start at the executive level and be adopted throughout the entire organization.[i]
In this article we’ll cover safety functions of Pneumatic technology, as covered by ASCO at Steiner’s 2016 Automation Technology Summer Symposium.
The first steps are taken by the machine operator and OEM to analyze the possible risks that are associated with the design of a machine. The risk assessment and analysis gives information that is required for the risk evaluation. This allows the operator or OEM to determine ultimately whether or not a risk reduction is required.[ii]
The process of risk reduction allows for the OEM to eliminate the potential risk that is found in the assessment. If the areas of risk cannot be eliminated, they are to be addressed with safety-related components.
A risk graph provides guidance when looking at the safety risk and safety function. The graph should be considered for each Safety Function identified as part of the risk assessment and risk reduction process.
Safety System Architectures and Categories
There are three architectures of elements – The Input Element, the Logic element and the Output element. The Input element includes Gate Switches and Light Curtains; the Logic element includes Safety PLC and Safety Relays and the Output element includes valves and motors.[ii]
There are four categories – Category 1, Category 2, Category 3 and Category 4. Category 1 systems rely on reliability data of components or well-tried components. With Category 1 there is no diagnostic monitoring.
Category 2 systems rely on Category 1 data plus feedback monitoring and periodic testing of safety functions. Category 3 systems rely on Category 2 data plus redundancy. In Category 3 safety systems, most faults are detected. Category 4 systems rely on Category 3 data plus greater diagnostic monitoring – in which all faults are detected.[ii]
Methods of Pneumatic Implementation
There are three main methods of satisfying a pneumatic Safety Function, including: Discrete components, Point-of-use “Dump” style units, and Manifolds with integrated Safety Functionality.[ii]
Discrete components have individual valves and pressure switches. Switches are limited to a single motion and can be used for multiple motion elements or actuators. These discrete components can be adapted to various pneumatic safety functions. Discrete pneumatic components are best used on single axis or individual motion elements in order to satisfy a pneumatic safety function. The pneumatic components are considered Safety Related Parts of a Control System.
Point of use “Dump” style units are individual assemblies that are made of redundant units to provide safe release of energy in the form of air. These are best used on Lock-Out Tag-Out (LOTO) applications. These type of units can be used to release or “Dump” the pneumatic energy to a gated machine in most instances.[ii]
Finally, manifolds with integrated safety functionality are manifolds that have the ability to satisfy many pneumatic safety functions while providing that function for multiple motion elements, or actuators. These Manifolds are best applied for the following:
- Multiple axis of motion (actuators)
- Requires Safe and Non-Safe Valves or motion
- Requires additional pneumatic features such as regulation, speed control or circuit manipulation
- Requires different safety functions on the same manifold
- Requires a Fieldbus interface
- Safety functions are defined by the Risk Assessment or Reduction Process.
- Machine Safety is a systematic approach
- A Pneumatic safety function doesn’t always need to trap energy – there is a safe stopping of motion and a safe return to the home position
- Indirect monitoring or pressure sensing, can provide the highest level of direct current
Protective devices should be integrated into the control system. Control systems are made of input elements, logic units and power control elements in addition to the actuator or work element. Safety-related parts of the control system should safely perform normal functions. Because of this, special requirements are placed on their reliability and resistance to failures. Safety standards and devices allow for an increase in the attempt to prevent injury. Because all humans can be careless, forgetful or distracted, it is important to implement and follow standards and procedures.
For more information on automation safety and to speak with one of our application engineers please call 1-800-STEINER (783-4637).
[i] Guidelines for Safe Machinery – Six Steps to a Safe Machine. N.p.: SICK Sensor Intelligence, n.d. PDF.
[ii] Machine Safety and the Integration of Pneumatic Technology. N.p.: ASCO Emerson, 2016. PPT.