Ted Sberna Ted Sberna
Principal Owner

Use of Alternative Methods to Control Hazardous Energy—In Lieu of Lockout of Press-Related Equipment

December 28, 2021


The review and analysis for applications of alternative methods for the control of hazardous energy in lieu of lockout for press-related equipment should start with an understanding of several ANSI machine safety-standard documents.  First and foremost: ANSI/ASSP Z244.1-2016 R2020, The Control of Hazardous Energy–Lockout, Tagout and Alternative Methods.  In addition to Z244.1, we’ll discuss other ANSI B11 documents here.

Z244.1 provides the following guidance to justify the use of alternative methods, requirements detailed in various clauses of the document:

  • A practicability/justification analysis
  • A risk assessment
  • Other applicable evaluations as detailed in clauses in the standard.

This detailed documentation, along with the documentation created by following additional guidance of ANSI B11.0, B11.26, B11.19, B11.1 (or B11.2), B11.20, and others for specific equipment, provides the end-user a defendable position for the use of alternative methods for performing tasks in their stamping-related applications.

OSHA Alternative Method Overview

OSHA past interpretation recognizes that properly designed safety-control circuits can provide effective protection for control of hazardous energy when using alternative methods for tasks.  Previously accepted methodology is a safety-control circuit that meets the design requirements of the ANSI term “control-reliable” safety circuit. 

Properly designed safety-control circuits meet the requirements of a “control-reliable” circuit per ANSI B11.26. Control reliable is a minimum of a category 3 circuit architecture, an architecture or design where “no single failure will cause the loss of the safety function.” In addition, aspects of category 4 circuits regarding monitoring are an essential part of the design as well, as discussions pertaining to the requirements to achieve effective control with category 3 continue to occur, given the ability to have undetected failures that can lead to the loss of safety function.

Risk-Assessment Process

The ANSI Z244.1 subcommittee has detailed that the risk-assessment process as prescribed in ANSI B11.0 is used to determine if an acceptable risk can be achieved by applying an alternative method to complete specific tasks, instead of following the requirements for lockout to perform said tasks.

A risk-assessment document provides the steps needed to bring s piece of equipment into compliance, per the appropriate ANSI and OSHA codes.  The assessment considers all aspects of the safety system, as discussed in a previously published MetalForming article.

The risk-assessment documentation should be reviewed as part of the overall safety-system review.

Implementing the Alternative Method

The press slide/die-area space presents numerous opportunities for personnel to interact with equipment, and those tasks cannot always be completed by following OSHA 1910.147/ANSI Z244.1, hazardous-energy-control lockout methods.  Unfortunately, far too often the analogy of having the “cart before the horse” occurs as the alternative method is implemented without following the requirements noted above regarding the use of alternative methods as prescribed in Z244.1:

  • A practicability/justification analysis
  • A risk assessment
  • Other applicable evaluations as detailed in clauses in the standard.

The above documentation, along with the properly designed and validated safety-control circuit, provides the defendable information to justify not following the hazardous-energy-control lockout methods.  Only after completing this documentation and analysis should a stamper implement an alternative method.

Given that the tasks involve the press control, it also is typical that the emphasis on circuit analysis focuses on the clutch/brake or servo-drive control for the press only, without properly considering that multiple pieces of equipment, under different control systems, exist in the same shared space where operators are completing tasks.  This shared space is where ANSI B11.20, and the other B11 standards noted, provide requirements and guidance on how the various safety-control systems, and the safety-related devices, must be integrated together to provide the proper safety-circuit performance to meet the requirements of a documented task-based risk assessment.

Note: Simply placing the press (and related equipment) into a manual operating mode is not in itself an example of a properly implemented alternative method.   Manual mode, by itself, is not a safety circuit and does not prevent unexpected motion, nor can it meet the OSHA requirement of effective protection needed to justify the task being performed in lieu of lockout.  This would not meet the analysis required in a documented risk assessment for appropriate risk-reduction methods for those tasks, nor the requirements of a control circuit providing for alternative method hazardous-energy control.  The addition of some simple safety circuits can easily be provided, but without the review and planning process completed during the risk-assessment phase of a project, it becomes more costly as an afterthought and can lead to other hidden or future costs.

While a transfer press often is thought of a shared-space application, other examples include tandem-press lines with various types of press-to-press automaton, including robots; blanking-press lines with coil-feeding and stacking automation; progressive-die coil-fed press operations; and automated presses with blank-destacking/feeding equipment.  

Exclusive Control

To simplify the use of an alternative method to control all of the unexpected motion of the press and automation equipment, we suggest the use of an exclusive control device as part of a properly designed safety-control circuit. The circuit should be designed to ensure the interlock of all of the various control systems found within the shared space. Providing someone with exclusive control of the safety-control circuits for the press and related equipment ensures that no one else can reset the safety system without their knowledge, and prevents unexpected hazardous motion while that person interacts with the equipment to complete a task. Examples of an exclusive control device that can be designed into a properly designed safety circuit include, but are not limited to, safety Interlocking switches, safety interlocking key switches, trapped key systems, electronic tag/fob safety-rated devices, and safety-rated enabling devices.   

Also required: an analysis to clarify the span of control of the exclusive control-safety devices used, to help in detailing the interlocks to the other control systems that are not part of the press-control system.  ANSI B1.20, ANSI Z244.1, and additional B11 Standards such as B11.0, B11.19, and B11.26 all provide guidance, as well as the C level standards for the equipment such as B11.1, B11.2, B11.3 and B11.18 for proper implementation of the performance of the various safety functions. 

Safety-Related Parts of the Control System

Metal formers must understand that the circuit must be more than just the exclusive control device and its application to the press safety-control system.   The device must be part of all safety-control systems responsible for the control of hazardous energy, and each of those systems may include multiple safety functions that the exclusive control device must be part of, as a detecting device within the safety function.

Each safety function contains a minimum of three elements, as shown here. 

press-safety-function-sensors 

 

 

 

 

Note: Each safety function must be analyzed to determine the architecture (category level) for that specific function.  Performance levels and control-reliability analysis also can be used for the analysis.

As previously noted, the OSHA interpretation for recognizing “properly designed safety-control circuits that provide effective protection for control of hazardous energy when using alternative methods for tasks” is based on the accepted methodology of the ANSI term control-reliable safety circuit. Per ANSI B11.26, a control-reliable safety circuit is a minimum of a category 3 circuit architecture--an architecture or design where “no single failure will cause the loss of the safety function.”  

Per ANSI B11.26, the requirements for achieving a category 3 circuit (see the diagram below):

Safety-related parts of the control system of category 3 shall be designed so that a single fault in any of these parts does not lead to the loss of the safety function. Whenever reasonably practicable, the single fault shall be detected at or before the next demand upon the safety function:

  1. when the single fault occurs the safety function is always performed,
  2. some but not all faults will be detected,
  3. accumulation of undetected faults can lead to the loss of the safety function.
  4. Note – item iii above is one of the reasons we perform documented periodic checks at regular intervals, the interval period determined by a risk assessment.ANSIB11-cat-3-circuits

 

In Summary

… the review for applications of alternative methods for the control of hazardous energy in lieu of lockout for press-related equipment serves as a reminder to not overlook the responding element of the above diagram.  That responding element for this type of equipment includes motorized control as well as fluid-power control.  Too often, what looks like a proper safety device utilized for exclusive control is not properly designed within a control circuit that includes the responding unit, that being the element that can cause unexpected hazardous motion.  Only by following all of the requirements within the ANSI documents discussed above can an effective alternative method be implemented, and then proper validation must occur to ensure that all of the requirements, and the risk-assessment analysis, have been met.

Also, while the above information is based on providing a safety-control circuit only for the alternative method control of hazardous energy, realize that at times a combination of both a safety-control circuit and an additional isolation method can be used, especially when dealing with fluid power, until acceptable methods of control circuits can be fully implemented. MF

Industry-Related Terms: Checks, Lines, Transfer
View Glossary of Metalforming Terms

 

See also: White Horse Safety, Inc.

Technologies: Safety

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