Resilience of Operational Technology (OT) that is at the heart of our critical national infrastructure (CNI) is paramount as it comes under attack from a range of adversaries especially nation states. Because CNI is operated by and impact humans, it must maintain safe and continuous operations under sustained disruptive efforts by Advanced Persistent Threats (APTs). We will discuss approaches to security informed safety to improve resilience of OT systems. We will show how practitioners can use CyBOK, the Cyber Security Body of Knowledge, to develop their individual and organisational capabilities in this regard. A live demonstration will show how this knowledge can be deployed in practical settings to defend against sophisticated attacks such as Triton that impacted safety of critical infrastructures.