• A systematic review reveals no universally accepted definition of safety ‘control.’ • Terms like control, barrier, defense, and safeguard are used inconsistently. • Existing classification frameworks lack empirical validation and clarity. • Ambiguity limits effective implementation of controls in high-risk environments. • Establishing clear, agreed definitions is essential to advance both scientific rigor and practical application in safety management. Introduction: The concept of control has been central to safety management, evolving from early machine‑guarding statutes to a key role in accident prevention and risk science. Interestingly, it now underpins the modern view that safety is the presence of controls rather than the absence of injury. More importantly, poorly defined or insufficient controls remain a routine root cause of accidents, yet the term still lacks a shared, accepted definition. Method: To this end, we conducted a PRISMA‑guided systematic review of peer‑reviewed and gray literature, asking: (1) what definitions of control exist? (2) what categories or types are proposed? and (3) how is control effectiveness evaluated? The review was limited to documents discussing controls as preventive or defensive measures, under specific inclusion and exclusion criteria. Results: In the corpus examined, the study identified no single, agreed-upon definition of control. Terms such as barriers, defenses, and safeguards are frequently conflated, and, notably, even the widely referenced term barrier is used inconsistently in the literature and standards. Additionally, although multiple classification schemes exist, none provides a validated framework for categorization or adequacy assessment, leaving systems vulnerable under abnormal conditions. The Hierarchy of Controls, dominant in safety standards, rests more on professional consensus than on empirical evidence and therefore warrants further scrutiny. Energy‑based safety thinking, particularly the notions of direct control and high‑energy thresholds, offers a promising path for defining and evaluating controls. Practical Applications: The practical application of this work lies in its potential to support a more precise and consistent understanding of what constitutes a safety control. Addressing current ambiguity enables practitioners to better design, implement, and assess effective controls in high-risk environments, thereby strengthening interventions and advancing more informed decision-making across research and practice.
Raheemy et al. (2026) studied this question.