Theory of a design goal:

Product Safety

  1. Risks related to products
  2. Research Methods
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Risks related to products

Among the goals for the design of products, the target of avoiding danger and risk of injury to the users and other people is universally accepted as more compelling than other goals of design. This is understandable because the damage to the user that can follow of substandard safety of a product can sometimes be loss of life or limb. Also the consequences to the manufacturer are often graver than those that can ensue from inferior standard concerning other properties of the product (like its usability, beauty etc). In most countries the manufacturer is held responsible for any injury caused by the product that the user cannot easily foresee. Sometimes, but not always, the manufacturer can avoid the responsibility by effectively warning the user of the risk. The responsibility can include indemnity liability to the person that has suffered damage.

Recent development of legislation in the U.S.A. and Europe have further heightened the importance of taking care of the safety of products. This is because the principle of strict liability is gaining ground in the laws and judgements in these countries. Under strict liability the injured person needs no more prove negligence of the designer; he or she needs only to show that a defect in the product has caused an injury. It will then be the responsibility of the designer and the manufacturer to show that they have taken reasonable care to protect or warn the consumer. The principle of strict liability has been adopted in the U.S.A. since 1963, in the United Kingdom since 1978, and lately in several other countries of the EU. Cf. Abbott (1980) pp. 13...52.

The most important risks of injury related to products are the following:

Risks of Breaking and Collapse

If a product breaks down, it means that not only its usability ends, but its broken parts can also involve a physical danger to the user or to other people nearby. The larger and heavier the product is, the greater the risk. Buildings, ships and other vehicles are examples of this.

On the other hand, from the viewpoint of the user and especially of the manufacturer it is desirable that sufficient sturdiness and stability is attained with minimal use of material, weight and cost. It is therefore appropriate that the use of materials is optimised with the help of exact algorithms for the calculation of stability. This has already for centuries been the case with buildings, the design theory of which is described elsewhere under the title of Theory of Building Construction. This theory, of course, is based on extensive research including experiments on the strength of building materials (see below). Even the governments of most countries have judged the question so serious that they have issued detailed regulations on the stability and safety of buildings, ships, aeroplanes, cars and other such large products.

Harmful Materials and Ingredients

It is self-evident that food and beverages must not contain harmful or doubtful ingredients in larger quantities than is prescribed by national health officials. These agencies, as well as international organizations like FAO base their regulations on statistics and research on public health.

Other products are not supervised so definitely as food, but at least those products that come in near or prolonged contact with people should be free from toxic paints, asbestos and other detrimental substances. This is especially true for toys that small children can suck and gnaw, likewise in containers and utensils for the preparation of food.

For highly toxic materials there is no theoretical problem: they must be prohibited and the proscription must be controlled, perhaps by the government. However, there are many materials that are harmless in small quantities and at the same time useful ingredients in industrial products. If no governmental recommendations or standards can be found, the manufacturing company has perhaps to determine this tolerable limit with chemical and physiological research.

Electrical Dangers

The main target is simply that nobody should ever risk getting an electrical shock from the mains circuits. However, it is difficult to prevent people from using electrical appliances precariously, like using hair dryers in wet bathrooms. What the researcher can do is to study the statistics of accidents and try to conceive improvements to existing appliances that would have prevented the recorded accidents. For example, it has turned out that a residual current device (ground-fault circuit-interrupter) can protect the user against electrocution if a hair-dryer falls into water when the switch is "on". Indeed, many manufacturers have now agreed on a voluntary standard where this refinement is specified.

Much the same approach can be applied for reducing the risks related to the use of gas in heating and cooking.

Mechanical Dangers

Mechanical dangers result mainly from sharp edges and mobile parts of machines. There is also the risk of excessive heat which can occur in energy-intensive apparatus like heaters, cookers and dryers (of hair or clothes, for example).

Particularly suspect are power tools, which have also already long been crucial objects in occupational health and safety studies. There are a number of internationally accepted standards that specify how the dangerous parts of tools like cutting blades should be protected.

Another group of mechanically hazardous products are playground and sports equipment like trampolines and bicycles.

It is difficult for the designer to circumvent all mechanical dangers which can occur in the use of the product because the risks depend very much on the way the product is used. Accordingly, it is difficult for the researcher to write guidelines for designers. Something can, nevertheless, be done by studying the published statistics and records of accidents, observing how products factually are being used, and by considering the list of critical questions typically used in Methods Engineering.

Fire Hazard

In buildings and vehicles the techniques to reduce the hazard of fire resemble the risk of collapsing, discussed above. The methods of reducing the risk are similar and effective, too, because building fires are usually recorded together with the causes of ignition, fire brigades can easily be consulted, and in most countries there are special laboratories suitable for experimentation with fire.

Most people would not like the idea that only non-burning materials were allowed in buildings and vehicles, so researchers and designers have to aim at compromises between fire safety, habitability and cost. Some of these arbitrations are then transferred into governmental regulations, voluntary standards of industry, and other guidelines of design.

Furniture often contains burning material. In the United States, cigarette-ignited upholstered furniture fires kill more people every year than any other kind of fire. The number could be cut down if furniture makers would use fabric that is more resistant to cigarette ignition. Indeed, researchers have through experiments in fire laboratories pointed out such fire-proof fabrics which many manufacturers then have started using.

Smaller products entail different problems of fire. Inflaming can occur in any equipment which uses energy if the cooling is restricted by dust, for example. This happens often in older TV sets and clothes-driers, but since then experience and research has teached the designers to improve the ventilation.

There are also products that are inherently inflammable like lighters, fireworks and explosives. For all these can be said the same as above: the risk depends on the way the product is used. Observation of how the product is used, and the list of critical questions can help. It is possible that research cannot improve the designs of these products; in such a case you can at least consider rewriting the instructions for the use of the product.

Accidents to Small Children

Most accidents to small children occur in contact with the normal elements of the home: falling on the floor from chairs, tables or step-ladders, tumbling in the stairs or on carpets, tipping a hot water kettle, playing with doors, windows, tools, knives, bottles, tin openers, nails, air-tight bags etc. For many of these products it is impossible to reduce the risk of accident either by modifying those products or by avoiding their presence in the home.

Nevertheless, sometimes it is possible to revise the product so that a small child cannot easily get hurt when playing with it. For example, there is the risk of small parts or pieces of toys, furniture and other products used in homes which can become detached and which a small child can then try to swallow. This risk can be minimized by avoiding loosely fastened small parts in products intended for family use.

Another example is the kitchen stove. The more recent models are often equipped with optional devices which prevent opening the oven or turning power on too easily. Often these mechanisms can be disabled for those families which include no small children.

Accidents to the Elderly

Old people often have difficulty in moving themselves. Many of them are using a wheelchair or other device which, however, sometimes fails to give support and an accident ensues. Reaching things on high or low shelves is often difficult, and accidents happen when an aged person uses a stepladder in order to reach a high cupboard, especially in the kitchen. Besides, the elderly often have reduced abilities of sight, hearing etc., which increase the risk of accident. Many of the dangers can be diminished easily by proper design of buildings and furniture.

Another common cause of accidents to old people is absent-mindedness, for example forgetting to turn off heaters and kitchen ranges. These risks can be reduced with "smart home" technology, in other words automating some mechanisms in the home, for example introducing thermostats, automatic cut-off of kitchen stove, automatic timing of lighting, locking and unlocking of doors, simplified telephoning etc.

Research Methods

Each type of risk is different and it can call for some specific methods in its study, but there are also a few generally applicable approaches in the study and prevention of accidents. A few usual approaches can be defined on the basis of the immediate target of the study:

Below each one of these approaches is being discussed.

Descriptive Research of Accidents and Risks

Possible sources of data on accidents related to industrial products include:

Public statistics of accidents are collected in many countries by the government or by a public institution. Besides, all countries have official statistics of deaths which indicate also the death causes at least summarily. In some countries the insurance companies make at least part of their statistics available to the researchers, too.

The problem with statistics concerning accidents is that they do not contain all those details about the incidents that the researcher would need. The technique of Ex Post Facto Research can only clarify relationships between those variables that the existing tables contain. For example, from the statistics of deaths you can calculate the contingence between the victim's age and the cause of death.

Failure rate If the researcher wants to know the circumstances of the incident accurately, and if the names and addresses of the people involved in the accident are known, there is the possibility to ask supplementary information by employing Thematic Interview. Even polls have been used, but then the researcher must have an exact hypothesis about what he is going to study already at the beginning of the project because new, surprising factors would be difficult to deal with in the questionnaire method.

Complaints from the customers and feedback from the after-sales service of the company are discussed elsewhere, under the title of Feedback and Critique. Usually they are most frequent and the company's interest in them is at highest in the running-in phase of a new product (see the "bathtub curve" on the right, from Abbott, 1989 p. 127) when "children's diseases" in a new product are most likely to occur and the company is still prepared to adjust the design of the new product before the manufacture starts in a large scale. However, it would usually be wise to gather and save all the feedback that the company can get, because it can later become an invaluable source of ideas when designing the next generation of products.

Design Theory

Developing design theory Design theory includes several kinds of relatively permanent (i.e. not project-specific) information that the designers can use as the basis of their new designs. It is the task of researchers to provide such information, compress and publish it in formats that are convenient for designers.

Though safety is a universal and essential requirement, its exact content depends on the context. For example, the risks to buildings because of earthquakes are different in various countries. The requirements of health depend very much on local climate, electrical safety on the local mains voltage etc. For this reason many requirements concerning the safety of products must be written separately for each country, which means that they are often given as governmental regulations. These usually stake out the allowable limits, minimal or maximal, of the safety-related attributes of products, but do not otherwise restrain the design. Even national jurisdiction on the highest level has sometimes been used, for example in the United States the Federal Refrigerator Safety Act has already for the past forty years required that refrigerators be capable of being opened from the inside, to prevent children from being trapped.

Another usual channel of publication for design theory concerning safety are standards, especially those that have national validity and more and more often also international ones. They can be either compulsory or voluntary, and confirmed on various levels from international organizations to private companies. Voluntary standards are often developed as joint projects of the major manufacturers of a certain product in a country. Examples of these are the requirements for upholstered furniture that the furniture manufacturers in the United States have defined in order to reduce the hazard of fire.

When developing the instructions for future designers, the procedure explained in Preparing Design Theory can be used. The starting point is a known or felt shortcoming in the questions of safety, for example an alarming rate of accidents of a certain type.

The researcher's task when defining an acceptable level of safety will often be easier than preparing some other recommendations for design, because the demand for safety tends to dominate the others and it is not likely to get in conflict with other goals of design (like e.g. usability or ecology) and the researchers of safety need not often trouble themselves with finding compromises between several contrasting goals.

The target of economy sometimes gets mixed up in the study of safety. This does not mean that anybody would want to calculate the price for a saved or lost human life. Nevertheless, the resources are seldom unlimited, and it can be meaningful to focus them where most lives can be saved. Often there are alternative ways of reducing the risk of accident and the costs are different. Often it also turns out that the first, simple tactics for reducing a certain risk are relatively cheap, but the decisive manoeuvres which would cut the risk to zero would be immensely more expensive or they would have other disadvantages.

When we speak of such accidents that involve only material losses and no injury to people, economic optimization can well be used. On the level of a nation it is possible, for example, to compare the total yearly costs of a certain type of accident to the total expenditures that are used to prevent this type of accident. Some usual models for optimization are explained under the title Normative Study of Economy.

The regulations and recommendations of design theory should be tested in practice, too. Often an efficient method is to co-operate with a few companies that are producing the products in question. When test persons are needed, these should be selected from the population that the regulations are expected to protect, which often is the same as the population of the country. When appropriate, you should include a few children, old-aged people and other people with reduced abilities, cf. Weighted random sample.

The margin of safety is a question that has to be considered when writing the instructions for designers. If tests show that in 100% of the studied cases the risk of accident has been eliminated, is it enough? Must we be prepared for the case that the product is treated exceptionally, or contrary to the instruction book? Should we try to prevent absolutely all accidents, or are there tolerable accidents? The researcher can have own opinions on this type of questions, but in principle the answers should be gathered from a larger public. Cf. a checklist of typical interest groups in a development project.

The forum of publication of the proposals which have been developed needs some attention in order to reach the right audience and maximize the practical outcome. If the project has been launched by voluntary co-operation of manufacturers, these obviously already have mutual channels of information which can transmit the results of the study, too.

Product Development

Depending on the starting point of product design there are two slightly different approaches to the questions of safety:

  1. Products which are explicitly designated for safety purposes like helmets or goggles.
  2. Products which potentially can be dangerous and shall be designed with safety in mind.

1. Products designated for safety purposes. Here the principal goal of design is safety. It constitutes a major point already in the first product concepts, when preparing the proposals and when evaluating the proposals.

An example of designing a new product with is aimed at lowering the risk of accidents is Sirkka-Liisa Keiski's project (1998) for developing a new type of fixed furniture for kitchens. She first interviewed and observed a group of old aged people in their home kitchens and found that many accidents happen because old people that move uneasily are trying to get or put things on shelves that are placed too high or too low. She concluded that kitchen cupboards must be designed wholly anew with the storage space on a more convenient height. Moreover, the height of table tops should be adjustable, especially considering the needs of people using wheelchairs.

Next Keiski constructed a mock-up kitchen on these principles, tested it with old persons and improved it during repeated observation and interview sessions. A photo of the mock-up.

2. Products which are potentially dangerous. Product development Most projects of new product development start at defining the future use of the product and its other desirable properties, and safety comes into picture first when the product proposals are being evaluated from various viewpoints which include safety among others. During the development project the proposal will normally be improved and the evaluation has to be done repeatedly as long as the design proceeds, and therefore the typical product development process can be likened to a spiral where the phases of analysis, synthesis and evaluation repeat like in the figure on the right.

Evaluation of future risks of accidents can be meaningful only if there is a realistic assumption about who is going to use the product, because the safeguards and warnings must be dimensioned accordingly. A baby, a young child or a geriatric will need more protection than a deep-sea diver, as Abbott (1980) p. 109, puts it. The target customers should therefore be defined early in the design process. From the safety viewpoint it would be desirable to have also an idea about those other people beside the customer who can possibly use the product or who can be present (e.g. the children in the family).

Likewise, the environment of using the product can affect the risks. The product specification should indicate the assumed extremes of relevant ambient characteristics like brightness, temperature, rain, dust, noise etc.

When enumerating the requirements for the new product, it is advisable to put the most compelling viewpoints on safety into a separate list which contains only the obligatory requirements that the new product must meet. In this way the requirements of safety do not get mixed up with other, voluntary targets of the project which often have to be arbitrated with the help of cost-benefit analysis, for example.

Once the first mock-ups of the future product are created (cf. Presenting the Draft and Prototype) it will be possible to start testing them from the safety viewpoint, and as soon as more detailed prototypes become available, these should again be tested. You should select the test persons so that they are not too different from the target group of customers. When appropriate, you should include a few children, old-aged people and other people with reduced abilities. When testing the use of a product, suitable methods often can be adapted from Non-systematic Observation and Methods Engineering.

The test situation in laboratory gives usually too favorable a picture of the risk of accident because people are using the product strictly according to the instructions. In real life, products are often used and misused in ways that the designer could hardly expect. Abbott (1980) p. 110, gives the following situations, among others, that should be kept in mind when designing safeguards:

Remember, finally, that the instructions for use of the product are very important from the viewpoint of safety. They should not be made in the last moment, and they should be tested, too.

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August 3, 2007.
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Original location: http://www2.uiah.fi/projects/metodi