System safety tenets
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PtD concepts
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1.
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Systematically identify, evaluate, and control hazards in order to prevent (or mitigate) accidents
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Hazard analysis and risk assessment
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Risk treatment
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2.
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Apply a precedence of controls to hazards starting with their elimination, designing to preclude hazards, and finally administrative controls. Administrative controls include signs, warnings, procedures, and training. (The lowest precedence are those controls that rely on people.)
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Risk treatment
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The hierarchy of controls
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Layers of protection
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3.
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Perform proactively rather than reacting to events. This starts with a program plan.
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Risk management process
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Prevention through design
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4.
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Design and build safety into a system rather than modifying the system later in the acquisition process when any changes are increasingly more expensive
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Prevention through design
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5.
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Develop and provide safety‐related design guidance and give it to the designers as the program is initiated
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Prevention through design
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Design safety specifications
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6.
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Use appropriate evaluation/analysis techniques from the tabulated variety available
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Hazard analysis and risk assessment
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7.
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Rely on factual information, engineering, and science to form the basis of conclusions and recommendations
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Establish context
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Risk‐based decision making
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8.
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Quantify risk by multiplying the ranking of undesired consequences of an event by the probability of occurrence. There are variations to this “equation”
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Risk analysis
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9.
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Design, when allowed, to minimize or eliminate single‐point failures that have an undesired consequence. Make at least two‐fault tolerant, that is tolerant of multiple faults or system breakdown that would have adverse safety consequence
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Prevention through design
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Layers of protection/defenses
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10.
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Identify, evaluate, and control hazards throughout the system's life and during the various operational phases for normal and abnormal environments
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Prevention through design and re‐design
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Design safety reviews
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Management of change
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System's lifecycle
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11.
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After application of controls to mitigate a hazard(s), management must recognize and accept the residual risk
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Acceptable risk level
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As low as reasonably practicable (ALARP)
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12.
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Recognize the quality assurance interface: (i) Decrease risk by using materials that are properly specified and possess adequate quality assurance and (ii) implement to continually improve the system
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Design safety specifications
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13.
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Tabulate and disseminate lessons learned and incorporate those lessons for future safety enhancement
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Risk communication and consultation
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14.
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Apply system safety to systems to include processes, products, facilities, and services
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Prevention through design
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15.
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Recognize that near‐miss conditions, if not corrected, most likely develop into accidents
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Hazard/risk identification
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Risk assessment
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Risk treatment
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Source: From Lyon et al. (1). © 2019.
A review of Table 2 reveals that there are strong correlations between system safety and PtD concepts. The concepts of risk avoidance and reduction through assessment, treatment, and design into system elements are fundamental to both system safety and PtD.
5 Z590.3 PREVENTION THROUGH DESIGN
The ANSI/ASSP Z590.3‐2011(R2016) (11) standard defines PtD as “addressing OSH needs in the design and redesign process to prevent or minimize the work‐related hazards and risks associated with the construction, manufacture, use, maintenance, retrofitting, and disposal of facilities, processes, materials, and equipment” (ANSI/ASSE Z590.3‐2011(R2016)). ANSI Z590.3's stated goals are to (i) achieve acceptable risk levels, (ii) prevent or reduce risks that produce injuries and illnesses, and (iii) reduce the need for retrofitting to control risks not addressed in the design phase. Its concepts can be applied in any setting and throughout the life cycle of a system's life. The four major stages identified in Z590.3 are as follows:
1 Pre‐operational. The initial stage including conceptual design, initial planning, design, specification, prototyping, construction, and installation which offer the designers the greatest degree of control and lowest costs.
2 Operational. The primary stage of the life cycle including production, maintenance, service or repair, redesign, modification, and addition of a system. Hazards and risks are identified, assessed, and treated with work method changes or retrofitting of physical elements to the system through redesign initiatives.
3 Post‐incident. A reactionary stage following incidents such as injuries, illnesses, fatalities, property damage, equipment failure, product failure, near‐hits, or noninjury incidents, and other unwanted events. Investigations and analyses of causal factors are used to determine appropriate interventions to reduce recurrence or control similar exposures to an acceptable risk level.
4 Post‐operational. The final stage or end of life,
