What must a warning sign accomplish? First, it must inform a worker, or user or owner of a machine, of the dangers that would not be obvious to him. Second, it must tell him how to avoid the danger. Third, it must be easily understood.
In order to inform him, the sign must be well visible and, in fact, should capture his attention. Thus, the sign should be placed where he may be expected to see it during the normal course of his work. Hence it is better to place a warning sign on a potentially dangerous machine which confronts the user constantly while he is working, rather than place it in an Instruction Book or Owner’s Manual, since the latter is read once, or only occasionally. In the absence of a constant reminder, a worker will tend to lose his sensitivity to the danger as he becomes increasingly familiar with it-providing that no accident has happened yet. Thus, the argument that an experienced worker is safer than an inexperienced one is generally fallacious, since “familiarity breeds contempt” for the danger.
An example of a misplaced warning is a sign on a “cherry picker” – a truck-mounted device used to raise workers to a height-describing the danger of possible contact with high-voltage lines, wherein the sign is placed on the body of the truck rather than on the platform where the workers stand. It is far better to place the sign on the platform, where the workers can see it constantly while in their elevated position.
Where a machine is attended by various dangers, it may not be practicable to warn against all of them by signs posted on the body of the machine. In that case, the warnings must be placed in an Instruction Book or the equivalent, and there should be posted on the machine a warning to the effect that the Instruction Book must be read and understood before the machine is operated-together with one or a few warnings of the chief dangers.
To capture the worker’s attention a warning sign should be large and, preferably, colorful. Further, it should be durable, so as to remain visible and effective over the life of the machine. Embossed (raised] lettering will tend to keep the sign legible in the presence of dirt, and will render the sign more impressive, thereby increasing the probability that its injunctions will be heeded. Such embossed signs are in common use on automobile batteries, warning of the (largely unsuspected) danger of explosion.
Warning signs should be addressed to dangers which on superficial consideration would seem to be obvious, yet which are unforeseen by many laypersons, particularly those lacking good mechanical aptitude. For example, many persons using a clothes-washing machine will not see the danger in starting to remove the clothes before the tub stops spinning, since they do not visualize that their arm may be caught by the whirling clothes and thereby dragged around with the machine. Again, a punch-press operator may take for granted that the ram of the press will descend only when she intentionally activates the appropriate controls, whereas on occasion the ram may descend (or repeat) when not explicitly “ordered” to do so, possibly trapping her hand.
Next we consider the language of a warning sign. To be effective, a warning sign must be easily understood. This means using simple, but strong, words. Although there are many workers who do not read English, nevertheless a sign in English will most likely be read by someone-perhaps a supervisor -who can then communicate the danger to the non-English-reading worker. As for multi-language signs, these tend to become confusing if more than two languages are used. Instead, one can use graphic language, which has an advantage over and above the fact that it requires no reading skill; namely, it often tends to frighten the worker, thereby tending toward better compliance with the warning. For example, instead of KEEP HANDS AWAY FROM KNIFE one can show a picture of fingers being cut. Again, instead of KEEP PROPANE TANK AWAY FROM FLAME one can show a picture of the tank with fire and explosion emanating from it.
Aside from informing the user of the danger, the warning sign should tell him what to do to avoid the danger. Often the nature of the danger is rendered obvious by a description of the means to avoid it, as in the above examples involving the knife and the propane tank. In other cases, a separate description of the danger and of the protective means is called for, as in the following example.
A certain product emits fumes whose inhalation, over a period of time, can lead to illness. One must first explain the danger, especially since the illness develops subtly and somewhat undetectably over a long period. Then one must describe the protective means, which involve adequate ventilation, but not ventilation in the ordinary sense such as is provided by an open window. Rather the air in the workroom must be sucked out constantly by a fan and discharged to the outside, thereby causing new and uncontaminated air to be sucked into the workroom.