Beyond static hazard labels: a two-layer temporal object-attribute model of construction accident escalation

Construction safety research often categorises hazards as fixed labels, such as falls, electrocution, or struck-by. This supports reporting but explains little about what makes a condition hazardous and how the condition evolves over time. Accident prevention requires an understanding of how a hazard becomes critical and when worker exposure becomes harmful. This paper develops and demonstrates a two-layer temporal object-attribute model that explains accident escalation as the coupling of worker-independent hazard growth and worker-specific exposure evolution. A hazard is redefined as a worker-independent temporal state of objects, hazardous attributes, relations, controls, and an impact zone. Worker exposure is modelled separately, as the worker’s relation to that state and its impact zone. An accident occurs when a critical hazard state and a harmful exposure state align under actuation conditions. The model is applied through backward reconstruction of 1065 OSHA construction accident reports across six categories: fall, heavy equipment, confined space, electrocution, struck-by falling object, and fire-related explosion. The analysis reconstructs precursor hazard states, exposure configurations, transition mechanisms, and terminal hazard, exposure, and accident states. Escalation was driven mainly by relation change rather than new energy, and the pathway differed by category. Falls and confined spaces escalated through exposure around an already hazardous condition, whereas electrocution, struck-by, and heavy-equipment cases required an explicit change in the hazard state. The paper contributes a temporal object-attribute definition of construction hazards, a two-layer account of escalation through hazard-exposure coupling, and an empirical demonstration of accidents as coupled trajectories.