Two-Hand Control Devices

In the realm of industrial safety, safeguarding human life and preventing workplace accidents is paramount. Among the various safety measures available, Two-Hand Control Devices (THCDs) play a pivotal role. These devices are crucial in environments where machinery operates with potential hazards. The NBR ISO 13851 Safety of machinery — Two-hand control devices — Principles for design and selection, revised in March 2024, sets forth the principles for the design and selection of these essential safety components.

Understanding Two-Hand Control Devices

A Two-Hand Control Device requires operators to use both hands to initiate and maintain the operation of machinery, ensuring that their hands are kept away from dangerous zones. This design fundamentally aims to protect the operator by making it impossible to reach into hazardous areas while the machine is in operation.

Standards and Safety Regulations (NBR ISO 13851)

The NBR ISO 13851 standard specifies the safety requirements for THCDs. It does not prescribe specific machines for their use but focuses on the general criteria needed to enhance operational safety. These devices are categorized under type B2 safety standards according to NBR ISO 12100, which covers devices requiring two-hand operation to prevent inadvertent machine activation.

Design and Selection of THCDs

Selecting the right THCD involves a detailed risk assessment, as outlined in the NBR ISO 12100. The standard distinguishes three types of THCDs, each tailored to different operational and environmental conditions:

  1. Type A: Designed for general use where synchronous hand activation is essential.
  2. Type B: Incorporates additional features such as emergency stops or enhanced feedback mechanisms.
  3. Type C: Suitable for high-risk environments, offering advanced safety features like automatic system diagnostics.

The design must ensure that the activation of the machine requires simultaneous pressing of controls, minimizing the risk of accidental start-up. This is critical not only for the safety of the operator but also for the overall operational integrity of the machinery.

Role of Two-Hand Control in Comprehensive Safety Management

Integrating THCDs into a comprehensive safety management system enhances the overall safety landscape of industrial operations. These devices work in tandem with other safety measures, such as interlocking devices and pressure-sensitive safety mats, to create a multi-layered defense against accidents. Stakeholders, including machine manufacturers, safety regulators, and operators, must understand and implement these integrated safety protocols to maintain a safe working environment.

Challenges and Considerations

Implementing THCDs is not without challenges. Key considerations include the ergonomic placement of controls to prevent fatigue and ensure comfort without compromising safety. Training for operators is also crucial to ensure they understand the functionality and importance of THCDs in their daily operations.


Two-Hand Control Devices are more than just an operational requirement; they are a critical safety measure that protects lives. Adhering to the NBR ISO 13851 standards is essential for manufacturers and operators alike, ensuring that safety is never compromised.

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