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The law says these costs should be As Low As Reasonably Practicable (ALARP). This is intended to ensure that, while operations are safe, the costs do not render companies financially incapable of operating.
The ALARP principle was enshrined in UK law in 1949, and in the Health and Safety at Work Act 1974, which requires “provision and maintenance of plant and systems of work that are, as far as reasonably practicable, safe and without risks to health”.
This is interpreted to mean that risks must be reduced to an ALARP level. In short, duty holders must reduce risks unless the cost of doing so is grossly disproportionate to the benefits. The law assumes that safety measures are implemented unless they are ruled out due to being disproportionately costly.
Duty holders need to ensure that all reasonably foreseeable hazards have been identified, and that all “reasonably practicable” control measures are implemented unless they are “grossly disproportionate”.
This requires the costs and benefits of a control measure to be compared. The Health and Safety Executive (HSE) provides guidance “to spend £1m on preventing five staff suffering bruised knees is grossly disproportionate, but to spend £1m on preventing an explosion that would kill 150 people is obviously proportionate”.
ALARP applies to everything from daily costs of supervising employees through to the management of rare but extreme events. It puts the obligation on the duty holder to determine the appropriate level of risk mitigation. It can be difficult to interpret and implement this vital law, particularly as an assessment of the balance of cost and benefit relies on an understanding of the likelihood of a hazard which can be specifically challenging when assessing complex engineering systems.
The IMechE Safety and Reliability Group have produced guidance to help engineers understand and discharge their responsibilities, as well as deliver robust safety engineering. A key element of this is the concept of the ‘Well-Reasoned Argument’ which is the rational explanation of how ALARP has been achieved, and where risk quantification is used to support the argument that it is based on sound statistics and robust data.
There’s also a ‘proportionality matrix’ that provides a framework to help engineers understand the level and depth of analysis they should undertake based on the worst reasonably foreseeable consequence. For example, ensuring compliance with recognised practice and standards may be sufficient for situations with limited potential for severity, but not for complex systems with potential for multiple fatalities.
ALARP is not static as the nature of the hazard, the mitigation costs and available risk mitigation technology change over time. Regular structured reviews are therefore required to ensure that risks remain ALARP.
Duty holders must be able to satisfy themselves that they have taken all reasonable measures to reduce the risk profile and also demonstrate that further measures do not pass the disproportionate test. Assessments and decisions relating to gross disproportion are rarely obvious and can be very subjective in nature. Organisations need to understand these difficulties and develop robust processes, that are appropriate given their specific context, to ensure that the risks associated with their products and operations are ALARP.
The IMechE report ALARP for Engineers: A Technical Safety Guide has been updated for 2024. Read it online.
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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.