Towards a maximum wind speed for ventilated asbestos removal worksites

To prevent public and occupational exposure to hazardous airborne fibres during asbestos abatement, regulations impose to maintain worksites at a negative pressure compared to outside, and to dilute indoor fibre concentration by means of a minimum air change rate. However, recent studies have revealed significant effects of wind on the containment of asbestos worksites. The wind can induce negative external pressures with a magnitude higher than the internal pressure produced by mechanical ventilation, thus breaching the containment. This research study proposes to determine a wind speed threshold above which it becomes practically impossible to ensure the worksite containment. The approach followed is based on transient simulations of ventilation networks, using the SYLVIA tool, supplemented by wind pressures from the Tokyo Polytechnic University database. A total of 360 combinations of wind conditions and worksite configurations were evaluated. The results highlight two wind speed thresholds (defined at 10 m height) for design pressures from -10 to -40 Pa: (1) below 6.5 m/s, no significant containment breach is identified, and (2) above 12.5 m/s, the robustness of all containments is questioned regardless the wind direction. These findings can be used by preventers and specialized companies during asbestos abatement or other worksites under containment.