What Benefits Safety Devices Can Offer and How to Utilize Effectively

Q&A: What Benefits Safety Devices Can Offer and How to Utilize Effectively

Safety devices are essential in the industrial workplace to separate people from dangerous zones; they are a tried and true way to reduce risk and injury. While placing a safety barrier around a dangerous space may seem like a straightforward topic, many nuances come with various barrier types that deserve a more in-depth look.

Learn more about safety devices and commonly asked questions in our Q&A below.

Q: What should be considered when implementing machine safety?

There are six foundational steps for implementing machine safety correctly: risk assessment, safe design, controls of the safety function, administrative measures, overall validation, and machine operation.   

Risk assessment involves defining the machine’s limits, identifying all tasks associated with the machine, and estimating and evaluating the risks. It is vital to document the entire risk assessment process. Some companies don’t have the time to do a full risk assessment on their machinery, so they bring in a third party. Consider instead using a SICK device, the experts in safety, to compile a risk assessment. SICK offers risk assessment services that create a 3D model of designs that can show all possible solutions for a machine or process at a fraction of using a third party.

It is easier to ensure a machine’s safety or process with a safe design rather than to safeguard the device through its control system. By utilizing safe design approaches that are simple to apply, such as limiting access points to entanglement areas to no more than 6 mm to eliminate pinch points or protecting against electromagnetic currents through proper grounding, the safety features are built into the machine itself. It is essential to realize that devices such as e-stops are not true safety devices, but rather the last defense line against injury.

Controls of safety functions are also a critical component in safety design. The original equipment manufacturer (OEM) and end-user must determine the “acceptable level of risk,” which serves as a crucial step in the overall safety function implementation in engineering controls. Defining the functions and the necessary safety performance level is critical to operations. In this process, designing and verifying safety functions in the machine’s mechanical, electrical, and functional aspects is necessary.

Administrative measures, such as signs and warnings, are the least effective way to minimize risk. These measures should never be viewed as replacements for the safe design and engineering controls. However, signs, warning lights, horns, or safe work procedures, like Lock-Out Tag-Out procedures, and personal protective equipment (PPE) can help get the desired result of designing a safe machine process.

Overall validation is a process that verifies the defined policies that were put into place to mitigate the risk.

End-users are ultimately responsible for machine safety. It is critical during the procurement process to: clarify the scope of the supplier safeguarding implementation provided in advance, define which additional documentation is to be supplied (i.e. a risk assessment), and define which standards apply and how they will be documented.

Q: What is the difference between Performance Level (PL) and Safety Integrity Level (SIL)?

Required and actual safety levels are determined in accordance with the risk level. Performance Level (PL) uses a risk graph according to standard EN ISO 12849-1 to determine PL. Safety Integrity Level (SIL) adopts a numerical procedure to determine SIL. SIL considers the probability of an occurrence of a hazardous event. When choosing the required performance level, both standards consider the severity of the injury, the frequency or the duration of the hazard, and the options for avoiding the hazard or limiting the injury. The result of EN ISO 13849 is a required performance level PLr a, b, c, d or e, where e corresponds to the highest risk level. The results of EN 62061 are classified in three risk levels SIL 1, 2 or 3, where 3 represents the highest risk.

Both methods check whether the remaining residual risk is acceptable. The a PFHd value is determined here as the variable measure. 

Q: Can standard sensors be used in safety functions?

There are some cases where standard sensors can be used in a safety function, it depends on the safety performance of a specific machine or process. It is not possible for standard opto-sensors to detect people during machine operation. Except for the MTFF, it is also not possible to specify further safety parameters (PL, SIL, DC, etc.) for standard sensor components. However, a high MTTF value only covers a small part of the criteria and measures required during a risk assessment. Recommendations for applying standard sensors in safety functions need to follow in accordance with EN ISO 13849-1.

Q: How can I calculate the safety distance required and what factors play a role in the equation?  

The minimum safety distance describes the minimum distance between the protective device and the hazardous area. The required minimum safety distance is calculated according to the standard EN ISO 13 855. The general formula for calculating the minimum safety distance is:

S = (K x T) + C

•    S is the minimum distance in millimeters, measured at the next hazardous point to the detection point and/or detection line or detection plane of the protective device.

•    K is a parameter in millimeters per second, derived from the data for the approach speeds of the body or parts of the body

.•    T is the stopping/run-down time of the overall system in seconds.

•    C is an additional distance in millimeters. The distance C depends on the application (see Table 1 in the standard EN ISO 13 855)

Q: What benefits do safety scanners and light curtains offer?

The advantage of using an optical device like a deTec4 light curtain for point-of-operation protection is that it allows for a short minimum distance, and the operator can work more ergonomically (for example, during loading work on a press). The resolution of the beams can be set small enough to detect a hand or even one finger. This allows the safety system to respond quickly when the sensor is tripped.

In hazard area protection, the person’s approach is detected by sensing the person’s presence in an area. Area protection is necessary for machines whose hazard area cannot be viewed entirely from the reset device’s position. If the hazard area is entered, a stop signal is initiated - stopping the machine and preventing restart. Hazard area protection is also essential for automated guided vehicles (AGVs), or cranes to protect people while the vehicles are in motion or docking to a fixed machine.

The safety laser scanner monitors hazardous areas of machines by scanning its surroundings in two dimensions using an infrared laser beam. It works on the time-of-flight principle, which measures the time it takes for a light pulse to travel between the scanner and an object to calculate its distance. As soon as the safety laser scanner detects an object or person in the protective field, a safe machine shutdown is initiated. Warning fields can detect an intrusion before the actual hazardous area, signaling an audible or visual alert, or machine slowdown.

Using a safety laser scanner like the microScan3 from SICK will create a fenceless safety solution for a machine or process. Hard guards or mechanical fences limit access to machines and make changeovers more complicated and time-consuming. Physical barriers occupy valuable real-estate on the shop floor that could be used for value-added processes. Safety mats, light curtains, and other perimeter guarding also consume extra space for installation and the required safe stopping distances. Fenceless safety is a non-contact solution, saving floor space and improving access to machines for the quick changeover.

Both the light curtains and safety scanners from SICK have solutions for washdown and ATEX environments; they can also be used in outdoor applications. An additional feature light curtains and safety scanners have is the ability to solve entry/exit applications when doors cannot cover access points or hard guarding, which makes muting critical. Muting is used to temporarily deactivate the protective function of a device where sensors, or other logic, is built into the system to acknowledge when to mute and return to full safety operation.

Q: How can I tell when a safety event occurs?

SICK offers an event camera that can be used with a safety scanner that not only stops the machine safely but will take photos and video when a person or object breaks a field set. This allows for detection of what happened to cause the safety event – was it an operating error of did something else occur within the machine?

There is also the capability to use the microScan3 as visualization software for a human-machine interface (HMI) that gives the ability to see where the object broke into the field set in the area of the field. Using the graphic scan and providing the location of where the field set was broke can give insight into when and why a safety event occurs.   

Q: What is fault masking?

Fault masking is an event in which one defect prevents the detection of another. It is a dangerous condition in safety circuits resulting from daisy chaining multiple safety devices in a safety circuit. Fault masking can occur when a series connection of switches with volt-free contacts are included in a series of magnetic safety switches, electromechanical safety switches, or safety locking devices. Due to the series connection, fault recognition in the evaluation unit could be reset by operating other safety switches.

The actual fault then becomes hidden, and the interlocking circuit can be released.In this situation, the fault mask can let dangerous machine functions continue even though there is a fault in the interlocking circuit.  If faults accumulate, the safety function is lost.

The risk of possible fault masking in the conventional series connection of safety switches or emergency e-stops limits the safety performance. There are two primary solutions to avoid fault masking: (1) using safety switches with monitored outputs, and (2) utilizing a safe sensor cascade to monitor sensors and wiring for faults continuously. SICK’s TR4 Safety Switches with monitored outputs, or the Flexi Loop Safe Sensor cascade is an excellent solution for fault masking applications.

Q: Where do I start if I want a Risk Assessment for my machine or process?

Barr-Thorp Electric has a partnership with SICK’s dedicated safety experts. Together, we can evaluate existing design or turn-key solutions to ensure safety standards and productivity needs are met. Using SICK’s systematic approach to safeguarding, we offer consulting and design services like risk assessments and verification safety services. During a risk assessment, a SICK TUV Certified Safety Applications Engineer will evaluate the hazards at each operation task and provide a report that documents the performance level required and category compliance with industry standards. The information includes a mitigation plan in the case of compliance gaps.

We will then use the Machine Guard Risk Assessment output to create a safe design that will include proper component selection, electrical design, and tie-in to existing circuitry, software design, and mechanical perimeter fencing and point-of-operation guarding. The details of the project will be documented in a comprehensive report package including electrical schematics, a bill of materials, solution layout for liability records, and integration and go-live support. Installation, commissioning, and integration can be supported by SICK or a contractor of your choice.

Bring in the experts from Barr-Thorp in at the beginning of a project. We can assist you with specific design elements or turn-key solutions that will save you time and money and ensure you are utilizing the latest technologies to maximize performance and ensure compliance with the latest safety standards.

Barr-Thorp Electric Company can provide a solution for your safety needs by creating a customized application using safety vision equipment. To learn more, contact Barr-Thorp at 800-473-9123.