Machine Designers Reference. J. Marrs
be selected. The industry standards EN 1127-1, EN 50020, EN60204, as well as UL standards titled “Hazardous (Classified) Location ...” and the European Union directive ATEX95 94/9/EC provide guidance in such situations.
MOVING THE MACHINE
When it is determined moving a machine is hazardous, then provisions for jacking, lifting, and hoisting should be provided to help the moving process and enhance safety. When it is foreseeable that a machine’s weight, center-of-gravity, or lift point material strength could be misunderstood by movers, moving instructions should be made available and made obvious to movers. These instructions should provide such information as the machine’s weight, center-of-gravity location, lift points, loose component tie-down points, and other information necessary for a safe move. Professional riggers should be used to move extremely heavy, large, awkward, or sensitive machinery.
MACHINE STABILITY
A machine must be sufficiently stable for it to be used as intended safely. Its weight distribution and base footprint must be such that it remains stable, taking into account machine vibration, dynamic movement of components, movement of work pieces, foreseeable mishandling, accidental bumping, forces of nature, etc. If necessary, provisions should be provided for anchoring (bolting) the machine into position (to the floor, for instance).
LUBRICATION
To avoid exposing individuals to unacceptable risks when lubricating a machine, lubrication points should be located in accessible and safe-to-reach locations, when possible.
DANGER WARNING ALARM SIGNALING: AUDIBLE SIGNALS AND VISUAL SIGNALS
When the health or safety of an individual is put at risk by an unstaffed machine in a defective or dangerous state, according to accepted industry standards the machine must be equipped to transmit an appropriate audible or visual warning alarm signal indicating the danger. The warning alarm signal must be immediately and easily recognized and understood; it must have priority over all other signals (except not over emergency signals, which have absolute priority). The characteristics of warning signals are outlined in industry standards, including EN 981, EN 842 and EN 457.
Audible danger signals must be such that anybody who hears them recognizes them and can react immediately. The characteristics which make a danger signal effective are its sound (audibility), its ability to be recognized immediately (discriminability), and that there is absolutely no doubt as to what it refers to (unequivocability). For further details, industry standard EN 457 is recommended as a reference.
Visual danger signals must be designed such that that anybody who sees them will recognize them and respond immediately. A visual danger signal must be clearly visible, even in strong light (visibility), distinguishable from other lights and light signals (distinguishability), and understood immediately (unequivocability). The visual signals must be positioned where it reaches all of the area affected, and its message must be clearly understood — whether it refers to a machine, a group of machines, a production line, or a complete department. For further details, industry standard EN 842 is recommended as a reference.
LOCKOUT/TAGOUT REQUIREMENTS
Federal OSHA regulations (29CFR1910.147) require employers to ensure that all new machines provided to employees are capable of being locked out during service and maintenance for the purpose of preventing unexpected start-ups, the energizing of machinery, or the release of stored energy that could cause injury to employees. The lockout standard applies if (1) the employee is required to remove or bypass a guard or other safety device during service, (2) an associated danger zone exists during a machine operating cycle, or (3) the employee is required to place any body part into the machine’s point-of-operation area.9
All new machinery and equipment needs to be designed to accept lockout devices.10
EMERGENCY STOP DEVICES
An emergency stop device is a manually actuated control device that requires deliberate action to bring the machine to a stop when a dangerous situation is recognized. The E-stop (emergency stop) device must be continuously operable and within easy reach. Each operator panel must contain at least one E-stop device. Additional E-stop devices must be available and readily accessible, at minimum, wherever a machine operator is intended to be or would foreseeably be during normal operation. E-stop devices should stop the machine as quickly as possible without generating additional hazards. Emergency stops must safely neutralize energy to and within that portion of the machine affected, including electrical power as well as pressurized air. E-stops are not safeguards, and are not alternatives to safeguarding.
Because emergency stop switches and circuits can remain inactive for long periods of time, it is important that they be designed with reliability in mind. In addition, instructions for maintenance requirements and periodic testing are important to assure confidence that the system will function as intended.11
Emergency stop components and circuitry must be failsafe, and the appropriate components for E-stop use are normally clearly identified by component manufacturers. Emergency stop devices come in various forms, the most common of which are cable pulls and mushroom-type button switches. When an E-stop device is actuated, it must latch in, and it must not be possible to generate the stop command without latching in. The resetting of an E-stop device must not cause a hazardous situation. To restart the machine, a separate and deliberate action must be required.
Emergency stop device details can be found in industry standards BSI PD 5304 (section 5), EN 418, EN-13850, ISO 13852 and ISO 13850. Design and selection of components for E-stops should be performed by a qualified controls professional.
•Comply with all laws, codes, and standards governing environmental hazards. Consult the recommended resources for more information.
•Design of an E-stop circuit and selection of related components should be conducted by a qualified controls professional.
•Lockout/Tagout procedures are required by law to isolate all sources of energy (electrical, pneumatic, hydraulic, mechanical, etc.) when maintenance activities are performed. Consult the recommended resources for Lockout/Tagout procedures and requirements.
•Have a qualified safety professional evaluate all equipment, tools, and workspaces for environmental and machine hazards.
Machinery safety and ergonomics information is found in governmental statutes, codes and regulations, industry standards, handbooks, textbooks and manuals, and scientific and technical literature found in magazines, journals and periodical articles. Safety requirements are found in governmental statutes. Safety expectations — just as important for machine safety — are found in various books, standards and periodical literature.
Society’s expectations of what is acceptable relative to product safety evolves with time, and usually it is the industry standards, and the books, that most accurately reflect what society views as the ‘best practices’ to achieve what is viewed as reasonably safe. For this reason, although governmental statues are certainly important and necessary to be included in this literature list, the designer should understand that well-organized books and up-to-date industry standards are of paramount importance in designing safe machines and products. Because of the fluidity and time-limited exposure of periodical literature, this chapter does not attempt to cite notable magazine articles, journal papers, technical studies, government ‘fact sheets’ and bulletins, or other such literature, despite their importance.
GOVERNMENTAL REGULATIONS, STATUTES, CODES AND PUBLICATIONS
•Code