Making an ALARP Decision of Sufficient Testing

ALARP is an important concept in many safety standards. It helps in making a decision about how tolerable a risk is. A tolerable risk should be reduced to a point that is As Low As Reasonably Practicable (ALARP) which implies further risk-reduction is grossly inappropriate compared to the benefit attained. To date work has considered the process, safety arguments, and influencing factors of how to make an ALARP decision but not shown how to make a quantified judgement for it. In this paper a method for making an ALARP judgement decision is proposed in the context of testing the worst-case timing properties of systems. The method is based around a convergence algorithm that informs the tester when it is believed that testing for longer will not reveal sufficiently important new findings, i.e. any significant increase in observed worst-case timing needs a disproportionate amount of testing time.