Air conditioning and ventilation in buildings are major sources of energy consumption, particularly in large industrial buildings with significant pollutant and heat sources. Unfortunately, air flow motions in these slot-ventilated large building spaces are currently poorly understood, particularly concerning their special flow behaviours - multiple steady flows, i.e., identical boundary conditions but different initial conditions or load perturbations may lead to two or more flow solutions. Multiple steady enclosure flow behaviours essentially complicate the convective transport of air, heat and species, which has been vividly analyzed by streamlines, heatlines and masslines. In the present study, the flow mechanisms and transitions driven by combined natural and forced convections in an industrial building space for a welding process will be investigated through the numerical methodology of computational fluid dynamics. The research has taken into consideration the effects of ambient air temperature, indoor heating loads, and welding shifting position on multiple flow motions. The parameters governing the problem are the Reynolds number (10(3) <= Re <= 10(7)) and the Grashof number (10(7) <= Gr <= 10(13)) and it is observed that the multiple-steady-regions can be maintained for a range of values of Gr/Re-2, 150 < Gr/Re-2 < 1000, 6500 < Gr/Re-2 < 12,500 and Gr/Re-2 similar to +infinity with proper conditions. (C) 2018 Elsevier Ltd. All rights reserved.