Machine safety law rests on a foundational principle: the protection of the operator. Across legal systems, safety regulations require that machines be designed and operated so that dangerous situations can be stopped before injury occurs. This protection is not a new legal objective but an obligation already embedded in existing law — the stop-function and emergency-stop requirements of Directive 2006/42/EC (and the forthcoming Regulation (EU) 2023/1230, which expressly addresses machines with autonomous behaviour), the product-safety duties of Switzerland's LSPro (RS 930.11), and the operator-protection requirements of OSHA (29 CFR § 1910.212).
This paper argues that such protection rests on an implicit temporal assumption: that the operator retains a meaningful opportunity to perceive a developing hazard, evaluate it, and intervene before harm occurs. Traditional machinery generally satisfies this assumption; it can fail whenever a machine produces operationally significant effects faster than human reaction allows. In such circumstances the operator's legal protection formally remains in place, while the practical conditions for exercising it disappear. The resulting problem is not regulatory absence but legal effectiveness: existing obligations remain valid yet can no longer be realised through human intervention alone.
To address this gap, the paper introduces the concept of systemic arrestability: a system is systemically arrestable when its capacity to halt a hazardous action does not depend on a human operator perceiving, evaluating, and intervening within the time window of that action. The concept creates no new legal obligation; it preserves the practical effectiveness of obligations that already exist. Through a comparative analysis of the European, Swiss, and United States machine-safety frameworks, the paper proposes systemic arrestability as an interpretative standard for maintaining the protective purpose of existing safety law under conditions in which machine speed exceeds human reaction capacity.
operator safety · machine safety · stop function · emergency stop · human reaction time · legal effectiveness · systemic arrestability · Directive 2006/42/EC · Regulation (EU) 2023/1230 · LSPro RS 930.11 · OSHA 29 CFR § 1910.212
The temporal structure analysed in this paper is not unique to civil machine-safety law. For the parallel argument in the context of International Humanitarian Law and autonomous weapons systems, see: Lawful Operational Safeguards in AI Systems (2026). The convergence of the two analyses indicates that the effectiveness problem identified here is structural rather than regime-specific.