Assessing cutting and forming machine tool safety
The expanded breadth of recent standards typically includes the entire life expectancy of machines, the full scope of possible risks, the frequency and severity of risks, and the possibility of harm.
During the past decade increasingly comprehensive machine tool safety standards have been adopted in many countries, including the U.S. The expanded breadth of recent standards typically includes the entire life expectancy of machines, the full scope of possible risks, the frequency and severity of risks, and the possibility of harm.
In the U.S. a new American National Standards Institute (ANSI) technical report published by The Association for Manufacturing Technology (AMT), McLean, Va., in November 2000 addresses these issues and will impact all manufacturers and users of cutting and forming machine tools significantly.
The report is entitled "Risk Assessment and Risk Reduction—A Guide to Estimate, Evaluate and Reduce Risks Associated With Machine Tools." It also is known as TR-3 and provides guidelines for manufacturers, modifiers, and users to perform the hazard analysis and risk reduction assessments called for in many of the B-11 family of machinery safety standards.
For the first time under ANSI in the U.S. machine tool realm, the TR-3 guidelines describe a process that can be followed to reduce risks to acceptable levels and provide suggestions for documenting the work and results.
ANSI has coordinated the development of more than 11,000 product safety standards nationally. Cutting and forming machines are grouped in ANSI subcategory B-11, which includes 21 standards for machine tools and manufacturing cells. AMT is the accredited secretariat for B-11 and ensures that all B-11 standards conform to ANSI's guidelines and procedures.
The Accredited Standards Committee, ANSI's sanctioning group of approximately 30 trade associations, insurers, several international unions, and a few large vehicle manufacturers that are directly impacted by machine tool safety standards, has approved the report.ANSI Standard Composition
ANSI standards are industry-consensus standards written by committees of representatives from manufacturers, users, labor representatives, and others knowledgeable in the industry. The 23 B-11 standards are intended to minimize the risk of harm to all personnel coming in contact with machine tools throughout the lives of the machines.
The standards describe manufacturers', modifiers', and users' responsibilities in performing hazard analysis and risk reduction reviews of their machines. While compliance with these standards is voluntary, the Occupational Safety and Health Administration, which, with a few exceptions, does not have its own machinery safety standards, refers to these ANSI standards in its compliance assistance and enforcement.
Several B-11 technical reports have been written to assist in implementing the 21 standards. TR-3, the latest report, provides a comprehensive, iterative methodology for analyzing and increasing machine safety.
It provides a comprehensive scope of possible sources of harm to individuals, so safety auditors are guided to consider almost all possible sources of harm when performing safety assessments. It also provides a methodology for performing a safety audit and criteria to help the safety auditors to conclude when a machine can be deemed acceptably safe.
A team of almost 50 safety professionals from industry, labor, the military, and OSHA took more than three years to write TR-3. Some of the subject material was new, and spirited discussions ensued as to what information should be included and how it should be presented most clearly and effectively.
Perhaps the most enlightened statement in TR-3 is the acknowledgement contained in the introduction that " ... zero risk does not exist and cannot be obtained." It goes on to state in clause 8.5 that " ... The risk reduction process is complete when ... tolerable risk has been achieved for ... the machine as a whole." All B-11 machine tool safety standards identify risks and often state specific operating procedures to prevent harm to personnel, but none addresses the issue of tolerable levels of risk.
TR-3 lists seven factors to be assessed when determining the achievement of tolerable risk:
- Risk reduction benefit
- Economic impact
- Technological feasibility
- Ergonomic impact
- Durability and maintainability
The report encourages those performing safety analyses to consider the tasks people perform when interacting with a machine or machinery system throughout its life. Tasks are performed not only by operators, but by maintenance, setup, cleaning, inspection, and other personnel.
Often the work performed by those other than the operators, especially setup and maintenance, is carried out under higher risk conditions than those faced by the operators. Occasionally maintenance personnel must diagnose machine problems with the power on and safety equipment disabled or removed.
While exposure time may be low, the risk may be much greater, and the seriousness of an injury also may be higher. Thus, a task-based analysis, which recognizes all the foreseeable work that will be done on a machine, including nonstandard and occasional tasks, results in a more comprehensive audit and leads to reducing the frequency and magnitude of personal injuries.
The risk analysis process begins by determining the capacity of the machine and the location and conditions in which it will operate. This is followed by identifying all tasks that will be performed on the machine, including operation, setup, maintenance, relocation, repair, and other occasional or infrequent activities.
The list of tasks includes those performed during normal or expected use of the machine and those that may result from reasonably foreseeable misuse of the machine, such as overloading or overspeeding.
Once the tasks are listed, the prospective hazards associated with each of these tasks need to be identified. Annex A to TR-3 contains an extensive list of hazards and hazardous situations to assist in the analysis. Each task-hazard pair then needs to be analyzed to determine the risk level posed to vulnerable users.
Risk comprises two components: the probability that harm could occur and the anticipated severity of that harm. This assessment may be affected by how quickly the threatened party becomes aware of the hazard and, once aware, the ability to mitigate it. The report suggests a hierarchy of harm levels, and several categories of probability assist the safety auditor in the analysis.
The risk levels of the task-hazard pairs are influenced by workplace and human factors. Workplace influences include plant cleanliness, lighting, and ventilation. Human factors include training, motivation, health, and attitude. Risk levels also are affected by the reliability of safety controls and equipment and the ability to circumvent them.
After the potential hazards are identified and the level of risk is determined for each task-hazard pair, the level of risk can be estimated. TR-3 provides a methodology for this process and contains extensive guidelines and commentary for the widely recognized hierarchy of risk reduction, namely:
- Design improvements.
- Personal protective equipment.
Risk reduction is an iterative process because each change made to improve personnel safety affects other aspects of the machine, which, in turn, must be analyzed with the revised conditions. Further, it must be a mutual process by manufacturer and user because each party has significant influence over the safety of the personnel working with the machine.
Safety Standard Firsts
ANSI B-11 Technical Report 3 is the first document in the B-11 family of 23 machine tool safety standards to acknowledge that some level of risk always is present to personnel who are involved with machine tools. It also is the first document to provide comprehensive guidelines for assessing hazards and risks and offer practical techniques for reducing risks to acceptable levels.
As such, this report should become a useful reference document for safety practitioners throughout the machine tool industry.
The FABRICATOR is North America's leading magazine for the metal forming and fabricating industry. The magazine delivers the news, technical articles, and case histories that enable fabricators to do their jobs more efficiently. The FABRICATOR has served the industry since 1971.