The revised LO/TO standard addresses the use of key-controlled locks and identifying tags that are used to shut down and lockout sources of hazardous energy that could otherwise result in personal injury if energy were unintentionally released during maintenance or service. The foundation of the LO/TO standard is its use of a systematic procedure designed to identify, analyze and correct safety problems.
Combined with personnel training and follow-up audits, using LO/TO procedures enables personnel to develop a better grasp of safety and improves plant operations. Improving plant safety will bring financial gains through improved machine availability and throughput, as well as lowered health and liability insurance rates.
Complying with ANSI Z244.1 requires an accurate and complete tabulation and risk assessment of every piece of equipment and machinery, including out-of-service and surplus equipment. Such assessments typically result from working with supervisors and operators at all levels in the plant and on the plant floor. Early participation by everyone will help reinforce commitment to the safety program.
The program requires a safety administrator, a knowledgeable individual, who is responsible for all aspects of the safety program and has the authority to act on the assessment findings.
Before initiating a hazardous energy control methodology and risk assessment, the safety administrator needs to understand the following basics:
1. Definitions of machinery and energy hazards;
2. The scope and application of the LO/TO standard;
3. Qualified exceptions to the rule; and
4. Any unusual circumstances that result in accidents.
Start by considering all energy sources. Under the standard, this includes electrical, mechanical, hydraulic, pneumatic, chemical, nuclear, thermal and gravity. Don't forget to consider stored energy, such as large capacitors, hydraulic and pneumatic accumulators and batteries. Each has its own set of hazards and each may require different methods of isolation or energy reduction. Assess every energy source in detailed written procedures. Remember, in some cases, a machine or piece of equipment may be powered by more than one power source, or have hidden or latent sources of energy. A common example of two power sources would be a machine tool with electrical and compressed air supplies.
LO/TO does not cover normal machinery operation. However, additional safety equipment and operational considerations may be required. LO/TO applies when anyone performs a hazardous duty, including servicing or maintaining equipment, removing or bypassing a guard or other safety device, or placing part of their body on a machine or in a "danger" zone when performing maintenance, tooling changes or set up.
Step by Step
Taking an equipment inventory and developing a comprehensive hazard assessment seems to be an onerous job. Working with the appropriate supervisors, operators and anyone else familiar with operations and using a "machine-by-machine" approach makes the job manageable. The inventory needs to include every piece of out-of-service and surplus equipment.
Determining the risk associated with each machine and piece of equipment can be broken down into seven steps. First, identify all tasks (including foreseeable misuse) and related hazards. Does a machine have more than one motor or valve which could release hazardous energy? Is there more than one energy source?
After documenting all energy sources, someone familiar with safety hazards performs the second step identifying each potential safety hazard associated with each machine.
A hazard assessment must also consider all possible situations that could result in injury, from start-up of a machine to accidental release of stored energy. Once completed, the assessment becomes the foundation for developing complete and thorough energy control procedures.
At a minimum, the hazard assessment should be based on rating each hazard for the potential frequency of exposure and the potential severity of injury. Don't forget to include possible human error, deficiencies in the management system (written procedures), as well as foreseeable misuse of the machine. This stage demands a consistent and reasonable rating system.
Potential frequency of exposure refers to how often someone must enter a hazard area, and the amount of time spent there. Also consider the number of people that may come in contact with a potential hazard.
Probability of occurrence may also be considered when determining the risk level. Probability takes into account the operating factors of the machine. What safety guards and systems are in use or need to be used? How fast does it cycle? A history of the machine's reliability and failure modes, combined with the accident history by task or activity at the machine, provides insight into the probability of an accident.
The safety administrator should also consider how users interact with the machine (both operators and maintenance). How competent are the people working on the machine? Can the safeguards be defeated? Consider the working environments. Does a noisy or dusty environment make a task more difficult?
The information collected during the first steps of the assessment must then be evaluated for each identified hazard. A subjective process, the safety administrator must compare risks in similar situations, determine a consensus appraisal of the risk hazard, and finally, make an informed value judgment.
Looking at each task, the safety administrator identifies each hazard associated with it, the level of exposure (Frequent, Periodic, Infrequent) and the severity of the injury (Catastrophic to Minor) to determine the level of risk. If a hazard is determined to have an acceptable level of risk, the process does not need to go further until a review is required.
For applications with an unacceptable risk level, the process of reducing risk continues by identifying potential control actions from a hierarchy of elements that may produce an acceptable solution, such as eliminating a hazard through machine design. Other possible solutions include:
1. Using special oil or grease fittings that extend beyond a safety guard to eliminate the need to enter a hazard area;
2. Using an engineered safeguard, a cage or gate (fixed or interlocked), a safety light curtain or safety mat;
3. Including warning and alerting techniques (sirens, beepers and lights);
4. Implementing administrative control such as documented work procedures enforced with training and audits;
5. Using personal protective equipment with appropriate training.
From the list of potential methods, the safety administrator needs to identify the selected control actions chosen as the best protective measure(s). After the selection has been made and implemented, the system effectiveness needs to be verified. In general, a safety administrator can ask questions to determine if a risk hazard is sufficiently reduced.
1. Can the task be performed and not cause injury or health problems?
2. Have all appropriate safety measures been taken for every task or activity, and are all safety measures compatible with each other?
3. Do the safety measures themselves cause any new or unexpected hazards or safety problems?
A review of the safety program will determine if the result produces an acceptable level of risk. If not, or if hazards have been missed, the process must be repeated until the residual risk is acceptable. Finally, when the process is complete and results in an acceptable level of risk, the entire risk assessment process should be documented.
Alternative and Industry-Specific Methods
As comprehensive as LO/TO may be, the standard also allows for both alternative methods and industry-specific examples to ensure worker safety. Industry-specific methods are included in the annexes of the standard, including alternative methods for the printing business (Appendix H) and plastics industry (Appendix I) and their industry-specific standards are referenced.
Depending on circumstances and the type of equipment used, ANSI Z244.1 lists five alternative methods: engineered safeguards, warning and alerting techniques, administrative controls, training and personal protective equipment. Alternative methods address other options to help ensure worker safety. The following describes alternate uses of machinery safety equipment as a method to control hazardous energy.
Freeze Plug Applications Annex F of the standard describes a technique for freezing liquids in a pipe and controlling hazardous energy. This technique provides a non-intrusive method for the isolation of piping systems, provided that the material has a suitable freezing point. A cryogenic supply system is used to freeze the section of piping. Tags and locks are used to prevent the cryogenic supply from premature shutdown.
Remote low-voltage lockout system These devices isolate hazardous energy located directly on a machine and are covered in Annex G of the standard. By permitting convenient location of the lockout device in a user-friendly manner, devices can be located at multiple process points to encourage lockout protection.
This is a dedicated safety system with dual-channel, low-voltage safety switches. It uses redundant circuits and monitoring by safety interface modules to provide control reliable operation. The system cannot be reactivated until the repair is made. These devices must be installed and maintained according to manufacturers' guidelines by qualified personnel.
Robotics As discussed in Annex J, these applications combine a dynamic workspace with specific process hazards. Personnel performing routine activities (i.e. teaching, servicing, minor tool changes, removing jams and troubleshooting) expose themselves to hazardous energy. Provisions of alternative control of hazardous energy in robotic applications are contained in ANSI/RIA R15.06-1999 Industrial Robot and Robot Systems Safety Requirements.
Based on the premise that the personnel performing the task have total control of the robot or system and the peripheral equipment and process hazards, alternative methods for a typical task may include any of the following:
1. Disable the automatic task program;
2. Isolate the hazardous energy to the motors;
3. Use of an enabling device by each person entering the safeguarding space;
4. The emergency stop circuit always remains functional; or
5. Certain tasks can be performed by placing the robot arm in a predetermined position, or utilizing devices such as blocks or pins to prevent hazardous motion of the robot or robot system.
Trapped-key interlock Safety switches using a trapped or captive key system ensure that a predetermined sequence of events takes place. For example, consider three unique keys released when turning electrical power switch A, opening mechanical switch B and closing pneumatic valve lock C. These keys A, B and C are then inserted in a trapped-key exchange unit which releases key D, which is used to unlock the machine access door.
The same trapped-key system can also ensure that a specific sequence of operations occurs when working with dual relief valve piping. Using a sequence of marked keys, employees can work on one relief valve system while ensuring the other is still open. It also guarantees that the employees do not inadvertently shutdown both relief valves.
Trapped-key systems are available in a wide variety of configurations and capabilities, including electrical rotary switches, solenoid key releases, time delay units, bolt interlocks, valve interlocks and various key exchange units. These systems offer unique safeguarding solutions for complex machine and process lockout needs. Annex K provides examples of trapped key applications.
With an emphasis on practical applications of lockout/tagout, the acceptance of both industry specific methods and standards, ANSI/ASSE Z244.1-2003 appears to be one of the more detailed and pragmatic safety standards. It certainly provides an opportunity to improve plant safety programs, comply with safety regulations and help a company's the bottom line.
Be safe out there!
Sidebar: Exceptions to LO/TO Rules
A safety standard attempts to address a broad range of applications. As wide ranging as LO/TO is, there are situations that are exceptions to the rule.
First, minor tool changes and adjustments (i.e., centering a conveyor belt) do not apply if they are considered "routine, repetitive and integral" to the operation of equipment during production. Note that this is acceptable only as long as the operation performed uses "alternative measures of effective protection." Documenting procedures and training that specify an alternative method increases their effectiveness.
Examples include using a tool to remove a jam, rather than a hand in a hazardous point. Another is using a local disconnect switch that is under the complete control of the operator.
Another exception includes servicing plug-connected electrical devices, as long as they are unplugged and the plug stays under the exclusive control of the worker performing the maintenance.
In rarer cases, LO/TO excludes "hot tap" operations such as transmission and distribution lines for gas, steam, water or petroleum products when performed under pressure, when continuity of service is essential, and when employees have alternative protection that is equally effective.
Joseph J. Lazzara has been the president and CEO of Scientific Technologies Inc. (STI), a provider of machine safeguarding products in the United States, since 1993 and has been employed by STI since 1981. Prior to 1981, he was employed by Hewlett-Packard Co. in environmental, health, safety and process engineering management. Lazzara received a B.S. in Engineering from Purdue University and a MBA from Santa Clara University. He is past member of the Board of Directors of the American Electronics Association, the Board Executive Committee of the AEA and past chairman of the AEA's Competitive Excellence Committee. Lazzara also served as past chairman of the EHS Committee for the Association of Manufacturing Technology.