Machine Designers Reference. J. Marrs
the hazard.
The machine designer should have a basic understanding of warnings and what factors influence their effectiveness. Effectiveness is influenced by choice of colors, placement, ‘signal words,’ pictogram illustrations, wording of statements, size of letters, and durability, to name a few. The subject of warnings and what makes them effective has been studied and written about extensively. Our discussion presents only very basic information about the subject. For more information, consult industry standards such as ANSI Z535 (series), ISO 3864 (series), ISO 17398, EN 842, EN 457, EN 981 and ISO 7000, along with various books on the subject.
•Be sure to comply with all safety and ergonomics laws, codes, and standards. Consult the recommended resources for more information.
•Physical barrier guarding should be the first choice if a hazard cannot be designed out of the machine.
•Procedural safeguards must be written, and training of personnel should be formalized and recorded.
•Have a qualified safety professional evaluate all equipment, tools, and workspaces.
There are other machine design safety features and issues that cannot necessarily be classified as safeguarding. It is important that all aspects of machine safety be analyzed during the design process and appropriate steps and design features be considered. The following are only some of the safety-related aspects of a machine that were not included earlier in this chapter; designers must be mindful of them during the machine development process.
An excellent source for understanding a machine’s safety goals and the associated design process is industry standard ISO 12100:2010. It is recommended that machine designers not only become familiar with much of the literature cited in Section 2.5, but also become familiar with specifically this standard.
•A list of books and industry standards are provided in Section 2.5 of this chapter.
EMISSION OF AIRBORNE SUBSTANCES OR MODIFICATION OF SURROUNDING ATMOSPHERE
The machine designer must be aware of the potential for the machine to emit undesirable or potentially harmful airborne substances such as mists, vapors, fumes, particles, dust, or other contaminants, or to cause a modification of its surrounding atmosphere, such as enriched oxygen, carbon-dioxide, or nitrogen. Such airborne substance or modified atmosphere, when certain levels are exceeded, could affect not only the performance, safety, or health of individuals, but also potentially the value of surrounding property.
It is important that a machine that emits such substances or gases be designed such that such emissions can be appropriately controlled. Controlling such substance or gases can be accomplished either within the confines of the machine itself (designed into the machine), or through information and instructions provided with the machine, providing information about the emissions (nature of the substance, likely volumes of emission, and potential effects), and instructions or guidelines for their control (the type and basic capacity of emission control equipment needed).
EMISSION OF RADIATION, INTENSE LIGHT, VIBRATION, HEAT
The machine designer must consider the potential for the machine to emit radiation (X-rays, gamma rays, ultraviolet, infrared, microwave, etc.), intense light (welding beam, laser beam, etc.), substantial vibration, or substantial heat. Such emissions, if beyond an acceptable level, can affect the health and safety of individuals in the area as well as surrounding property, and must be controlled. Control can be achieved through the use of radiation filters, screens or shielding, limiting radiation power, providing remote operation, providing vibration isolators or dampers, providing cooling ventilation, etc.
EMISSION OF NOISE
All machines that have moving parts emit noise. According to U.S. OSHA requirements, employers must take steps to control noise employees are exposed to, and achieve, at minimum, levels not exceeding those cited in the regulation (Table G-16 of 29 CFR 1910.95(b)(1); see Table 2-6). Machine noise can be controlled, and designers should understand excessive noise is generally not desirable. Ways of reducing machine noise include increasing the mass of panel material, using sound insulation, damping or cushioning sources of impact or vibration, and reducing or muffling compressed air emissions. When noise at the operator’s ears exceeds limits set in OSHA regulations, hearing protection is required, and such information and instructions must be included with the machine. Machine noise levels should be measured in accordance with ANSI B11.TR5.
Table 2-6: OSHA Noise Exposure Limits
| Duration of Exposure hours | Sound Level DBA (slow response) |
| 8 | 90 |
| 6 | 92 |
| 4 | 90 |
| 3 | 97 |
| 2 | 100 |
| 1.5 | 102 |
| 1 | 105 |
| 0.5 | 110 |
| 0.25 or less | 115 |
| Impulse Noise | 140 peak |
HAND/ARM VIBRATION
Hand/arm vibration (HAV) is defined as the transfer of vibration from a tool to a worker’s hand and arm. The amount of hand/arm vibration is characterized by the acceleration level of the tool when grasped by the worker and in use. The vibration frequencies that most affect hands and arms lie in the 5 to 1,500 Hz range. The types of machines typically associated with significant vibration include chain saws, chipping hammers, grinders, hammer drills, and powered compactors. NIOSH publication No. 89-106 “Criteria for a Recommended Standard: Occupational Exposure to Hand-Arm Vibration,” 1989 (found at www.cdc.gov/niosh/89-106.html) provides helpful information.
WHOLE BODY VIBRATION
Whole body vibration (WBV) is the transfer of relatively low frequency (0.5 to 80 Hz) motion to the whole body through a broad contact area. It is most commonly transmitted through the feet when standing, or through the buttocks when sitting. Off-road unsprung vehicles are the type of machines most typically associated with the vibration, jarring, and jolting associated with WBV. Whole body vibration can jostle organs, contribute to back pain, cause fatigue, and cause a reduction in a person’s work performance. NIOSH, as well as Health and Safety Executive (found at www.hse.gov.uk/), provides additional information on this subject.
MACHINE USE IN EXPLOSIVE ATMOSPHERES
If it is intended or if it is foreseeable that a machine will be used in the presence of an explosive atmosphere (gases, vapors, mists, or combustible dusts), components capable of operating in such atmospheres