Purpose:

The purpose of this page is to describe the three categories of Emergency Stop functions and provide resources for further information about machinery safety and best practices.

Scope:

The scope of this document is to identify the three Emergency Stop function categories for discussion purposes.

The three standards that govern emergency stop categories are:

  1. ISO 13850: This standard outlines the principles for designing emergency stop functions in machinery. It ensures that operators can halt machine operations safely and efficiently during emergencies[1].
  2. IEC 60204-1: This standard specifies the general requirements for the electrical equipment of machines, including emergency stop functions. It defines how machines should behave during an emergency stop[2].
  3. NFPA 79: This standard provides the electrical requirements for industrial machinery, including guidelines for emergency stop functions. It ensures that machinery halts according to a defined and safe procedure[2].

These standards are harmonized, meaning their definitions for stop categories are essentially the same.

The stop categories are: (Note: The complexity, and subsequent costs involved, of each category grows from 0 to 1, and again from 1 to 2.)

  • Category 0: Immediate removal of power to actuators, leading to an uncontrolled stop.
  • Category 1: Controlled stop by maintaining power to the actuators until the machine has stopped, then cutting off the power.
  • Category 2: Controlled stop by maintaining power to the actuators[3].

These categories help ensure machinery stops safely during emergencies, minimizing risks and hazards.

Detailed summary of ISO 13850:

ISO 13850:2015 outlines the principles for designing emergency stop functions on machinery to ensure safety. Here are the key points:

  1. Functional Requirements: The standard specifies the functional requirements for emergency stop functions, which must be independent of the type of energy used to power the machine[1].
  2. Design Principles: It provides guidelines for designing emergency stop devices, such as pushbuttons, wires, ropes, handles, or foot pedals, ensuring they can be activated quickly and easily by a single human action[2].
  3. Activation and Reset: Once activated, the emergency stop function must halt the machinery immediately and prevent it from restarting until the function is manually reset[2].
  4. Exclusions: The standard does not cover functions like motion reversal, emission deflection, shielding, braking, or disconnecting, which can be part of the emergency stop function but are not the primary focus[1].
  5. Applicability: It applies to all machines except those where an emergency stop would not reduce risk, such as hand-held or hand-operated machines[1].

This standard helps ensure that emergency stop functions are effective in preventing accidents and injuries by providing clear guidelines for their design and implementation.


References

[1] ISO 13850:2015 - Safety of machinery — Emergency stop function ...

[2] Safety of Machinery – Emergency Stop Function - The ANSI Blog

[3] ISO13850 | USA - IDEC


References

[1] ISO 13850 Emergency Stop Function Ensuring Safety in Machinery

[2] Emergency Stop Categories - Machinery Safety 101

[3] What are the 3 stop categories according to EN60204-1?

The following is a summary of the ANSI/ISO 12100:2012 Safety Standard: (Chaotic Solutions recommends that client acquire a copy of this standard.)

ANSI/ISO 12100:2012 is a standard that provides general principles for the design of machinery to ensure safety. It focuses on risk assessment and risk reduction throughout the machine's lifecycle. Here are the key points:

  1. Terminology and Principles: The standard defines basic terminology and principles for achieving safety in machinery design[1].
  2. Risk Assessment: It outlines a systematic process for identifying hazards, evaluating risks, and determining the necessary measures to reduce those risks[1]. This includes considering all phases of the machine's lifecycle, from design and installation to operation and decommissioning[2].
  3. Risk Reduction: The standard provides guidelines for eliminating hazards or reducing risks to an acceptable level through design and protective measures[1].
  4. Documentation and Verification: It emphasizes the importance of documenting the risk assessment and risk reduction process and verifying that the measures taken are effective[1].
  5. Basis for Other Standards: ANSI/ISO 12100:2012 serves as a foundation for developing more specific safety standards (Type-B or Type-C standards) for particular types of machinery or safety aspects[2].

This standard helps designers create safer machinery by systematically addressing potential hazards and implementing effective risk reduction strategies. If you have any specific questions about this standard or need more details, feel free to ask!

References

[1] ANSI/ISO 12100:2012—Machine Safety Risk Assessments (Recommend that client has on hand a copy of this standard.)

[2] Risk assessment and risk reduction - ANSI Webstore

[3] EN ISO 12100 and its relation to the Machinery Directive - CEN-CENELEC

Procedure:

The initial configuration of a system can fall under Category 0. Effectively Category 0’s implementation will result in immediate shut-down of equipment in the event of an Emergency Stop action.

This can have unintended consequences, though. It is recommended that a risk assessment be performed for the following:

  1. Hazards to personnel: (Examples)
    1. Is removing power, and immediately shutting down drives sufficient to contain energy, both kinetic and potential forces to protect personnel in all circumstances?
    2. What are the unintended consequences of performing step a. above?
    3. Will a motor that remains energized, controlled to a stopped rotation, protect personnel in all cases?
      1. As that motor is brought to a controlled stop, does an electrical hazard remain, and for how long?
  2. Hazards to equipment:
    1. Will a Category 0 function limit hazards to equipment?

Conceptual:

It is recommended that a risk assessment be performed from the plant level down to each cell of operation to help identify areas where risks to personnel can be minimized. Risks to machinery can be kept to a minimum, assuming risks to personnel remain at a minimum. Personnel well-being is first and foremost. Equipment risk should take a backseat to safety of personnel.

Conclusion:

Chaotic Solutions can help in the risk assessment of the operations of a system. Ultimate responsibilities lie with the company that owns and operates the machinery.

The authority for accepting the category level and risk assessment typically falls to the Authorizing Official (AO) or a similar role, such as a Safety Manager or Risk Manager. This individual is responsible for ensuring that all identified risks are adequately assessed and that appropriate measures are in place to mitigate those risks[1].

The AO or Safety Manager works closely with various departments, including engineering, operations, and compliance, to ensure that the risk assessment process aligns with industry standards and regulatory requirements[2]. They also have the final say in approving the risk assessment and the associated safety measures before implementation[3].


References

[1] Risk Management Framework (RMF) and Authority to Operate (ATO) - DTIC

[2] Understanding risk assessment practices at manufacturing companies

[3] Manufacturing Readiness Assessments | www.dau.edu