This article analyses the role played by standards of protection in the regulation of catastrophic risks. It examines how to protect people against the occurrence of catastrophic events, considering that the related risk is highly uncertain and difficult to predict using rational methodologies. In this perspective, the article focuses on environmental risks and terrorist threats affecting common goods – namely environment and security – areas where any damage is susceptible to producing ruinous effects and huge casualties. Both natural and man-made disasters are capable of altering the normal legal relations that States are institutionally to ensure to their citizens. Therefore, the severity of the consequences of catastrophic events cannot be ignored, despite the low probability of their occurrence. However, in the absence of emergencies, exceptional measures may be adopted as a means of altering the legal framework, and thus the enjoyment, of fundamental freedoms and priorities in the allocation of public resources. No precautionary approach can escape from rational reflections about the opportunity-cost of any action, the cost-benefit analysis of countermeasures and the proportionality of every regulatory decision. In order to understand how to face those “low probability – high cost” risks, the article considers a specific method of regulating risks by resorting to standards of protection. By using thresholds of alarm, public administrations can decide upon best-fit countermeasures that will correspond to specific risk characterisations. To this end, the article analyses the administrative process of formulating standards and how they enable uncertain risks to be managed, thus promoting the development of a sound and accountable administration.