Dates: Dec 1, 2024
In most cases, risks cannot be eliminated, only reduced to a level that everyone who has a stake in the activity or process finds tolerable when weighed against the advantages and benefits of the activity or process (see Figure 1). Usually, risks will be tolerated in exchange for an economic or societal benefit.
Figure 1: As low as reasonably practicable (ALARP) risk concept
Because attitudes about the tolerability of risks are not consistent, there are no universal norms for risk tolerability. What your stakeholders view as a tolerable risk will depend upon a number of factors, including the following:
The nature of the risk ― Is it a voluntary risk, one that those who are at risk accept as part of a choice? Or is it involuntary?
Who or what is at risk ― Does it affect a single person or many people? What about the surrounding environment? Is it an industrial landscape already altered by past uses, or a pristine or prized natural setting? Are important water or other resources at risk? Residential neighborhoods? Schools?
The degree to which the risk can be controlled or reduced ― Process safety design and especially emergency relief system design focus in large part on this issue. Making the case for a “tolerable” risk requires that the methods supporting the design basis be technically sound and defensible, clearly documented, and accurate.
Past experience ― Uncertainty regarding the risk impact influences the risk takers' tolerability. For example, the average person understands the risk of driving an automobile but is uncertain regarding the risk of nuclear power generation.
Finally, attitudes toward risk change over time. Given all of these variables, how does a company establish risk criteria that can effectively contribute to decisions about the tolerability of certain consequences, likelihoods, and risks?
Companies that have successfully established risk criteria focus on providing consistency in their decisions about risk. These criteria typically represent levels of risk that the company believes will minimize impacts to continued operations. This approach does not explicitly mention specific stakeholder concerns such as protection of the surrounding environment and communities. However, risk decisions that protect operations are very likely to help reduce risk across the board for facilities, employees, surrounding property, and the environment. Moreover, since demonstrably safe operations have become a cornerstone of a company's franchise to operate in many places, well-thought-out risk criteria that make continued operation their objective will also address most other stakeholder concerns.
Risk criteria should also fit with a company's philosophy and culture and match the type of analysis its engineers normally conduct in the design stage. The selection of appropriate risk criteria is a corporate responsibility and requires the involvement and support of senior management, as it establishes the levels and types of risks the company will tolerate.
Once a company has established specific risk criteria, they can be used to check outcomes throughout the design process, at Steps 3, 5, and 8 of the approach as outlined in the Risk Considerations for Safe Process Design white paper. This iterative approach builds consistency into the process and increases the likelihood of making risk-based choices early in design – where they are often most cost-effective.
A facility belonging to a large chemical manufacturer was producing a family of chemicals that react vigorously with water, generating corrosive and toxic by-products. The production process utilized water-cooled heat exchangers for condensing and cooling the process streams. Given the hazard potential due to exchanger leaks, the facility had embarked on a program to reduce the risk of such an event. However, they needed a way to determine which risk reduction option or combination of measures was the most effective.
Working closely with the company's operations and design engineers, we utilized elements of a risk-based approach to determine the relative benefit of various risk mitigation alternatives. The approach involved a qualitative estimate of the consequences of exchanger leaks, since almost any size leak would result in an undesirable outcome. A quantitative determination of the likelihood of such events for different risk reduction measures was also conducted to establish the relative benefit of the various options. The results were presented to a group of engineers and managers, to allow them to decide which option would meet their risk tolerability criteria. The company opted for the inherently safer solution of substituting a non-reactive coolant for water. While the selected design approach was not the lowest capital cost alternative, there were offsetting operating cost benefits in terms of less maintenance cost, downtime, and administrative complexity.
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The ioMosaic team has extensive experience conducting facility siting studies, assessing plant facilities, and providing recommendations to manage risk. We are particularly proud that so many of our clients return to us for facility siting studies and guidance regarding expansions, modifications, and new facilities; and that they continue to rely on us for integrity, insight, and value. Our recommendations are practical and based on sound engineering practices, while keeping operability and cost-effectiveness in mind.
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