Practical Elements of Safety contains the invited papers presented at the Twelfth annual Safety-critical Systems Symposium, held at Birmingham, UK in February 2004. The papers included in this volume focus on the themes of the identification and analysis of risk - using the UK railway as an industry example; safety-integrity levels; industrial use of formal methods; as well as expanding on the development, assessment and changing face of current safety issues. All the papers are linked within the broad context of safety-critical systems actvities and offer a practical perspective. Papers contain industrial experience, as well as academic research, and are presented under the headings of: Mature and Practical Formality, Managing Risk in the Railway Industry, Safety Integrity Levels, the Human Side of Risk, Assessment and the Derivation of Evidence, and Safety Argument and the Law.