Machine Designers Reference. J. Marrs
machine hazards at the earliest stages of design. It is a means of creating an initial list of all hazards that may exist in every machine area and system and operation. It helps overcome the tendency to focus only on immediately obvious hazards, forcing an evaluation of potentially more serious or hidden dangers within a machine. Proposals for safety measures are the end result.
The DELPHI Technique involves providing questionnaires to a group of experts, individually, in successive steps. The results of the previous round of questions and answers, together with additional information from the others in the group, are communicated back to the participants. During the third or fourth round, the questions concentrate on those issues for which there is little or no general agreement. Because of its use of experts, this technique is notably efficient.
It should be understood that there are many methods of hazard identification and analysis. These listed are only a few. Each method has advantages for certain applications; therefore, it may be necessary to adjust or combine methods to match the situation at hand. It is important, whatever method is or methods are chosen, that hazard identification and analyses be performed early and often during the design process.
RISK REDUCTION
Risk Reduction is the process of taking sequential steps to either eliminate hazards or reduce hazards to an acceptable level. Although there are variations of lists of such steps, the following steps are commonly cited (listed in sequential order of most effective to least effective):
1.Eliminate or reduce the severity of the hazard (design the hazard out).
2.Safeguard the hazard (barrier guards or protective devices).
3.Instruct and warn the user (in manuals, and when appropriate, on the machine).
4.Describe requirements for training the user (safe work procedures training).
5.Recommend personal protective equipment (ear protection, eye protection, etc.).
The Risk Reduction process, unlike the Risk Assessment process, requires actual design creations and decisions — some take the form of designs that eliminate or provide safeguarding for hazards; others are in the form of warnings, instructions, or information (literature and manuals that provide information, instructions, and warnings are a part of the total machine). When risks have been properly assessed, and when the machine’s design has satisfactorily reduced the risks, the resulting machine can be judged to have reached its safety goals. The Risk Assessment / Risk Reduction iterative cycle would then be complete. (For a detailed understanding of this process, refer to industry standards ISO 12100:2010, ANSI B11-2008, and others listed in Section 2.5.)
•Be sure to comply with all safety and ergonomics laws, codes, and standards. Consult the recommended resources (Section 2.5) for more information.
•Conduct Risk Assessments on all designs and processes. Conduct risk analysis early and often during the design process.
•Designing a hazard out should be the goal of any risk reduction activity. If this is not possible, other methods may be employed.
•Risk of long-term repetitive use injury should never be underestimated. This is an important factor in the design of workstations, tools, and industrial equipment.
Most machines have moving parts, both rotating and linear-moving, that can cause injury. Moving machine parts may be found in numerous locations on or around a machine, including:
(a)At the point of operation where work is performed on the work piece or material,
(b)In the power transmission components that transmit power throughout the machine (shafts, pulleys, belts, sprockets, chains, flywheels, couplings, spindles, gears, cams, cranks, rods, and other moving parts), or
(c)In other moving parts of the machine (machine components that move during operation, such as rotating parts, reciprocating parts, or traverse-moving parts).
All parts that move have the potential to contribute to accidents that can result in personal injury. Both rotating motion and linear movement can be dangerous.
Rotating components, even smooth rotating shafts, can grip an item of clothing or hair — even skin — and draw it into the machine. The danger of rotating components increases if they contain irregular or uneven surfaces or projecting parts, such as adjusting screws, bolts, slits, notches, or sharp edges. Rotating machine parts can also create dangerous in-running nip points with adjacent rotating or wedging components.
Vertical, horizontal, and reciprocating motion can cause injury in several ways, including causing a person to become caught between a moving machine part and some other object, shoving or knocking into a person, catching a person in a nip point, or causing injury with an unexpected movement of a sharp edge.
In addition, many machines have hydraulic or pneumatic systems that transmit power, or components that store energy. Springs, components under pressure, and elevated masses are examples of stored energy that can be released suddenly and hazardously. These power-transmitting and energy-storing components, should they fail or be released unexpectedly, pose hazards that must be considered during the machine design process. For example, a burst hydraulic line can spray oil that can be scalding hot, or can produce pin-point spray capable of penetrating skin. A whipping hose can become violent. A failed pneumatic fitting can release a potentially dangerous blast of compressed air, or release the pressure on an air cylinder causing unexpected movement and potentially dropping a load. The sudden release of a deflected spring or sudden drop of an elevated component can be very dangerous.
If a given hazard cannot be designed out of a machine (or neutralized by the nature of its remote location), then safeguarding, in some form, must be provided. Safeguarding can be categorized as either Designed-into-the-machine safeguarding, or Procedural safeguarding. (Procedural safeguarding is sometimes known as Information for use, or information and warnings).
Designed-into-the-machine Safeguarding can be either a guard, which is a physical barrier that prevents access to a hazardous area, or a protective device, which is a safeguarding means other than a barrier guard that controls access to a hazardous area. Examples of protective devices are photoelectric curtains, cable pull-backs, pressure sensitive mats, trip bars, and two-hand controls. Protective devices are often used to control access specifically to a machine’s point of operation. Guards and protective devices can be (and often are) integrated together (an interlocking guard, for instance) when appropriate to enhance productivity or further enhance overall safety. Safeguarding will be detailed later in this section.
Procedural Safeguarding (Information for use) is information, instructions, procedures, and/or warnings posted on the machine, in manuals, or in training sessions instructing individuals how to operate the machine, how to avoid certain actions, or how to take certain steps to avoid a particular hazard. Procedural safeguarding is inherently less effective than barrier guards or protective devices designed into the machine because it relies on factors that are unpredictable. Procedural safeguarding relies on every individual doing everything in accordance with all instructions — 100% of the time — with no exceptions.
Safeguarding that is designed into a machine is far more effective than procedural safeguarding (information and warnings). Only when the hazard cannot be designed out of the machine and cannot be effectively safeguarded (the 1st and 2nd steps in the sequential Risk Reduction steps — see earlier) should the designer turn to those steps that fall into the ‘Procedural Safeguarding’