Emerging Safety Standard

Oct. 22, 2010
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62368-1 safety standard

Three-block model

Safety three-block model

The demands of today’s consumers know no bounds when it comes to technology. Designers are increasingly challenged to create products that are not only innovative, efficient, and eye-catching, but also built and certified to the highest safety standards as well. This requires that safety standards keep pace with the new products and technologies constantly entering the market.

The evolution of IEC 62368-1 is an example of a safety standard that is keeping pace with, and perhaps outpacing, the market. Crafted specifically for audio/video, information, and communications technology equipment, this standard was developed based on the emerging safety testing protocol known as hazard-based safety engineering (HBSE). And while IEC 62368-1 won’t be mandatory until sometime during the second half of this decade, designers and manufacturers should start considering it now.

Birth of a Standard
As the 20th century closed, the convergence of technologies was only beginning. Quickly, distinctions between various electronic products were erased. Suddenly computers, audio/video equipment, and other information and entertainment technology became interconnected and interchangeable. Products originally designed for the office and shop came home, and children quickly mastered electronic gadgets long controlled exclusively by adults.

Up to this time, two International Electrotechnical Commission (IEC) technical committees shared responsibility for the safety standards for audio/video, information, and communications technology equipment. IEC TC74 developed safety standards for data processing equipment and office machines, while IEC TC92 covered audio/video and electronic equipment for household and similar use. In recognizing that the steady convergence of technology caused many products to fall into more than one category, the two committees were merged to form IEC TC108 (Fig. 1).

The new IEC TC108 technical committee was charged with developing a safety standard for consumer electronics, information, and communications technology equipment used in homes, offices, commercial, and other locations. The new standard would be based on the HBSE principles first formalized within Hewlett-Packard and introduced in an industry standard by ECMA, Europe’s prominent computer industry association. The standard would be supported by sound engineering principles, research, and field data.

TC108’s goals for the new standard included developing one that would cover a broad range of products, clearly identifying the hazards addressed, and allowing for the minimization of regional and national differences. It would be equally important to achieve these benchmarks in a user-friendly manner.

The Fundamentals
Generally, IEC 62368-1 is a performance-based standard, with requirements developed using HBSE. Specifically, the user identifies the potentially hazardous energy sources and then identifies and qualifies safeguards necessary to mitigate them and produce a safe product. Performance-based requirements, as opposed to prescribed constructions, offer flexibility when considering new technology. The standard provides safe limits for various types of energy sources but doesn’t necessarily specify how to achieve those limits. For some applications, proven construction options are also stipulated as an alternative compliance option. 

New terminology is an essential element of IEC 62368-1, in part to align it with HBSE concepts, and also in part to differentiate it from traditional safety standards for other forms of electronic equipment as well as from the standards it replaces. The term “safeguards,” not previously used in this context, is prominently featured. Similarly, “energy sources” are identified and classed, e.g., Electrical Energy Source Class 1 (ES1), which combines safe voltage and current limits under one definition and replaces the terms Safety Extra Low Voltage (SELV) and Limited Current Circuit (LCC), used in previous standards.

Notably, individuals previously identified as either “users” or “service persons” are known under the new standard as “ordinary persons” or “skilled persons,” while “instructed person” refers to an individual who is expected to interact with the energy source safely while under the instruction or supervision of a “skilled person.” The type of person intended to interface with the product typically dictates the type, numbers, and forms of safeguards required.

The Three-Block Model
One of HBSE’s underlying principles essential to IEC 62368-1 is the three-block model, which represents the relationship between a potentially hazardous energy source and pain and injury resulting from it. Under this scenario, the energy source capable (Fig. 2) of causing the pain or injury will only do so if there is a transfer of energy to a body part.

The new standard identifies several types of energy sources that can be represented by the three-block model including electrical, thermal, kinetic, and radiated energy. The energy sources themselves are further divided into three classes, e.g., ES1, ES2, and ES3. These classes are based on the magnitude and duration of the energy emissions.

To prevent pain or injury, either the energy source can be designed to levels incapable of causing pain or injury, or safeguards such as insulation can be designed into the product to prevent the energy transfer to the body part. This represents the new standard’s three-block model for safety (Fig. 3), which suggests that if a suitable safeguard is inserted between the energy source capable of causing pain or injury and the body part, there will be no injury.

IEC 62368-1 also employs the three-block model in the context of electrically caused fires. This condition results from the conversion of electrical energy to enough thermal energy to cause a fuel material to ignite. As with the previous model, in order for this to happen there must be an actual transfer of energy from its source to the fuel material itself via conduction, convection, or radiation.

Similar to the pain and injury scenario, safeguards such as thermal resistance or a fire enclosure can be designed into a product to reduce fire risk. If adequate safeguards are in place per the standard’s prescriptive safeguard requirements, the risk of fire will be reduced to acceptable levels.

Stepping Up to the New Standard
While IEC 62368-1 won’t be mandatory until later this decade—and despite the uncertainty expressed by some product designers regarding its potential impact on creativity and production schedules—there is growing industry support for implementation of the new standard in the next few years. An extended period of transition acknowledges that suppliers of IT and audio/video products will need time to process and adapt the new concepts and requirements. This period will also enable manufacturers, suppliers, test houses, certifiers, and safety engineers to learn and apply the new requirements and deploy the appropriate test protocols and documentation.

UL’s Engagement with IEC 62368-1
IEC 62368-1 ultimately will serve as the single standard for products covered under its scope while eliminating differences in requirements and shortening products’ time to market. Underwriters Laboratories (UL) has played a significant role in the development of IEC 62368-1, directly within TC108 and through leadership and participation in various National Committees. UL is supporting the transition to IEC 62368-1 through the development of informational and educational materials. We also are reviewing IEC documentation, preparing for a North American version, and developing a new generation of HBSE material called Applied Safety Science and Engineering Technology (ASSET).

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