Machine Designers Reference. J. Marrs
1-17: Neuber’s Constant for Notch Sensitivity
Table 1-18: Linear Motion with Constant Acceleration
Units: always check all units for consistency
Table 1-19: Rotary Motion with Constant Acceleration
Units: angles in radians
Table 1-20: Work and Power
Units: distance in feet, force in pounds (lbf,) power in foot pounds per second
Co-Written with E. Smith Reed, P.E.
Contents
2.2MACHINE SAFETY: DESIGN PROCESS
Tables
2-4Point-of-Operation Protection: Barrier Guards
2-5Point-of-Operation Protection: Operator Protective Devices
2-7Selected Codes and Standards for Machinery Safety
Figures
2-1Body Dimension Illustrations
2-3Reaching — Grasping — Moving Illustrations
2-4Guard Openings vs. Distances from Point of Danger
Today, successful machines or products must not only perform their intended functions, and perform to customers’ expectations, but they must do so without creating unnecessary hazards that could cause personal injury or property damage. Although no machine is perfectly safe (nothing is perfectly safe), machines are expected to be reasonably safe. They are expected to meet not only safety standards required by governmental codes and regulations, but also standards and criteria found in voluntary industry standards, as well as applicable international standards. In addition, they are expected to consider information and guidance found in textbooks, handbooks, and design manuals, and guidance found in various industry publications (technical journals, published seminar papers, magazine articles, etc.). Even industry customs and practices should be considered when addressing machine safety.
Machines (products in general) need to be designed to minimize, within reason, the possibility of personal injury or property damage. Machine designers must anticipate situations and events that are reasonably foreseeable relative to individuals operating the machine, individuals working on or around the machine, and individuals simply in the vicinity of the machine. They must consider the various ways the machine could cause or become involved in a mishap and the various ways a person could get hurt. Designers must consider the possibility / likelihood of a person getting caught, nipped, pinched, drawn-in, trapped, entangled, crushed, struck, run over, cut, sheared, abraded, punctured, injected, jolted, vibrated, dragged, flung, wrenched, radiated, burned, scalded, blinded, deafened, poisoned, sickened, asphyxiated, shocked, electrocuted, overexerted and overextended, as well as losing a grasp, losing footing, losing balance, slipping, tripping, misstepping, falling on, falling into and falling off. In addition, machine designers must consider the machine’s potential to cause harm to animals (unintentionally becoming caught, injured or killed), property (being struck, contaminated, chemically altered, weakened, flooded, overloaded or burned), or the environment (unacceptably polluting or unacceptably altering environmental or biological systems). The best and most effective time to assure a machine is reasonably safe is during the design process, not after.
Ergonomics is closely tied with machine safety. Ergonomics, sometimes referred to as ‘human factors,’ is a technical discipline concerned with (relative to design of machinery) interrelationships between humans and equipment. Ergonomics is applied for the purpose of integrating human capabilities and limitations with equipment characteristics, not only to reduce operational and safety issues and problems, but also to improve human-work effectiveness. The types of problems that can be mitigated by the application of human factors include: the failure to perform a required task, performing a task that should not have been performed, the failure to recognize a hazardous condition, a wrong decision in response to a problem, inadequate or inappropriate response to a contingency, or poor timing to a response, to name a few. For a machine to be reasonably safe for its operators or bystanders, ergonomics (human factors) must be part of the design process.
The subjects of machine safety and ergonomics have been written about in a number of well-researched books. In addition, industry safety standards have been created through collaborations of experts in their fields. It should be noted that the books and standards cited at the end of this chapter are not the only literature to which one should refer. They represent, however, a useful cross-section to which a machine designer can refer to understand today’s expectations. The reader must understand that the material in this chapter is necessarily brief and general in nature. Hopefully, this introduction will encourage every designer to read further and seek a better understanding of the subjects. Section 2.5 of this chapter provides a list of recommended resources.
Ergonomics is a discipline that studies humans, their characteristics, capabilities, and limitations, in relationship with their surroundings.