Addressing electrical safety hazards
Considering newer products and technologies can improve personnel safety, especially when combined with a “design for safety” approach and appropriate automation.
Electrical safety insights
Electrical safety has improved thanks to more awareness and adherence to standards, but more improvements can be made thanks to new technologies and increased emphasis on design.
Access control and absence of voltage testing (AVT) are two growing trends in electrical safety and can keep workers safe from arc flash or other electrical safety hazards.
In many industrial plants and facilities and some commercial facilities, the mitigation of electrical shock and arc flash hazards are top-of-mind issues for protecting people and property as well as regulatory compliance. These types of safety issues impact all types of operations and not just the largest industrial sites. Small manufacturers and commercial operations such as data centers all need to address potential electrical hazards.
There is a lot of relevant information available regarding application and governance of safety provisions, ranging from laws, to standards, to best practices. The expectation is each workplace establishes evolving policies, procedures and program controls to mitigate worker risk to an acceptable level. This practice is often referred to as an electrical safety program.
Most companies invest in and specify technologies for mitigating risks and controlling hazard exposures. These are guided by well understood methodologies, such as the National Institute for Occupational Safety and Health Hierarchy of Controls. In support of these best practices, this article identifies how some newer products and/or the addition of automation, can increase the effectiveness of safety controls.
Performance and prescription for electrical safety
The Electrical Safety Foundation International collects data from the U.S. Bureau of Labor Statistics to publish the Workplace Electrical Injury & Fatality Statistics. From 1992 to 2010, there has been a significant reduction in electrical injuries — more than 50% — which can be attributed in part to the application of new technologies and best practices, which have reduced risk and exposure to electrical hazards. However, this positive trend is tempered because the number of nonfatal electrical injuries flattened to an average of about 5 per day from 2010 to 2020 (around 2,000 per year).
It seems electrical safety advances have reached a point of equilibrium with respect to results. However, there is still room for new technologies, along with an emphasis on improved designs and practices, to further reduce the frequency of electrical injuries (Figure 1).
Electrical safety and lockout/tagout are governed by two main requirements determining the “what” and the “how” of these systems. The Occupational Safety and Health Administration provides performance-based workplace requirements (the “what”), such as 1910.147 The Control of Hazardous Energy (Lockout/Tagout). NFPA 70E: Standard for Electrical Safety in the Workplace explains the prescriptive-based requirements (the “how”). Quoting from the NFPA 70E fact sheet document:
“NFPA 70E fleshes out how the performance-based requirements in the OSHA standards can be met by providing and defining minimum standard industry practices necessary for electrical safety. OSHA is the law and NFPA 70E outlines ways to comply with OSHA’s electrical safety requirements. This symbiotic relationship between NFPA 70E and OSHA electrical safety standards helps to increase safety in the workplace.”
A theory called the Rogers Adoption Curve models and categorizes how new innovations and technology move from introduction to widespread use. Observing companies and organizations that are innovators and early adopters provides a roadmap of where one would expect new technologies to be introduced and propagated for widespread future deployment. The strength of an electrical safety culture varies throughout commercial and industrial sectors and how proactive an organization is in general is often an indicator of how willing they are to adopt newer safety technology.
Two electrical safety technology trends
With this in mind, there are many evolving trends and technologies proactive companies should consider and apply to improve electrical safety by mitigating worker exposure to electrical hazards.
One growing safety trend is to limit worker access to potentially hazardous locations by means of intelligently-designed manufacturing cells, power distribution enclosures and equipment and control enclosures. Permission to access these and other types of protected locations can be controlled by one or more factors:
Worker credentials based on training and skills.
Confirmation of a worker wearing specific personal protective equipment.
Condition of the equipment and whether it is in a safe/de-energized state.
The most basic access control programs are procedural. Users adhere to company requirements for equipment access or perhaps are issued a physical access control key when they are trained to perform the work properly and safely.
However, innovators and early adopters within several industrial and commercial vertical markets are deploying more advanced access control based on technology, networking and automation (Figure 2). The driving factors for these approaches are to improve risk mitigation, efficiency and speed.
A typical use case would be the design of a manufacturing cell with enclosed electrical equipment. The cell is normally locked from operator use while energy (electrical, pneumatic and/or other) is present. However, the interior of the cell can be accessed by electricians with the proper training, PPE and tools. A system of sensors and controls is deployed to accomplish the cell locking/unlocking task. One way to do this is by providing a pushbutton so the qualified operator can request entry to the cell. Upon detecting a button push, an automatic safety system will move the equipment to a safe position and de-energize electrical, pneumatic and other power sources. Once the equipment is verified as safe using appropriate sensors, the entry gate is unlocked. Existing standards provide guidance for these types of applications.
IEC 61508 is a standard defining safety integrity levels, along with methods of applying, designing, deploying and maintaining automatic safety-related systems. ISO 13849 is a safety standard providing requirements and guidance for control systems design.
There are many sensing devices and controllers to help ensure operators are only allowed to approach equipment when it is safe and the equipment is driven to a safe state if any condition is breached (Figure 3). The most common are:
Safety switches, edges and bumpers, which detect if hardware is moved to open the cell or if an operator is approaching the protected area
Interlock safety switches and trapped key interlock switches holds hardware closed if the cell is not safe and releases hardware if the cell is safe
Emergency stop buttons and cable-pull safety switches, which allow operators to trigger the emergency stop circuit
Safety light curtains and safety laser scanners allow safety automation systems to detect if people are moving into a cell through an open space
Two-hand controls and safety enabling switches helps ensure operators are in a safe location before a cell is energized
Safety relays and safety controllers are used in conjunction with sensors and other devices to disable power to a cell or equipment, putting it into a safe state when necessary.
Absence of voltage tester
An example of recent innovation in the electrical safety arena is recognition in the 2018 edition of NFPA 70E of a new technology option for verifying the absence of voltage within electrical equipment. Electrical equipment is often provided with a disconnecting means. To verify the equipment is de-energized, the user must wear proper PPE while performing a live-dead-live test. This means using a voltmeter to first test a known live circuit (verifying the meter is functioning correctly), then using it to check the circuit to be worked on is dead and retesting once more on the known live circuit (verifying the meter is still functioning).
Absence of voltage testers is a new category that has been developed and incorporated into the NFPA 70E. Some versions of this device are available with SIL3 safety-rated contacts, much like a safety controller or relay, so they can be integrated with other controllers and devices. This approach provides an automated method to enable an enclosure to be unlocked when an absence of voltage is confirmed. Devices and technologies like AVTs are making it easier to automate safety, while improving the efficiency and performance of safety systems.
Design for safety
Many daily experiences have been changed over the last few years through the application of technology to mitigate risk and automate repetitive tasks. For example, backup automobile cameras used to be an expensive and rare technology, but now they are common and are an additional tool along with rear-view mirrors to improve rearward visibility. Intelligent robotics — some able to work collaboratively side-by-side with humans — are able to perform repetitive or hazardous manufacturing or assembly tasks where in the past human workers may have experienced monotony leading to carelessness and injury.
Similarly, designers and end users should also be open and innovative with respect to opportunities for automating lockout/tagout and other tasks that have been manual- or procedural-based for decades.
Adding safety features and leveraging technology up front — following a “design for safety” approach — not only mitigates the exposure of workers to hazards, but in many cases increases efficiency and throughput.
Original content can be found at Plant Engineering.