Machine Designers Reference. J. Marrs
bars or edges, contact probes, and other devices. These devices protect everyone in the area.
Two-hand controls are primarily devices placed some safe distance away from the danger zone that require both of the operator’s hands to contact cycle start switches simultaneously. The distance from the danger zone is calculated such that operators cannot push the buttons and then quickly move their hands into the danger zone. These devices are also often called “two-hand no-tie-down devices”. These devices protect only the operator, not others who may be in the area.
Gates are physical barriers that move to block access to the danger zone when the machine cycles. These devices protect everyone in the area.
Examples of protective devices can be found in industry standards BSI PD 5304 (including in Section 8), and in other literature cited in Section 2.5 of this chapter. Table 2-5 provides a list of advantages and disadvantages of various point-of-operation protective devices.
Table 2-5: Point-of-Operation Protection: Operator Protective Devices
Based on U.S. Department of Labor, OSHA publication OSHA 3170-02R 2007
PROCEDURAL SAFEGUARDING: INFORMATION, INSTRUCTIONS AND WARNINGS
Information and instructions, customarily in the form of machine manuals7, are an integral part of a machine. Manuals provide information and instructions about the machine and its use. Information and instructions should be complete enough to ensure proper and safe installation, set-up, use, and maintenance. Instructions are important, but on their own, they are not enough to ensure operators will work safely.
Regarding specifically safety, manuals must also include information and warnings about hazards and risks that may not be known to users, not just when the machine is used as intended, but in reasonably foreseeable misuse situations as well. Although there is not a duty to warn of hazards that are open and obvious (the sharpness of a kitchen knife, for instance), it is important to understand that what may be obvious to a machine’s designer may not be obvious to an ordinary user. Procedural safeguarding, the 3rd, 4th and 5th priorities8 in the machine hazard risk reduction hierarchy list, starts with the information, instructions and warnings found in the manual. This section is intended to be only a brief introduction to the subject. The reader is encouraged to become familiar with books and industry standards on the subject, some of which are cited in Section 2.5.
Regarding warnings, when a hazard that can cause serious injury cannot be designed out of a machine (or protected by its remote location) and cannot be effectively safeguarded by a barrier guard or protective device, if the hazard is not obvious or readily known to an ordinary user, there is an obligation to provide a warning likely to be seen and understood. Although warnings provide information and instructions about hidden or unknown hazards, it must be understood that they have a limited impact on making mishaps less probable. The ultimate aim of a warning is to alter behavior, by encouraging an individual either to do something, or to avoid doing something.
Once it is determined that a warning is needed, the resulting warning must be crafted to be, at minimum, “adequate.” An “adequate” warning is one that would lead an ordinarily reasonable person to understand the hazard and take steps to avoid harm. In general, a warning can be viewed as “adequate” if:
-the warning is in a form that could reasonably be expected to catch the attention of a reasonably prudent person,
-with a message understandable to the ordinary user,
-conveying a fair indication of the nature and gravity of the harm that could result from the hazard,
-conveyed with a degree of intensity that would cause a reasonable person to exercise appropriate caution.
The development of a warning can be a simple process of providing understandable information and instructions in an effective way or, in some situations, a complex process involving product research, message development, and focus group responses. In all cases, warnings—both those included in manuals and those posted on machines—for them to be “adequate” must be clear, readable, and understandable to the ordinary user.
WARNINGS INCLUDED IN THE MANUAL
Warnings included in a machine’s manual must be capable of conveying the same information as those posted on the machine itself. When writing warnings for the manual, the following should be considered:
•All warnings a user may need to know about should be included in the manual.
•From a style perspective, warnings in a manual must be reasonably consistent with each other, and they must be consistent with the warning labels posted on the machine.
•Warnings that warrant the “DANGER” level (DANGER being the most serious level) must be not only included in the manual but also posted on the machine itself.
•Warnings must stand out from the rest of the information in the manual.
•Never mix warnings with ordinary instructions.
•Never bury warnings in the text in such a way that it might be missed.
•If there is a section in the manual dedicated to listing all warnings and safety instructions (at the beginning of the manual, for instance), also include the warnings elsewhere in the manual text where appropriate.
•It is good practice to illustrate in the manual every warning label posted on the machine, indicating its location on the machine. Along with these illustrations, it is good practice to provide the label’s part number to simplify replacement if necessary.
It must be remembered that not all individuals who will be operating the machine will have had access to or have read the manual. And many who have read the manual will not remember certain pieces of information contained within. It is important to remember that for a warning to be effective, it must be seen, read, understood, remembered, and heeded. As a result, warnings placed only in the manual will not likely meet at least one of the requirements for it to be deemed “adequate.”
WARNING LABELS POSTED ON THE MACHINE
Warnings located in the manual are simply not going to catch the attention of a machine user who has not read it or doesn’t recall its contents.
Some hazards that cannot be eliminated or guarded are serious enough to warrant the posting of warning labels on the machine itself. The design of machine-posted warnings has developed over the years, based on industry experience and controlled studies. One definition of an effective warning is one that changes behavior in a way that results in a net reduction in negative consequences. It has been found that the effectiveness of machine-posted warnings improves when warnings:
•are located near the zone of danger itself,
•are conspicuous (eye-catching) and in a location likely to be seen,
•have a ‘signal word’ of appropriate strength (such as “CAUTION” or “WARNING” or “DANGER”), indicating the seriousness of hazard,
•have a hazard statement informing the reader in a clearly stated manner what the danger is,
•have a consequence statement telling in a clearly understandable way of the consequence of the hazard,
•have an instruction statement providing clearly stated instructions