Safeguarding Industrial Operations: An Introduction To Interlocked Guards

interlocked guard on a machine

In today's fast-paced industrial landscape, ensuring the safety and efficiency of operations is paramount. One crucial aspect of achieving this goal is the implementation of interlocked guards. These sophisticated safety systems play a vital role in safeguarding workers and machinery, while also optimizing productivity.

This article delves into the world of interlocked guards, exploring their functionality, benefits, and the significant role they play in enhancing workplace safety and efficiency. By employing interlocked guards, organizations can create a secure environment that minimizes the risk of accidents and promotes seamless operations.

What Are Interlocked Guards?

Interlocked guards are a type of machine guard. They have sophisticated safety systems designed to protect workers and machinery in industrial environments. They are physical barriers equipped with mechanisms that prevent access to hazardous areas or the activation of machinery until specific conditions are met. They function based on the principle of interlocking, which means that the guards are interconnected with the machinery or equipment they are protecting. The purpose of these guards is to create a safe working environment by minimizing the risk of accidents and injuries, ensuring that operations are conducted only under controlled and safe conditions. Below are the different types of interlocked guards, their applications, and benefits.

4 Types of Interlocked Guards

  • Physical Interlocks: Physical interlocks utilize physical barriers such as doors, gates, or panels to restrict access to hazardous areas. They are equipped with interlocking mechanisms that prevent the removal or bypassing of the guard until the machinery is in a safe state.
  • Electrical Interlocks: Electrical interlocks use electrical signals to control the activation or deactivation of machinery in coordination with the position of guards. They employ sensors, switches, or relays to detect the status of the guard and the machinery and ensure proper synchronization. Common examples include safety limit switches, emergency stop buttons, or light curtains.
  • Mechanical Interlocks: Mechanical interlocks rely on mechanical mechanisms to prevent access to hazardous areas or the initiation of equipment operation. They use mechanical devices such as key interlocks, trapped key systems, or captive bolts to ensure the sequential operation of guards and machinery. Mechanical interlocks provide a physical lockout and prevent unauthorized access or tampering.
  • RFID-based Interlocks: RFID-based interlocks utilize radio frequency identification (RFID) technology to control access and ensure proper coordination between guards and machinery. They employ RFID tags or cards to enable or disable the interlocked guards based on the authorization level of individuals. These interlocks offer enhanced security and flexibility in managing access control.

Sample Applications of Interlocked Guards

Interlocked guards are widely used in manufacturing plants to protect workers from the hazards associated with heavy machinery, conveyors, and assembly lines. They also play a vital role in robotics and automation, ensuring the safety of personnel working with robots and automated systems, preventing accidental contact or collisions.

In the power industry, interlocking guards are utilized to secure access to high-voltage equipment, ensuring the safety of operators during maintenance or repairs. Interlocking guards are employed in industrial ovens and furnaces to control access, monitor temperature levels, and prevent accidents caused by heat exposure.

Benefits of Interlocked Guards

Interlocked guards offer numerous advantages in industrial environments, enhancing safety and operational efficiency while ensuring compliance with safety standards and regulations. Let's explore the key benefits:

  • Enhanced Safety Measures: Interlocking guards prevent unauthorized access to hazardous areas, reducing the potential for human error or intentional disregard of safety protocols. By interlocking guards with machinery, they ensure that equipment operates only when guards are in their proper position, mitigating the risk of accidental contact.
  • Prevention of Unauthorized Access: These guards act as physical barriers that prevent unauthorized personnel from accessing hazardous areas or coming into contact with dangerous machinery. They require specific conditions to be met before granting access, such as machinery being in a safe state or the use of authorized access cards or keys. Interlocked guards discourage tampering or bypassing of safety measures, creating a more secure work environment.
  • Increased Operational Efficiency: Interlocked guards enable seamless workflow by allowing machinery to operate only when guards are properly in place, eliminating delays caused by manual intervention or verification. They facilitate easier and quicker access to machinery during maintenance or troubleshooting, minimizing downtime and optimizing productivity. They provide a balance between safety and productivity, ensuring efficient operations without compromising on the well-being of workers.
  • Compliance with Safety Standards and Regulations: Implementing these guards demonstrates a commitment to meeting safety standards and regulatory requirements. They help organizations adhere to industry-specific guidelines, such as OSHA standards for machine guarding or ISO 14119 for interlocking devices. By ensuring compliance, businesses can avoid penalties, legal liabilities, and reputational damage associated with safety violations.

3 Components of Interlocked Guards

Interlocked guards have 3 main components which include safety sensors, interlocking devices, and a control system.

Safety sensors are vital components of interlocked guards that detect the presence or absence of personnel, objects, or hazards in the protected area. Examples include presence sensors, light curtains, pressure mats, or proximity sensors. These sensors send signals to the control system, triggering appropriate actions based on the detected conditions. Next, interlocking devices ensure the interconnection between the guards and machinery, enabling the activation or deactivation of equipment based on the status of the guards. They include devices such as safety limit switches, solenoid locks, mechanical latches, or RFID readers. Interlocking devices enforce a sequence of operations, preventing machinery from running unless the guards are properly positioned.

Lastly, the control system is the central component that receives signals from safety sensors and interlocking devices and manages the overall operation of the interlocked guards. It controls the activation and deactivation of machinery, monitors the status of guards and sensors, and provides feedback on the system's functionality. The control system may include programmable logic controllers (PLCs), relays, or safety-rated control modules.

How Do Interlocked Guards Work?

  • Sensing and Detecting Hazards: Safety sensors detect the presence of personnel, objects, or potential hazards in the protected area. They send signals to the control system, indicating the need for protective measures.
  • Activation and Deactivation of Machinery: When the safety sensors confirm a safe condition, the control system activates the machinery, allowing it to operate. If a hazardous condition is detected, the control system deactivates the machinery, preventing further operation.
  • Monitoring and Feedback Mechanisms: The control system continuously monitors the status of the guards, safety sensors, and interlocking devices. It provides real-time feedback to operators or displays warning indicators in case of any abnormalities or malfunctions.

Maintenance and Troubleshooting

Maintenance and troubleshooting play vital roles in ensuring the optimal performance of interlocked guards. To begin, regular inspection and upkeep are necessary to identify any potential issues or malfunctions, preventing unexpected breakdowns that may compromise worker safety. Establishing a maintenance schedule, outlining specific tasks and intervals, aids in the smooth operation of interlocked guards.

During maintenance, adherence to manufacturer guidelines and industry standards is crucial. Thoroughly inspecting guard components for wear, verifying alignment and adjustment, and lubricating moving parts are key steps to maintain optimal performance. By following these procedures, potential issues can be promptly addressed, ensuring the guards are functioning effectively.

In the event of troubleshooting, a systematic approach is essential. This involves careful examination of the interlocked guard system, assessing electrical connections, verifying sensor functionality, and testing the control circuit. Documenting the troubleshooting process provides valuable references for future improvements.

Common Issues and Troubleshooting Techniques

  • Sensor Failures: Check sensor connections and wiring for any loose or damaged connections. Replace faulty sensors that fail to detect hazards or provide inaccurate readings.
  • Interlock Malfunctions: Inspect interlocking devices for mechanical faults or misalignments. Verify proper installation and alignment of guards with interlocking mechanisms.
  • False Tripping: Adjust sensitivity settings of safety sensors to prevent false triggers caused by environmental factors. Review the positioning and alignment of guards to minimize unintentional activations.
  • Communication Errors: Check the communication channels between interlocking devices and the control system. Inspect wiring, connections, and programming to identify and resolve communication issues.

Regular maintenance, thorough inspections, and prompt troubleshooting are essential to ensure the reliable operation of interlocked guards, minimizing downtime and maximizing safety.

Industry Standards and Regulations for Interlocked Guards

  • OSHA Standards for Machine Guarding: OSHA (Occupational Safety and Health Administration) has specific standards (29 CFR 1910.212) that outline requirements for machine guarding, including interlocked guards. These standards mandate the use of interlocked guards to prevent contact with hazardous machine parts and specify design, construction, and installation guidelines.
  • ISO 14119: Interlocking Devices Associated with Guards: ISO 14119 is an international standard that provides guidance on the selection, design, and application of interlocking devices associated with guards. It emphasizes the importance of interlocking devices in ensuring the safety of personnel and machinery and addresses topics such as coding, mechanical, electrical, and programmable interlocking systems.
  • ANSI/PMMI B155.1: Safety Requirements for Packaging Machinery: ANSI/PMMI B155.1 is a standard specifically focused on safety requirements for packaging machinery, including interlocked guards. It provides guidelines for the design, construction, and use of interlocked guards to protect operators and prevent access to hazardous areas during packaging operations.
  • IEC 60947-5-3: Low Voltage Switchgear and Controlgear: IEC 60947-5-3 is an international standard that covers the safety of low voltage switchgear and controlgear, including interlocking devices. It specifies requirements for interlocking mechanisms used in electrical control systems to ensure safe operation and prevent accidental activations or deactivations.

Adhering to these industry standards and regulations is crucial for organizations to ensure the effective implementation of interlocked guards and maintain a safe working environment for their employees.


1. How can interlocked guards be integrated with existing machinery?
Integration of interlocking guards with existing machinery can be achieved through the following steps:

  1. Conduct a thorough risk assessment to identify hazardous areas and determine the appropriate placement of guards.
  2. Select interlocking devices that are compatible with the machinery and suitable for the identified hazards.
  3. Ensure proper installation and alignment of interlocked guards with the machinery.
  4. Connect interlocking devices to the control system of the machinery, establishing the necessary communication for activation and deactivation.

2. Are interlocked guards mandatory for regulatory compliance?
The requirement for interlocked guards depends on the specific industry and applicable regulations. However, in many cases, interlocked guards are indeed mandatory for regulatory compliance, including OSHA standards for machine guarding in the United States (29 CFR 1910.212) and ISO 14119, which provides guidance on interlocking devices associated with guards, and Industry-specific standards such as ANSI/PMMI B155.1 for packaging machinery safety.

3. Can interlocked guards be retrofitted to older machinery?
Yes, interlocking guards can often be retrofitted to older machinery to enhance safety. The process may involve:

  • Conducting a risk assessment to identify the necessary guard modifications or additions.
  • Identifying suitable interlocking devices that can be integrated with the existing machinery.
  • Ensuring compatibility between the interlocking devices and the machinery's control system.
  • Adhering to relevant industry standards and guidelines during the retrofitting process.


The material provided in this article is for general information purposes only. It is not intended to replace professional/legal advice or substitute government regulations, industry standards, or other requirements specific to any business/activity. While we made sure to provide accurate and reliable information, we make no representation that the details or sources are up-to-date, complete or remain available. Readers should consult with an industrial safety expert, qualified professional, or attorney for any specific concerns and questions.


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Author: Herbert Post

Born in the Philadelphia area and raised in Houston by a family who was predominately employed in heavy manufacturing. Herb took a liking to factory processes and later safety compliance where he has spent the last 13 years facilitating best practices and teaching updated regulations. He is married with two children and a St Bernard named Jose. Herb is a self-described compliance geek. When he isn’t studying safety reports and regulatory interpretations he enjoys racquetball and watching his favorite football team, the Dallas Cowboys.