Lean but strained: a socio-technical explanation of the safety paradox in just-in-time modular construction

Purpose Although just-in-time (JIT) systems drive efficiency, their underlying trade-offs regarding employee safety in modular construction remain critically under-researched. Addressing this gap in socio-technical operations literature, this study investigates the impact of JIT practices on employee safety and evaluates how operational strain and supplier integration alter this relationship in low-slack production environments. Design/methodology/approach A two-wave, multi-informant survey design was employed to separate predictor and outcome variables across respondents and time, thereby reducing common-method bias. Data were collected from 346 matched responses from managerial and frontline personnel across 103 modular construction firms operating in a developing economy context characterised by high supply variability and infrastructural constraint. The hypothesised moderated mediation model was estimated using Partial Least Squares Structural Equation Modelling (PLS-SEM), with robustness verified through a Gaussian Copula endogeneity correction, full collinearity assessment, and PLSpredict cross-validated predictive relevance. Findings Results show that JIT is positively associated with employee safety but simultaneously increases operational strain. Contrary to a priori expectation, operational strain is positively associated with safety, suggesting short-term compensatory vigilance, and consistent with HRO theory. Mediation analysis reveals that operational strain partially explains the JIT–safety relationship. Furthermore, high supply reliability attenuates the strain-inducing effects of JIT, serving as a stabilising boundary condition. Practical implications Managers should align JIT implementation with supply reliability and closely monitor operational strain to sustain efficiency without compromising worker safety. Originality/value The study conceptualises JIT as a variability-redistribution mechanism that reallocates operational pressures to frontline employees, offering a behavioural explanation for the lean–safety relationship in Prefabricated-JIT systems.