Product safety, acceptable risk levels

Regularly at safety conferences and in the work of committees drafting safety standards, controversy develops over the level of risk that is acceptable. This chapter presents a thought-provoking review of the levels of risk acceptable in various enterprises (space travel, auto racing, various manufacturing and business entities) and for product safety. It also provides a practical, useable framework for safety practitioners to use in determining acceptable risk levels. 

A convincing statement is made, as in the following excerpt, about the need, sometimes, to go beyond issued safety standards in the design process and to have decisions on acceptable risk levels be based on risk assessments. This excerpt is taken from Related Information 1— Equipment/Product Safety Program, which is an adjunct to SEMI S2-0706, Environmental, Health, and Safety Guideline for Semiconductor Manufacturing Equipment. 

If the residual risk for a task or operation cannot be zero, for what risk level does one strive It is the norm that resources are always limited. There is never enough money to address every hazard identified. Such being the case, safety professionals have a responsibility to give counsel so that the greatest good to society, to employees, to employers, and to the product users is attained through applying available resources to obtain acceptable risk levels, practicably and economically. 

It is recommended that safety professionals use actual cases in which they are involved to support the premise that addressing hazards and risks in the design and redesign processes will result not only in achieving acceptable risk levels but also higher productivity and operational efficiency. That may be done easier in the redesign process. This author says the following to safety professionals ... 

In applied system safety, the emphasis is on having acceptable risk levels designed into systems before actual production or operation of a system. 

It is vital to distinguish between technical safety and reliability. A machine s safety level significantly depends on the required responsibility of a producer for their product, in terms of the European Union and specific national legislation. In most of the cases, drafted measures to increase machine safety also influence its reliability. Quantitative safety assessment is executed by estimating or calculating the risk, whereas its acceptable level is defined by the value of its acceptability. Risk utilization for safety assessment of the machine s construction requires... 

Promotion of the quality of life. The setting of standards of safety implies the definition of what is acceptable as a reasonable level of risk in the foreseeable use or even misuse of a product. Safety aspects play a very important role in current standards work. 

Many risks people are subjected to can cause health problems or death. Precautions should be taken based on what is practical, logical, and useful. However, those involved in laws and regulations, as well as the public and, particularly, the news media, should recognize that there is Acceptable Risk. This is the concept that has developed in connection with toxic substances, food additives, air and water pollution, fire and related environmental concerns, and so on. It can be defined as a level of risk at which a seriously adverse result is highly unlikely to occur but it cannot be proven whether or not there is 100% safety. In these cases, it means living with the reasonable assurance of safety and acceptable uncertainty. This concept will always exist. Note the use of automobiles, aircrafts, boats, lawnmowers, food, medicine, water, and the air we breathe. Practically all elements around us encompass some level of uncertainty. Otherwise, life as we know it would not exist. Many products and environmental factors are not perfect and never will be perfect. 

Since the meaning of safety varies between individuals and depends on our point of view, I have purposely left the definition of safety till the end. With a thorough knowledge of safety, we can now answer the question that has been the topic of many discussions, What is a safe product The General Product Safety Directive defines a safe product as any product which, under normal or reasonably foreseeable conditions of use does not present any risk or only minimal risks compatible with the products use, considered as acceptable and consistent with a high level of protection for the safety and health of persons. Also, as stated in the Product Liability Directive, a defective product is one that does not provide the safety which a person is entitled to expect, taking all circumstances into account. ... 

The government agency (or other procuring organization) for whom a system (or product) is being developed must determine the objectives and specifications for the project. The specifications should include standards of safety performance and define the levels of acceptable risk. The specific system safety tasks and requirements must also be defined. 

Design for Minimum Risk The system safety order of precedence dictates that, from the first stages of product or system design, the system should be designed for the elimination of hazards, if possible. Unfortunately, in the real world, this is not always practical or feasible. If an identified hazard cannot be eliminated, then the risk associated with it should be reduced to an acceptable level of hazard probability through design selection. 

Whatever your decision may be, it will help to remember that ancient Chinese proverb If you don t know where you are going, then any road will take you there A properly implemented and managed system safety program can provide an excellent roadmap to help individuals, organizations, and entire corporations find their way to a safe, productive, and profitable destination while ensuring the lowest possible level of acceptable risk with a maximum return on investment. 

Furthermore, safety professionals need to understand that decisions made with respect to risk acceptance or reduction may not always be based on logic. Sometimes, workers have perceptions about risk levels in a given situation that are unrealistically high. Although their perceptions may not be well founded, they have to be addressed in an attempt to diminish their fears. Companies have found that spending a little money to counter unreasonable perceptions of risk may be a good investment if employees are relieved of their fears and production slowdowns or interruptions are avoided. 

In practice, however, we found a number of difficulties with this structure. The first is that a safety process is complex, involving many stages. Unless it is very carefully captured and maintained, product-structured evidence may not provide sufficient information to demonstrate that all the steps of the process have been followed. Consider, for example, a product safety argument that the risks presented by all identifled hazards have been reduced to an acceptable level. The top few levels of such an argument structure are shown in Figure 7. If we also want to demonstrate that a classical safety process has been followed, we may want to complete a structure such as that shown in Figure 8. 

The SHA assesses the safety of the total system design by evaluating the integrated system. The primary emphasis of the SHA, inclusive of hardware, software, and HSI, is to verify that the product is in compliance with the specified and derived SSRs at the system level. This includes compliance with acceptable mishap risk levels. The SFLA examines the entire system as a whole by integrating the essential outputs from the SSHAs. Emphasis is placed on the interactions and the interfaces of all the subsystems as they operate together. 

The safety/risk criteria. The safety/risk criteria establish the top-level system safety requirements, or objectives. Regulatory authorities may have different definitions for the various categories of hazards/accidents. To be able objectively to distinguish and evaluate the various hazards present, it is important to define the exact terminology and to allocate a measure of performance. This is an important (and arguably most neglected) topic as it is the safety acceptance criteria the system is expected to achieve, and hence the measure (or standard) the assessment will compare the system against. For more detail on safety criteria, see Appendix B. The system level. Define the systems level at which safety is to be assessed. The importance of this step is explained in Section 8.3 above. A safety assessment by a supplier of a component (e.g. a flare dispenser) will vastly differ in scope and approach to a safety assessment for a product (e.g. an aircraft) or user system (e.g. a facility). 

After obtaining the prototypes, tests must be made to determine the utility. Generally these include a short time destructive test to determine the strength and to check out the basic design. Another test that is done is to use the product in the projected environment with stress levels increased in a rational manner to make for an accelerated life test. Other tests may include consumer acceptance tests to determine what instructions in proper use are required, tests for potential safety hazards, electrical tests, self-extinguishing tests, and any others that the product requires. In the case of high risk products, the test program is continued even after the product enters service. 

Because of the requirement by public health authorities that any chemical used in the production of food should pose no risk to the consumer, the safety of food chemicals has mostly been approached from the perspective of whether or not the chemical poses a toxicological hazard. If it does so then it is argued that it is likely to present some degree of risk to the consumer even if humans are exposed to very low levels of that chemical in their diets. However, if exposure is minimal, depending on the nature of the toxicity, it is likely that the risk is acceptable because it is so low. What is not considered, or even tested in the experimental systems designed to study the toxicological effects of chemicals, is whether there are levels of exposure where there might be potential health benefits. The assumption is made that any nonnatural, adventitious substance that can be shown to be toxic is unlikely to have health benefits. 

As a basis for the determination of risk it must be assumed that the colorants are properly handled and applied. It is not appropriate to estimate risk primarily on the basis of exposure values obtained under improper working conditions, or where appropriate plant and equipment are not available. Ensuring satisfactory operating conditions and training of operatives to handle products correctly is essential nowadays for technological success as well as for health and safety requirements. In this way, exposure levels can be kept below the threshold of unacceptable risk. It is reasonable to accept that for practical purposes levels of exposure exist below which the risk becomes trivial [67]. 

The chlorinated chemicals assessed do not have the same risk profile. For the more volatile chemicals the safety margins between the actual exposure and the level at which no effect on the environment would be expected is quite high. For more persistent chemicals there is a need to look to the environmental compartment where they can be accumulated (mainly in sediments and biota). For some of these chemicals the safety margin is quite low and in worst-case situations serious effects may occur. For the very persistent, bioaccumulative and toxic chemicals (like dioxins, PCBs and DDT), acceptable environmental concentrations are so low and difficult to control that the industry is committed to reducing as far as possible releases to the environment through application of Best Available Techniques (BAT), mainly with respect to dioxins. For other chemicals (PCBs, DDT), production has already been halted for some years. 

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