Zero risk concept

Total safety, ie, no risk, is not a reality. As stated by Mercier [1] a zero-risk concept has the appearance of supporting a generation s unreasonable wish to live forever . Even an essential chemical such as water in hazardous situations, eg, drowning, is not safe, and if ingested in excessive quantities, ie, 30+ 1 d, will cause kidney failure. Oxygen, essential to all mammals, if inhaled at excessive concentrations can result in injury caused via free radical mechanisms. 

The zero risk concept produced the greatest growth area for analysts in the history of mankind. New methods had to be developed, limits of detection had to be lowered, and compliance had to be demonstrated. All this was fueled by the linear extrapolation to zero. 

The precautionary nature of risk management decisions made by public health authorities can approach a zero risk tolerance that is not based on the outcome of the risk assessment process or the certainty of the data that underlie the assessment process but rather on social and political influences. The original purpose of risk assessment was to separate important from less important risks and provide a basis for making decisions to protect the public health. With the adoption of risk assessment and risk management as a process for making public health decisions, the concept of achieving zero risk for suspect carcinogens was abandoned as a workable, achievable policy. 

What is now essential is to derive the knowledge to decide the safety of these substances and to answer the question — how safe is safe enough The costs entailed in producing a risk-free society would be so great that few benefits would remain and, the concept of zero risk means that one has a desire to live for ever. 

Those famiMar with the concepts of risk understand that attaining zero risk is impossible and that a predictive measurement system that can identify every possible risk on an anticipatory basis has not yet been developed. Furthermore, I believe we have to admit that we are not good yet at having developed measurement systems to determine whether cause-and-effect relationships exist for the safety interventions we propose. 

Crosby s Zero Defect concept is based on the fact that two things cause mistakes lack of knowledge and lack of attention [1]. Lack of knowledge can be measured and attacked by tried and true means. However, attention is a state of mind. It is a preconceived attitude (at-risk behavior) that must be changed by the individual (employee) [1],... 

It has long been recognized that a zero risk level is not attainable. If a facility exists or an activity proceeds, it is not possible to realistically conceive of a situation in which there is no probability of an adverse incident or exposure occurring. William W. Lowrance was one of the most significant and influential authors on the concept of acceptable risk. Lowrence (1976) writes in his previously dted book Of Acceptable Risk Science and the Determination of Safety that ... 

Hazard addresses only the severity or end result. Risk combines the concept of severity of the accident consequence and the likelihood of it occurring. In the simplest terms, risk is the combination of the probability (or frequency of occurrence) and consequence (or severity) of a hazard. There are always risks. There is a risk staying in bed and a different risk getting out of bed. As much as we would love to have zero risk, that is a practical impossibility. Because we cannot totally eliminate risk, we try to shrink it as much as possible. Lowering either the probability or the severity of the hazard or both can do this. So... 

The concept of human error became part of safety lore when Heinrich noted that as improved equipment and methods were introduced, accidents from purely mechanical or physical causes decreased and (hu)man failure became the predominant cause of injury. This assumption became the second of the five dominoes in the famous Domino model, described as fault of person. This is in good agreement with the philosophical and psychological tradition to treat human error as an individual characteristic or a personality trait. A modern example of that is the zero-risk hypothesis of driving, which proposes that drivers aim to keep their subjectively perceived risk at zero level. 

Specificity—Saying that a method is specific means that it is exclusively dedicated to one or several analytes. In terms of quality, specificity minimizes the risks of dosing a wrong molecule. Note that the concept of zero risk does not exist in analytical chemistry. The characterization of the analyte is based on strict criteria. 

The US-EPA (1986) applied the concept of response addition to the determination of cancer risks, assuming a complete negative correlation of tolerance. This assumption is considered to contribute to a conservative estimation of risk, since the correlation of tolerances may not be strictly negative in inbred homogenous experimental animals. There is a major difference between the concepts of response addition and dose addition when the human simation of low exposure levels is assessed. Response addition implies that when doses of chemicals are below the no-effect levels of the individual compounds (i.e., the response of each chemical equals zero), the combined action of aU compounds together wdl also be zero. In contrast, dose addition can also occur below the no-effect level and the combined toxicity of a mixture of compounds at individual levels below the no-effect level may lead to a response. 

Here is an appropriate place to discuss Richard Hills s important and influential reconstruction of Watt s route to the separate condenser.66 Hills presents the concept of the perfect engine as the guiding idea here. His account runs the risk, in my view, of assimilating the concept to proto-thermodynamic physical ideas. I want to argue that for Watt in 1769 preventing the waste of steam, reducing it theoretically to zero, was conceptualized chemically, but first let me set out briefly what I take to be Hills s argument. 

The concept of risk is a valuable tool to make responsible and scientifically sound decisions. By definition risk is never zero. It must be balanced by a benefit to make it acceptable. 

Before I proceed, we must ask whether the idea of honor involved here is the same as the one 1 gave earlier. The behavior of Meidias fits well with the definition of honor as an attempt to inflict damage on another at some cost or risk to oneself. Slapping someone in public is a paradigmatic case of struggle between equals for the purpose of gaining honor at the other s expense. Meidias took a risk and in fact had to pay a cost (he paid Demosthenes to drop the case). Other cases, which do not involve equals, are more puzzling. They do not involve honor as I defined it moreover, there docs not seem to be any plausible concept of honor in which these interactions had a zero-sum nature. 

Various mathematical models have evolved that attempt to incorporate some of the biological concepts and hypotheses. Some of the most commonly used models are the Probit, the Multi-Hit, the One-Hit, the Multi-Stage, and the Weibull. All of these models have the defined property that for zero dose, the risk is zero. However, since the spontaneous background incidence is not zero for most tumors, the models incorporate background, utilizing the concept of independence as ascribed by the correction of Abbott (14) i.e.,... 

A concept that threads throughout this book is that of inherent safety. The basic idea is that, were a system to fail, it would end up in a safe state regardless of the existence and effectiveness of safeguards. (The term inherent safety is actually a little misleading. Risk can never be zero, and perfect safety can never be achieved. Hence the term inherent/y safer is probably a better choice.)... 

If the residual risk for a task or operation is never zero, for what risk level does one strive At best, we can say that the concept of designing and operating to attain risk levels as low as reasonably achievable or practicable should be applied to the situation being considered. 

Many studies have shown that there are many factors that can be chosen as risk factors that increase the probability of accidents to occur and their severity. The correlation between any factor and road accidents means that they both increase and decrease simultaneously. For example, if an increase in speed causes an increase in road accidents it means both are correlated. The degree of such a correlation differs from factor to factor and is usually measured by using different statistical techniques and it ranges from zero to one. If one, it means the factor is highly correlated to road accidents and if zero there is no correlation at all. In this section I will not discuss these techniques in detail, but instead I focus on the results from several sources have been reviewed. I have tried to select recent studies demonstrating long international experience in this field. For example, the Handbook of Road Safety Measures (Elvik Vaa, 2004) provides a wide literature survey and meta-analysis of different road safety measures made in relation to accidents in different countries. I will provide a summary of the most important factors in relation to risk, exposure and consequences at the end of this section. However, I know that it is hard to identify all those macro-factors that have the potential to contribute to accident occurrence and consequences. In all approaches, the chosen factors should be relevant to the concept of road safety that one is seeking to measure. 

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