Why? Why is it that one of the biggest aggravations in product safety is that of markings? For some reason, it seems that we can never get the markings right the first time. Furthermore, it seems that markings that have been acceptable for years will suddenly go bad.
Recently, a certification house criticized a product because of the use of “T” in the designation for a North American fuse. The use of the “T” supposedly is reserved by IEC 127 for indicating time-lag or slow-blowing characteristics of IEC 127 fuses. The certification house would not allow the use of the “T” in the designation of a North American fuse.
In a second incident, a certification house criticized a product because of a missing isolation symbol. On the one band, we have provided too much information, while on the other hand, we have provided insufficient information.
In both cases, the product is deemed not to comply with the standard and is treated to the same extent as if the product was hazardous. The implication is that the marking, or lack of marking, will cause the reader to cause a hazardous situation and, perhaps, an injury.
The first aggravation is believing that a marking error such as these, the existence of a “T” in the fuse designation, or the lack of an isolation symbol, will lead to an injury. But, we all know of famous incidents where lack of a suitable warning marking has indeed led to an injury, and the manufacturer was suitably punished. Because of these famous incidents, we feel obligated to correct the marking lest we subject our company to litigation.
The second aggravation is that changing a marking is both costly and time-consuming.
The third aggravation is justifying the change to management and other members of the organization. Since they are not familiar with the standard and do not understand the meaning of the “T’ or the isolation symbol, it is both awkward and difficult to explain why the marking must be changed, especially something as apparently minor as removing the letter “T” from the fuse designation or adding the isolation symbol.
The fourth aggravation is that some of us may consider a marking error as a reflection on our ability to do a good job. We failed to understand the standard, and we failed to do the job right as the marking we approved was found to be in error. Management and co-workers may consider such incidents when reviewing our credibility and performance.
The fifth aggravation is that our industry, safety of electronic products, impunes a great deal of importance to markings in terms of product safety.
The issue I want to address is whether such importance is justified. Can and do the markings required by standards contribute to the prevention of injury? If we
can answer this question, then most of the aggravations from markings will disappear.
Consider the following REQUIREMENT for multi-voltage input markings from a popular and successful IEC standard (my emphasis in capital letters):
“The voltage range SHALL have a hyphen (-) between the minimum and maximum rated voltages. Where multiple rated voltages or rated voltage ranges are given, they SHALL be separated by a solidus (I)”
This is INCREDIBLE! The implication is that the safety of the product will somehow be impaired if a hyphen or solidus is not used as specified. The standard presumes that it is THE AUTHORITY for the very best (least confusing) method of presenting power ratings data. (Rating markings are data; as data, such markings are not directly related to safety as are warning markings.) The requirement implies that there is no other method of presenting voltage data which could be better understood.
(This is not to criticize the possible need to standardize the presentation of rating markings outside of a safety standard.)
In this example, the focus is on voltage rating markings. The question is: What is the hazard if the user or installer fails to observe the voltage rating markings? Or is confused by the lack of a properly used hyphen or solidus? If the rating marking is required for safety of the product, then failure to heed the input voltage marking implies (1) that the equipment will be connected to an incorrect voltage, i.e., a voltage other than a rated value, and (2) that connection to such a value will render the equipment hazardous.
Is this reasonable? Many safety standards require an abnormal input voltage test for equipment rated for multiple input voltages. (Such a test is implied, but not overtly required by the safety standard which requires the hyphen and solidus.) If the equipment successfully passes the abnormal input voltage test, then whether or not the marking includes a hyphen or solidus is inconsequential to the safety of the equipment!
If a hazard should result from connection to an incorrect voltage, then a warning would be much more appropriate than reliance on the specified use of the hyphen and solidus. Yet the hyphen and solidus are required by the standard, and the certification house must require their use regardless whether the product is otherwise safe.
Here is another marking anomaly from the same standard. If a plug of an attached power supply cord is used as the disconnect device, then the installation instructions shall state that the socket-outlet in which the equipment is to be plugged shall be installed near the equipment and shall be easily accessible.
The implication of this requirement is that, if a hazardous situation should arise, disconnection of the equipment from the supply is the means to disable the hazard and render the situation as safe. For this to be effective, personal intervention is invoked, with the presumption that someone is always present in the equipment area when it is plugged in to the socket-outlet.
This flies in the face of safety construction and safety testing. The requirement implies that a hazard is expected whenever the equipment is plugged in, and that someone should be present whenever the equipment is plugged in.
I don’t know of any buyer of plug-and-socket connected equipment who, after purchasing the equipment and reading the markings would then call an electrician to move or install socket-outlet so that it was easily accessible
For the purposes of safety, we can classify safety markings into two kinds. The first kind is data, or information. The second kind is warnings, where personal intervention or personal avoidance is required as the means for assuring safety in a specific situation.
Rating markings such as fuse ratings and input voltage ratings are data. Data does not imply particular action on the part of the reader. Warning markings require a particular action, upon the event of specified conditions, for the reader either to intervene or avoid. For example, in the traditional fuse replacement warning, the condition is: “upon replacement of the fuse.” The intervention is: “use only the specified rating of fuse.”
By use of the words “personal intervention” and “personal avoidance,” I mean that a person must take a particular and specific action at a particular and specific time to avoid a hazard.
A good example to illustrate the concepts of personal intervention and personal avoidance in safety is that of driving a car on our public roads. We drive our cars using a set of rules of behavior, all of which allow us to predict the behavior of both ourselves and of other drivers in any particular situation. For example, the rule is to drive on the right side of the street. When we all do this, we are able to predict behavior. Driving on the right side of the street will avoid oncoming vehicles, will avoid collisions and will maintain our personal safety.
Driving without injury on our public roads requires specific personal intervention and personal avoidance actions at specific times. Understanding driving rules is accomplished by driver education and a test of individual knowledge. Conformation of understanding is the awarding of a license to drive.
Enforcement of driving rules is by means of a specific authority, the police, and by means of sanctions regarding the future operation of the car. The equipment manufacturer usually has no means to educate, test, or enforce behavior of persons installing or using the equipment.
Consequently, relying on personal intervention and personal avoidance as the means for safety is not reliable. Relying on data such as the presence or absence of a “T” in a fuse rating, or the presence or absence of an isolation symbol is unlikely to prevent an injury (although it may prevent product liability).
The safety of operation of an automobile relies on operator competence. The safety of plug-and-socket-connected electrical products relies on the hardware. Markings, whether data or warnings, do not make a product safe.
Richard Nute is a product safety consultant engaged in safety design, safety manufacturing, safety certification, safety standards, and forensic investigations.