Acceptable risk, and safety

Jeff is a talented Staff Engineer employed by a major chemical plant in West Virginia he has a solid background in Loss Prevention. Jeff Josecks article was written to spark interest and discussion of process safety in safety meetings. It is also very skillfully worded to spark the readers into thinking about acceptable risks and minimal risks. 

The German model was developed with a goal to determine the nature of any special risks and safety precautions for the protection of workers handling pesticides as required by Council Directive 91/414/EEC. To comply with this Directive, exposure estimates must be compared to tolerable (acceptable) exposures for the relevant use scenarios and the active substance (active ingredient) under consideration. 

Love Canal also contributed strongly to the development of risk assessment methodologies since the Superfund Act required that determinations of clean-up levels be made based on a scientific assessment of data on the toxicity of contaminants found at the hazardous waste sites and the potential for exposure to those contaminants. In light of the limitations in available knowledge, new approaches had to be devised to answer the question of how clean is clean The methodology that was adopted married scientific data to value judgments about acceptable risk and margins of safety. This approach remains in use. 

Top-level criteria and requirements are defined primarily from two sources the regulator, whose concern is primarily public health and safety, and the user, whose concern is all encompassing (e.g. safety, performance, availability, and economics). Each of the four Goals has been quantified by a series of top-level criteria and requirements (Ref. 1, 2). The Top-Level Regulatory Criteria are a necessary and sufficient set of direct quantitative statements of acceptable health and safety consequences (doses) or risks to the public that are independent of reactor type and site. Demonstration of... 

Top-level regulatory criteria should be a necessary and sufficient set of direct statements of acceptable health and safety consequences or risks to individuals or the public. 

In the six years since the second edition of On the Practice of Safety was published, several developments have taken place that require or propose that hazards be recognized and analyzed in the design process and that risk assessments be made toward achieving an acceptable risk level. Safety practitioners—pay attention. Comments on some of those developments follow. 

The ALARP principle is often applied, involving a safety goal with a hmit (maximum acceptable risk) and an objective (broadly acceptable risk). 

Pipeline gas transport is connected with creation of cover ruptures and accidental gas ignitions. To minimize impacts of breakdowns it is necessary to have a pipeline safely zone, which size determines the Czech act No. 458/2000. In some cases it is possible to decrease this zone, but in other cases it is necessary to increase this zone (parallel pipelines, gas reservoir, etc.). New safety zone range should be estimated with due regard for acceptable risk level. Safety zones evaluation framework consists of all risk category tasks except societal risk modelling. Thus we consider 1st, 2nd, 3rd, 4th and 5th task category. In some cases we don t include economic damages. 

After a series of interactions between the different parts of NASA s distributed knowledge system, what began as an out-of-family event was eventually categorized as an accepted risk and no longer a safety of flight issue. As the shuttle re-entered the Earth s atmosphere on February 1, hot plasma breached the RCC tiles and the shuttle disintegrated. The CAIB report said ... 

Although the prevention through design standard applies to occupational hazards and risks, the previously given definitions of acceptable risk and ALARP apply to all hazards-related exposures (fire protection, transportation safety, environmental safety, etc.). 

Acceptable risk is risk that is known, understood, and judged to be acceptable by an individual or a group. There are many different risk types that can be evaluated and accepted, such as cost risk, schedule risk, investment risk, programmatic risk, and safety risk. It should be noted that if risk is not identified or communicated, it is accepted by default without knowledge. An accepted risk does not necessarily mean that the risk has been made as low as potentially possible. 

The SHA is an analysis methodology for identifying hazards, evaluating risk and safety compliance at the system level, with a focus on interfaces and SCFs. The SHA ensures that identified hazards are understood at the system level, that aU causal factors are identified and mitigated, and that the overall system risk is known and accepted. SHA also provides a mechanism for identifying previously unforeseen interface hazards and evaluating causal factors in greater depth. 

The nuclear industry, for example, has a very low social tolerance of voluntary exposure to risk. The same is true in civil aviation, so here the trade-offs tend to be made in favour of safety initiatives, while targeting full and centralised coherence (and working to prevent isolated local actions). The same has not been true (at least until recently) in international finance, medicine, fishing and motoring, to cite just a few examples in these cases, senior management—or the institution in the broad sense—gives priority to exposure to risk and safety activities are mostly conducted at the local level, and it is accepted that they are local and limited in scope. 

W. W. Lawrence, Of Acceptable Risk, Science and the Determination of Safety, William Kaufman Inc., Los Altos, Calif., 1976. 

Vrijling, J. K., van Hengel, W. and Houben, R. J. 1998 Acceptable Risk as a Basis for Design. Reliability Engineering and System Safety, 59, 141-150. 

Fire and explosion are much more serious events than pollution. For one thing, fire and explosion can create catastrophes that will lead to poi ludon anyway, but for another thing, they can injure people. We clearl> want to have more levels of safety (that is, a lower probability of occurrence) in the chain leading to fire or explosion than is necessary in the chain leading to pollution. That is, whatever the acceptable risk lor <.)ii pollution, a lower risk is required for fire or explosion. 

---